Physiology, genomics, and evolutionary aspects of desert plants

Graphical abstract

Highlights

• •Desert is one of the harshest places on the earth due to low precipitation and soil nutrients.
• •Global desertification is a continuous process; almost 60% of the land surface is now desertified.
• •The plants in these desert ecosystems have developed several novel phenotypic characteristics that overcome the harsh environment.
• •Genome sequencing of the desert plant can enable us to identify the novel trait responsible for overcoming the xerophytic condition.
• •Transfer of novel genetic traits can be done to the crop plants. So that plants can withstand the harsh environment and overcome crop loss due to drought and other extreme conditions.

Abstract

Background

Despite the exposure to arid environmental conditions across the globe ultimately hampering the sustainability of the living organism, few plant species are equipped with several unique genotypic, biochemical, and physiological features to counter such harsh conditions. Physiologically, they have evolved with reduced leaf size, spines, waxy cuticles, thick leaves, succulent hydrenchyma, sclerophyll, chloroembryo, and photosynthesis in nonfoliar and other parts. At the biochemical level, they are evolved to perform efficient photosynthesis through Crassulacean acid metabolism (CAM) and C4 pathways with the formation of oxaloacetic acid (Hatch-Slack pathway) instead of the C3 pathway. Additionally, comparative genomics with existing data provides ample evidence of the xerophytic plants' positive selection to adapt to the arid environment. However, adding more high-throughput sequencing of xerophyte plant species is further required for a comparative genomic study toward trait discovery related to survival. Learning from the mechanism to survive in harsh conditions could pave the way to engineer crops for future sustainable agriculture.

Aim of the review

The distinct physiology of desert plants allows them to survive in harsh environments. However, the genomic composition also contributes significantly to this and requires great attention. This review emphasizes the physiological and genomic adaptation of desert plants. Other important parameters, such as desert biodiversity and photosynthetic strategy, are also discussed with recent progress in the field. Overall, this review discusses the different features of desert plants, which prepares them for harsh conditions intending to translate knowledge to engineer plant species for sustainable agriculture.

Key Scientific Concepts of Review

This review comprehensively presents the physiology, molecular mechanism, and genomics of desert plants aimed towards engineering a sustainable crop.

Introduction

The earth is facing a global environmental crisis and a continuous increase in aridity in the sub-tropical region contributing to continuous increase in the desertification [1], [2]. Although no specific definition of desert exists, it is widely agreed that desert is characterized by the arid terrestrial ecosystem that receives little precipitation (<250 mm/year) and higher evaporation [3], [4]. This leads to poor soil–water balance leading to the creation of low coverage of vegetation [5]. In the ancient literature, the desert is called “a place where faith is tested, and spirit is renewed”. Although water is one of the most important limiting factors in the arid desert ecosystem, but the duration of absence, intensity, and timing also play important roles towards the vegetation [6]. Since 2016, global desertification has surged from 48 to 65% of the total land surfaces [1]. Desert is one of the harshest environment on the earth due to extreme drought [7], temperature [8], [9], salinity [10], low nitrogen availability [11], [12], and extreme UV radiation [13]. It is also one of the earth's driest environments, enabling researchers to investigate how organisms have adapted to such challenging environmental conditions. However, the main challenges in the arid desert ecosystem are to maintain body temperature and preserving water [14], [15]. The organismal behavior necessary to adapt and survive such extremely harsh conditions from generation to generation usually falls outside the range of the normal plant plasticity [16], [17]. Such adaptation strategy unveiled that desert-inhabitant species experienced a strong selection pressure for photosynthesis, transpiration, pH, and water retention [18], [19].

Further, their anatomy of leaf, root, stem, flowers, pollens, and fruits, also undergoes extensive modification to avoid excessive desiccation and water loss [20]. Most importantly, even if the desert ecosystem is very harsh, hundreds of thousands of plant species still inhabit the desert ecosystem across the globe. A common adaptive feature found in the maximum of desert plants (xerophytes) is storing water, minimizing water loss rate, maximizing photosynthetic rate, and regulating the energy budget [21]. In addition, the desert plant develops a strong and deep root system to adapt itself. Despite the understanding of physiology of plants in desert environment, genomic composition unveils the differences from plants species growing in favorable environment [22], [23]. High quality genome sequencing can identify the genomic region with alleic diversity across different species and comparison with other land plants could help in understanding the molecular mechanism behind the strategy to survive in harsh environment. Enormous effort has been undertaken to use the arid land for sustainable agriculture. However, their harsh environmental condition always becomes challenging for the agricultural production. Still, researchers are trying hard to develop new crop varieties that is able to withstand the arid environment for a sustainable agriculture. So, the vast majority of the arid land can be utilized efficiently to eradicate world hunger. However, a lack of sufficient research on the physiology, genomics, and molecular aspects of the desert plant makes it difficult to bring profitable biotechnological implications of desert traits to crop plants. Therefore, in this review we tried to present an existing knowledge and perspective of the desert plant’s physiology, genomics, and evolution.

Desert biodiversity and adaptation strategies

Approximately 33% of the terrestrial land is classified as desert due to its common features of arid weather, low soil-nutrient, harsh temperatures, and others. The weather of the desert is extremely variable, leading to variable biotic composition in the ecosystem [22], [23]. The desert formation can be attributed to local, regional, and global conditions. The rate and type of desert formation are directly associated with its biodiversity [24]. The activities of the desert plant are highly regulated by the availability of water and period of severe water limitation [25]. These pulses of the water cycle greatly balance the ecology and evolution of the desert biota [26], [27], [28]. The desert vegetation grows extremely slowly and, once disturbed, can take hundreds of years to restore. Sometimes, the biota of the desert environment is so fragile that the entire population gets wiped out from the habitats [29], [30]. In a desert environment, it is common to notice the separation of plant biota from each other [31], [32]. This gives them enough space to avoid competition and resource allocations [33], [34], thus allowing accessibility to the soil nutrients without competition.

Further, if there is any pathogen attack or other adverse effect, the space between them prevents the spread of diseases from one species to another [35]. This gives them an advantage in adapting the desert environment (Fig. 1). However, wateris one of the most critical limiting factors in the desert environment, so the pattern of rain and drought cycle most possibly lead to the development of drought-avoiding and drought-tolerant species [36], [37], [38]. The drought avoider has the edge over others due to a mechanism to circumvent the situation, or sometimes they become inactive by dying or hibernating [39], [40]. The annual plants are the most common type of drought-avoiding plants because they become active only during favorable environmental conditions and die when conditions become harsh [41]. The annual plants usually do not grow during drought [42], [43]. The drought-evading plants preferentially grows during the drought period [44], [45], but they sometimes become inactive during the early stages of water stress. The dry deciduous plants are usually drought-evading, and they avoid such situations by shedding their leaves [46]. The drought-evading plants usually show higher growth potential due to adaptive trait that reduces water loss. The most common features of drought evader plants are the presence of extensive root system [47], stomatal pits, smaller leaf size [48], leaf hairs [49], and waxes [50]. However, the drought-resisting plants show low-to-moderate growth activities. Reduced transpiration is one of the most critical features of drought-resisting plants. The succulent plants and perennial shrubs fall in the category of drought resister. The dynamics of the desert ecosystem and their global distribution enable us to understand plant adaptation strategies at different timescales. They can provide us unique opportunity to understand the convergent evolution of distinct times and spaces [51]. However, the desert adaptation has also lacked accurate environment-genotype-phenotype maps [51].

Fig. 1.

Figure depicting the succulent plants of the desert ecosystem. Figure (A-B) cactus and (C-D) Zygophyllum have the potential to store water in their body. The photograph of the cactus plant was taken from a high mountain where it tried to mimic itself as the color of the soil and stones. The flowering body also looks quite strong and highly pigmented. (C-D) Zygophyllum sp. Hold water in their thick and long leaves (Close view of figure C).

Leaf architecture and stress avoidance strategy

The plant develops various types of leaves for its different physical and physiological strategies. The form of variation seen in nature is quite fascinating. How these variations developed in ontogeny for desert adaptation and through evolutionary time periods is quite important to understand. The most prudent adaptive strategy for the leaf is associated with maintaining the leaf temperature and heat dissipation by latent heat transfer [52]. The latent heat transfer is mainly associated with the rate of transpiration. During the summer, when moisture and water content are limited, latent heat transfer becomes very challenging, leading to functional diversification and adaptation of desert leaves [53]. To avoid a high transpiration rate, desert plants develop reduced leaf size [21]. Reduced leaf size is desert plants' most adaptive morphological feature [54]. The reduced leaf size and surface area restrict the transpiration rate, leading to low water loss. The smaller leaf with the reduced surface area has the potential to absorb lesser heat from the sunlight, thus making it cooler. Lower temperature also reduces photorespiration and brings it closer to the thermal optimum for favorable photosynthesis [55]. Also, the leaves of desert plants have reduced boundary layers that enable higher heat transfer from the leaf to the surroundings; thus, higher convective (less dependent on latent heat transfer) heat loss maintains the leaf temperature closer to air temperature [56], [57].

The leaf of the desert plant also develops reflective waxes and leaf hairs on the surfaces that reduce direct solar radiation [50]. The leaves also develop a thick layer of trichomes [58] that strongly reflect the solar radiations, thus making the leaf cool [59]. The leaf angle to the sun is also a major factor of desert plants. Some desert plants (annual) develops diaheliotropic (perpendicular to the sun rays) leaf [60], [61], whereas some other develop paraheliotropic (parallel to the sunrays) leaves [62], [63]. Diaheliotropic leaves allow absorption of maximum solar radiation and can be beneficial for plants that grow for a short duration [64], [65]. That's why most of the annual desert plants develop diaheliotropic leaves [66], [67]. Some plants show diaheliotropism and paraheliotropism at different times of the day. Lupinus arizonicus is a classic example in this category [68]. It shows diaheliotropism in the early morning and paraheliotropism later in the day [62]. The switch from diaheliotropism to paraheliotropism drastically reduces leaves' heat load and transpiration. Although most leaf of the desert plant is not heliotropic (sun orienting), the leaf angle can have an enormous impact on interception, absorbance, and energy balance. The desert plants preferred vertically biased and non-random (fixed) leaf angles. The majority of the desert species having non-random leaf angles undergo a switch between dia- and paraheliotropism [53], [69]. So that they can capture the soft sunlight of morning and late afternoon and avoid the severe solar radiation during the mid-day. The non-random leaf angle also reduces the possibility of self-shading enabling higher photosynthetic efficiency of other leaves and stems [70], [71]. The stem of the succulent plant Copiapoa cinerea orients towards the north, reducing solar radiation during the dry season and facilitating apical warming during the cold period.

The leaf of the desert plant develops a thick wax layer and leaf hair to avoid high-temperature irradiance. The leaf hairs can be in the form of trichomes that can firmly provide support to the leaf by reflecting solar radiation [72], [73]. However, sometimes the thickness of the trichomes and its reflectance depends upon the level of water stress experienced by the plants [74], [75], [76]. The trichomes have the potential to absorb approximately 80% of the solar radiation, thus protecting the leaf from excessive heat exposure. The attenuation of heat load by trichomes reduces the rate of transpiration, thus protecting the plant from excessive water loss [77], [78].

Roots system in desert plants

Maintaining a necessary water balance for the survival of the plant is one of the key strategies in water-deficit environment but often is challenging. Therefore, the desert plants evolved with traits that can accelerate maximum water uptake during its availability. Simultaneously, it should also prevent water loss. Roots are the most promising organ of the plant that facilitates water uptake. Since deserts are always in water- scarcity, it can be easily believed that plants residing in the desert environment must develop their root architecture far better than other plants. However, it is also highly possible that an arid climate can quickly dry up the roots and be fatal to the plants. Therefore, the maintenance of an extensive root area will be very costly for the plants in the desert. To avoid such problems, desert plants prefer to produce a long root system that can access a permanent water supply from the water-saturated soil zone (phreatophytes). A plant named Boscia albitrunca of Kalahari desert is reported to have 68 m of the deep root. Desert plants are also reported to develop rhizosheath around their roots [79], [80], [81]. In rhizosheath, agglutination of soil occurs around the soil. It was reported that rhizosheath positively impacts soil nutrition and aridity [82], [83], [84], [85].

Most desert plants develop their root system according to their requirement of soil water distribution. The passage of water in xerophytic plants occurs via a symplastic pathway that leads to a decrease in ²H of root xylem water relative to the surrounding soil medium [86]. Most desert plant species grow upon the embryonic root/primary root, and a few species develop seminal embryonic roots. Some species also develop shoot-borne nodal roots [87], [88]. Desert plants also decide, on where they should depend for their water uptake, whether it's from the soil surface, deep-soil water, or both [89], [90], [91], [92]. Most of the bushes from Chihuahuan desert show a distribution of horizontal root systems upto a few meters deep into the soil [89]. Some desert grasses of the Chihuahuan desert show later spread of roots to 50–100 cm in the upper 1.5 m of the soil [89]. These roots most possibly capture the maximum amount of available water during the rainfall. For water, the annual and perennial succulent plants entirely depend upon the summer precipitation, whereas herbaceous and woody perennial species use summer and winter-spring precipitation for their water [89]. The lateral roots react to the soil's water gradient and the main roots serve as an anchorage in the soil to facilitate groundwater in the deep soil [89]. The roots of Opuntia plants are distributed horizontally up to 2.5 m from the origin of the plants, and it is distributed 1.5 m uppermost of the soil [89]. This indicates Opuntia plants feed on water from the upper soil layer. Further, the cactus plant Opuntia develops adventitious roots to strengthen the anchorage and improve water uptake. The development of the lateral roots occurs quickly, and its growth is arrested. The development of second-order lateral roots occurs from the first-order lateral roots [89]. The development of lateral roots is also triggered when root apical meristem is damaged indicating apical meristem is the key player in the development of the lateral roots. Identifying the responsible genetic trait that plays such a critical role in lateral root formation is important.

Root transcriptome analysis revealed the roles of genes associated with auxin and cytokinin signaling in Pachycereus pringlei [93]. The genes related to root development included AUXIN RESPONSE FACTOR and SMALL AUXIN UP RNA [93]. Transcriptome analysis of cactus Pachycereus pringlei identified the orthologous Arabidopsis genes for developmental regulator [93]. The orthologs were SHR (short root), SCR (scarecrow), JKD (jackdaw), and GRAS-domain (GAI-RGA-and-SCR) transcription factors [93]. These orthologs regulate ground tissue and quiescent center (QC) specification in Arabidopsis [93], [94]. The up-regulation of abscisic acid (ABA) regulated genes was also reported to be found at the determinate stage [93]. Further, succulent plants like Opuntia and Agave has the potential to develop rain root in response to rainfall [95], [96], [97].

Development of chloroembryo & photosynthesis in Non-Foliar tissue

Xerophytic plants usually develop small, thick leaves [98], [99], [100]. Sometimes, to avoid excessive transpiration and water loss before the completion of their life cycle, some of the xerophytic plants develop chloroembryo [101]. In the chloroembryo, the embryo of the plant contains chlorophyll, and it remains in the chlorophyllus stage until the completion of the life cycle [101]. Due to chlorophyll's presence, these embryos can conduct photosynthesis. However, the chloroembryo is found deep inside embedded with the supporting tissues with shade adaptive strategy [101]. The chloroembryo is reported to encode characteristics for low light saturation point and low chlorophyll a/b ratio for photosynthesis [101]. Further, it is reported to have low Calvin cycle enzymes in the chloroembryo compared to the leaves [101]. It also contains a large PS II antenna directly related to the low chlorophyll a/b ratio [102]. At least 428 species (224 genera) are reported to possess chloroembryo [101], [103]. From them, some of the species grow in an arid environment. However, the pigmentation and patterning of chloroembryo of different species vary greatly and are sometimes restricted to a particular area of the organ. Citrus sp. is a classic example that contains chloroembryo [101]. The chloroembryo helps to accumulate net carbohydrate content. Although the tomato plant is not native to desert environments, it has still developed photosynthetic apparatus in its fruit. The photosynthesis in tomato fruit contributes around 10–15% of net sugar accumulation [103]. Plant pericarp is also a non-foliar green tissue with chlorophyll content capable of conducting photosynthesis. The desert cactus plant is capable of performing photosynthesis in its stem. One desert plant named Euphorbia masariensis has rudimentary leaves. It contains green stems with chlorophyll content that enable the plant to conduct photosynthesis. A study conducted by Kocurek et al., (2020) found that stems covered with dark materials significantly reduce the root biomass compared to the control, suggesting stem photosynthesis's role in plants [104].

Stem of desert plants

Further, due to the presence of small and rudimental leaves, the xerophytic plants also preferred to conduct photosynthesis in stem and other non-foliar parts. The internal CO₂ content in plant Erigonum inflatum is reported to be very high [103]. However, the CO₂ fixation rate of a such organ is very low. The presence of smaller stomata in the stem leads to lower water loss and thus a high carbon gain. A study of 11 desert species reported strong coordination between leaf and stem photosynthesis and hydraulics [105]. The stem photosynthesis rate is comparatively higher in the dry season in an increased light interception that facilitates additional carbon gain and drought tolerance [103]. The presence of stem, leaf, and chloroembryo photosynthesis in plants contributes enormously toward the overall carbon gain and helps the plant to survive dry and hot environmental conditions [101], [103]. All the photosynthetic proteins, including light-harvesting protein psaA (PSI), psbA (PSII), chlorophyll a and b binding protein, plastocyanin, cytochrome b/f, ferredoxins, iron-sulfur protein, Rubisco, and fructose 1,6-bisphosphate reported presenting in the chloroembryo and non-foliar parts of the plant to conduct photosynthesis [106], [107]. This non-foliar organ contributes to the photosynthetic carbon assimilation and net assimilator of CO₂. Reduction in the photosynthetic gene expression using antisense technology led to a delay in tomato seed development [108].

Development of succulent structure

C4 and CAM desert plants have developed different adaptation strategies to avoid water problems [109]. They developed succulent structures in their body enabling them to store water (Fig. 1) [110], [111], [112]. Succulents are defined as a mechanical approach having the presence of water storing living tissue in one or more organs [113]. The succulent plants possess characteristics such as (i) the potential to store water in living tissue, (ii) the stored water can be utilizable upon requirement [113], and (iii) maintaining metabolic activity independent of water supply (Fig. 1) [114]. Although the majority of succulents possess CAM metabolism, all CAM plants are not succulent. Some succulent plants with CAM can switch to C3 photosynthesis when they get favorable environmental conditions. The succulent plants contain large water storage cells. The succulent structure depends upon several characteristics, including tissue cell volume, cell packaging, and tissue structure [113]. The water content of the succulent plants can reach 90–95% [113]. This hydraulic potential of the desert plants is a fundamental principle to maintaining ecophysiological strategy. The water-storage tissue hydrenchyma is the major player in the storage of water for succulent plants [115], [116]. The desert succulent plants that store water are usually perennial species [117], [118]. They use the stored water to buffer the transpiration, water potential during drought, and refilling of hydrenchyma during water availability [119], [120]. The presence of low surface area characterizes the succulent plants to the volume ratio that enables them to store the maximum volume of water [113]. The high cell volume in the succulent plant is also beneficial for conducting CAM as CAM requires large vacuoles to store organic acids produced during CO₂ fixation. As the gas exchange of CAM plants occurs at night under the ambient humidity, it confers enhanced water-use efficiency.

Photosynthetic strategy of desert plants

Desert plants are always under strict environmental conditions due to excessive water loss in the arid environment. In the majority of the cases, it leads to plant death. To conduct efficient photosynthesis, it needs the uptake of environmental CO₂. But, due to the presence of fewer stomata, it becomes a limiting factor for photosynthesis [121], [122]. Although there are several limiting factors for plant growth in the desert ecosystem, we can still find plants having C3, C4, and CAM photosynthetic strategies (Fig. 2 & Fig. 3) [123]. C3 photosynthesis is more prominent across the plant kingdom; hence, there are also xerophytic plants with C3 photosynthetic activities [124]. However, net carbon gain in C3 photosynthesis in desert plants is drastically affected due to photorespiration; hence, desert plants prefer C4 and CAM (usually stomata open at night) photosynthesis [125], [126], [127], [128]. During the cool period of the desert ecosystem, the possibility of photorespiration is minimal, and hence the desert plants conduct photosynthesis via the C3 pathway. The C4 pathway is costly, as it requires two additional ATP to fix the CO₂ (Fig. 3) [129]. In the C4 process, the phosphoenol pyruvate carboxylase (PEP) enzyme in the mesophyll cells of the plant catalyzes the photosynthetic reaction and reduces CO₂ to produce a four-carbon-containing oxaloacetate molecule [130], [131]. Later, the oxaloacetate diffuses from the mesophyll cells to the bundle sheath cells via plasmodesmata and undergoes decarboxylation (Fig. 3) [132], [133]. Therefore, PEP carboxylase serves as the CO₂ pump and supplies CO₂ to the bundle sheath [134]. Although it is a bit costly, still desert plant prefers the C4 pathway to avoid photorespiration [135]. Therefore, we can witness C4 plants in the desert where there is high light and high temperature with an abundance of water. The water use efficiency of the C4 plant is a bit higher compared to other plants [134]. Because C4 plants maintain higher cellular CO₂ level with regard to relative stomatal conductance [136]. The high water requirement for C4 plants becomes a challenging factor in the desert environment, and a deficit in water content leads to the death of the plants. As two additional ATPs are required to reduce CO₂ molecule in C4, the quantum yield of light-use efficiency must be lower in C4 plants than in the C3 counterpart. The CAM plants where CO₂ molecules are stored in malic acid give a significant advantage towards such unusual adaptation [134], [137]. Although the CAM photosynthetic activity is similar to C4 plants, temporal separation of two PEP carboxylase enzymes occurs in the CAM process. However, both reaction occurs in the same cell. In CAM plants, the stomata open in the evening, and CO₂ gets fixed as malate (C4) (Fig. 3) [134]. The malate gets stored in the vacuole of the photosynthetic cells [138]. During the day, the stomata remain closed, and malate gets decarboxylated to release CO₂ [139]. This higher CO₂ level remains inside the cell and cannot diffuse out due to the closed stomata. Rubisco uses this opportunity to operate within a high CO₂/O₂ environment and eliminate the possibility of photorespiration. Thus, the temporal separation of two carboxylases with the Rubisco during the day and PEP carboxylase activity during the night [134]. However, the malic acid content in CAM (cactus) plants remains higher at late night and early morning that is subsequently converted to sugar by afternoon. The C3 and C4 pathways also critically regulate stomatal development and movement. In stress conditions, they close the stomata to avoid loss of water via transpiration. The calcium-signaling event play critical role as an early signaling molecule to activate the mitogen-activated protein kinase (MAPK) pathway that subsequently activate abscisic acid (ABA) biosynthesis (Fig. 4). The ABA directly regulates the stomatal closure via modulation of transcription factors and synthesis of stress-regulated proteins (Fig. 4). Further, Ca²⁺ and ABA signaling regulate the K⁺ ion channel and SLAC1 pathway to close the stomata (Fig. 4). In the absence of stress conditions at night, CRY1/2, Phot1, and other proteins help to open the stomata. More specifically, Cry1 inhibits the production of cGMP (cyclic guanine monophosphate) leading, to the opening of the stomata (Fig. 4).

Fig. 2.

Photosynthetic adaptation strategy of desert plants. Schematic representation of CAM metabolism in desert plants. During the night, stomata remain open in the CAM plants. CO₂ enters the cell and gets stored in the vacuole in the form of four carbon-containing malic acids. During the daytime, the plant's stomata get closed, and stored malic acid is transported to the chloroplast and converted back to CO₂. The resultant CO₂ gets used to carry out photosynthesis during the daytime.

Fig. 3.

Schematic of C4 photosynthetic pathway in xerophytes. Phosphoenol pyruvate and CO₂ in the mesophyll cell get fixed with the help of phosphoenol pyruvate carboxylase to give rise four carbon containing oxaloactic acid (OAA). OAA subsequently reduced to form malate and diffuse to bundle sheath and undergoes decarboxylation to form CO₂-rich environment and thus reduces the photorespiration.

Fig. 4.

Stress avoidance strategy of desert plants through stomata opening and closure mechanism. Upon drought and heat stress exposure, cells receive the stress signal via the calcium signaling pathway. The spiked calcium signature later activates mitogen-activated protein kinases (MAPK). MAPKs later lead to the biosynthesis of abscisic acid (ABA). The cellular ABA activates the transcription factors in the nucleus to produce stress-regulated proteins. These stress-regulated proteins send the signal to the cell to close the stomata to avoid stress. The spike in ABA and Ca²⁺ leads to the block of the K⁺ ion channel, which leads to the stomatal closing. Slow anion channel 1 (SLAC1) effluxes Cl- ion and causes membrane depolarization via KCl and H₂O efflux leading to a reduction in the turgor pressure and stomatal closure. Further, the chloroplast’s photosystem II (PSII) releases reactive oxygen species and sends a signal to close the stomata to avoid excess water loss. CRY1/2 helps for stomatal opening and its development. Also, the Phot1 protein helps in the blue light-mediated stomatal opening. Without stress, the plant keeps the stomata open through the action of CRY1/2 proteins. Protein phosphatase 1 (PP1) and its regulatory subunit PRSL regulate H⁺ ATPase to release H⁺ ions to maintain the stomatal opening. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The C4 photosynthesis is reported to be an evolutionary solution to the high rates of photorespiration and low kinetic efficiency of Rubisco enzyme in CO₂ depleted environment [140]. As photorespiration does not occur in the C4 and CAM plants, the light-use efficiency remains constant upon the increase in the temperature. There are approximately 7500 species having C4 and 30,000 species having CAM photosynthesis. Almost all of the C4 species belonged to the advanced angiosperm group. Bermuda grass, Zoysia graas, Bufallo grass, and Augustine grasses are the classic example of C4 plants commonly found in arid environment. The C4 plants strongly dominated over warm temperate to tropical grasslands and dunes. Approximately, 30% of the terrestrial productivity is contributed by the C4 plants, which is quite higher than the species number [141]. In warm temperate regions, the C4 plants are reported to contribute over 80% of the primary productivity [142].

Genomic makeup of desert plants

Genomics is one of the most important fields of study that enables us to understand the role of different genes associated with a particular trait or sometimes multiple traits. The genomics strategy of desert adaptation is a rapidly growing research area and researchers are trying to find several responsible genes underlying stress adaptation. Sometimes, the stress adaption of plants is shared by various organisms that share similar genomic and molecular stress challenges. Using the population genomics approach of desert plants, population-specific natural selection can be deduced. It will require genome-wide sequencing or high-density SNP (single nucleotide polymorphisms) calling to detect the variations. SNPs are being used to identify genomic regions with high variation of allelic frequency between the populations. These methods can be useful when the background genome-wide differentiation between the desert plants and non-desert plants is relatively low. These principles can be able to detect the specific variants targeted by the selection that is still segregated in the desert population. Other methods can be used to identify the genomic region of reduced diversity, increased haplotype homozygosity, and skewed allelic frequency distribution [143], [144]. When all the populations of a species are descended from a common desert-adapted ancestor, the population-based method may not be helpful in identifying genomic regions associated with the desert adaptation. A comparative genomic study can be very helpful in this regard where a trait-specific desert adaptation can be found by comparing them to a non-desert adapted divergent but related species. The increase in nonsynonymous-synonymous substitution (dN/dS) rate in desert species reflects their positive selection towards desert adaptation [145], [146]. Identification of gene copy numbers between the related species can be another suitable approach to identifying essential genes associated with desert adaptation. Genome-wide association studies (GWAS) can be precious in identifying desert adaptive phenotype variants at the genetic level by identifying the variants reflecting specific traits of interest. Linking phenotype to the genotype becomes a challenging task for the selection studies when to mutation of candidate genes/traits undergoes segregation within the population [147]. Further, transcriptomics can be a complementary study for comparative genomics to identify tissue and species-specific genes associated with adaption to desert ecosystems. Comparative transcriptomics from desert-adapted and non-desert-adapted plants can be very valuable to identify the genes related to desert adaptation.

To understand more and more about the genomic strategy of adaptation of desert ecosystem, it is highly advisable to conduct complete genome sequencing of desert-adapted plants. So that we will be able to uncover important genomic trait/loci responsible to withstand the harsh environment. The genome sequence of a few desert-adapted plants has already been reported (Table 1). They are Welwitschia mirabilis [148], Linathus parryae [149], Prosopis cinera [150], and others (Table 1). Welwitschia mirabilis is a desert plant with extreme longevity with two ever-elongating leaves. A chromosomal-level genome assembly of W. mirabilis is reported, and it was found that W. mirabilis encodes 6.8 gigabytes of genome (estimated 7 Gb) [148]. It was reported that W. mirabilis genome was shaped by lineage-specific ancient whole genome duplication around 86 million years ago [148]. The genome was found to contain the signature peak of duplicated genes with Ks (synonymous substitution) value near 1. At least 198 pair paralogous genes were detected when compared to the genome of Gnetum [148]. The majority of the genome is filled with repetitive elements of long terminal repeat-retrotransposons (LTR-RTs) distributed all over the chromosomes with no indication of the position of the centromeric and subtelomeric region [148]. However, around 1–2 million years ago, the genome got enriched by retrotransposons [148]. The GC content of W. mirabilis was reported to be 29.07%, suggesting the change in nucleotide landscape since the time of divergence [148]. The majorities of the desert inhibiting plants are found to contain low GC content (Table 1). Although W. mirbailis is GC poor plant, it is also characterized by the presence of a high level of cytosine methylation at the CHH motif of the retrotransposons [148]. The methylation reached up to 78.32% and 76.11% in stem and leaf, respectively [148]. The plant also shows tissue-specific methylation, and it occurred in more than 97% of the intergenic region, and from them, 89% occurred in the transposable elements [148]. However, methylation was reported to be lower in the leaves, which seems quite surprising as stress-exposing parts usually undergo hypermethylation to avoid the stress conditions. The genes associated with the methylation pathway, RNA-directed DNA methylation (RdDM) also show upregulation. The upregulation was more prominent in the basal meristem compared to the leaves. The majorities of the genes involved in this pathway are NRPD4 (Nuclear RNA polymerase D4), RDR2 (RNA-dependent RNA polymerase 2), DCL2 (Dicer-like 2), DCL3, DCL4, and DRM2 (Domain rearranged methyltransferase 2). The W. mirabilis genome also showed an increase in 21 and 24 nucleotides of small interfering RNA (siRNA) in basal meristem [148]. The species also showed long-term deamination in the GC-poor region. For the plant W. mirabilis, the epical shoot meristem dies at the early stage shortly after the appearance of the true leaves. During this time, the meristematic activity of the plant moves to the basal meristem. The basal meristem generates the two long-lived strap-like fibrous leaf that shows determinate growth [148]. The most well-known ARID (AT-rich interaction domain) protein comes from the desert plant [151]. However, the role of these proteins is reported more in animals compared to plants [151]. But, the presence of the ARID (A-T rich interaction domain) motif was also reported in A. thaliana although it present outside the ARID region [151]. The transcriptome analysis of Zygophyllum xanthoxylum revealed the role of heat-shock, PS (photosystem I) and PSII (photosystem II) proteins in thermotolerance [152]. Heat treatment in Z. xanthophylum leads to increase in Chl (chlorophyll) a and Chl b production with simultaneous increase in photosynthetic and transpiration rate and stomatal conductance [152]. Transcription factor HSF (heat shock factor), bHLH (basic helix-loop-helix), AP2/ERF (APETALA2/Ethylene response factor), bZIP (basic leucine zipper domain), MYB (myeloblastosis), and WRKY were differentially expressed upon heat stress [152]. Transcriptome analysis of desert plant Cistanthe longiscapa, a drought tolerant plant of Atacama desert revealed the role of genes involved in abscisic acid signaling and circadian rhythm [153].

Table 1.

2n genome size of a few xerophytic desert species [160], [161]. The genome size varies from small to intermediate. The maximum of desert inhibiting plants contain lower GC%.

Species name	Genome size (Mb)	GC%
Acacia acuminate	1760.18	35.30
Acacia melanoxylon	1498.22	35.40
Acacia pycnantha	1630.82	36.10
Agave deserti	17,320	35.69
Anastatica hierochuntica	1084.686	37.40
Asparagus kiusianus	3237.74	36.10
Boswellia sacra	1335.678	31.60
Bursera cuneata	505.8	34.70
Carnegiea gigantea	2807	36.10
Calotropis procera	418.43	20.00
Cereus fernambucensis	1824.36	35.80
Cissus quadrangularis	563.408	27.10
Corchorus olitorius	669.798	35.50
Datura stramonium	4220.92	29.20
Euphorbia esula	1278.04	37.10
Euphorbia peplus	534.392	35.23
Ficus carica	666.88	34.40
Ficus erecta	1191.67	34.30
Ficus hispida	739.506	34.56
Ficus microcarpa	853.126	34.34
Ficus religiosa	812.206	32.40
Fraxinus velutina	1304.598	34.90
Gossypium harkensii	1464.3	34.17
Kalanchoe fedtschenkoi	512.702	34.50
Linanthus parryae	3028.98	40.10
Mimosa pudica	1114.404	32.90
Papaver californicum	2744.82	33.70
Plantago ovata	1001.878	38.39
Phoenix dactylifera	908.734	35.70
Prosopis alba	1414.324	34.30
Prosopis cinera	1382	32.08
Punica granatum	640.988	40.36
Rhazya stricta	548.708	32.90

A study conducted with Atacama desert plants to identify the adaptive stress genes, it was found that the stress-responsive genes of Atacama desert plants were linked to the positive selection pressure of their environment [1]. The genes involved in DNA damage, reactive oxygen species, response to light stimuli, light reaction, and plastid organization are related to extreme high-light radiation in Atacama [1]. The genes involved in stress adaptation, reactive oxygen species generation and homeostasis, salt stress, metal ion stress, and nutrient metabolism (N, P, and S) could be associated with adaptation to these plants. A few of the genes associated with solar radiation are LARP1 (La ribonucleoprotein 1), POX (peroxidase) (APX2) (ascorbate peroxidase 2), LSD1 (lysine-specific demethylase 1), PEXIIE (peroxisomal biogenesis factor IIE), EX1 (executor 1), PHR2 (photolyase receptor 2) (Fig. 5, Table 2); genes associated with photosynthesis are JAC1 (J-type co-chaperon 1), CP31A (chloroplast RNA binding protein 31A), MRL1 (mannose 6-phosphate receptor 1), EGY1 (ethylene-dependent gravitropism-deficient and yellow-green 1), MDA1 (MTERF defective in Arabidopsis 1), CP24 (chlorophyll a-b binding protein 24), PnsL4 (photosynthetic NDH subunit of lumenal location 4), RBCS1A (ribulose 1,5-biphosphate carboxylase/oxygenase synthase 1A), and GDCH (glycine decarboxylase complex, H-subunit) (Table 2); genes associated with water capture are DTX35 (detoxifying efflux carrier 35), NTL9 (NAC transcription factor like 9), NF-YA10 (nuclear factor Y A10), MYB52, AtARRE (Arabidopsis thaliana ABA-related ring-type E3 ligase), and TIP1.1 (tonoplast intrinsic protein 1.1) (Table 2); genes associated with root growth are ZP1 (zinc finger protein 1), GET1 (guided entry of tail-anchored proteins1), LRX1 (leucine rich extension protein 1), and RHL1 (root hairless 1) (Table 2); genes associated with nutrient use efficiency are ZAT6 (zinc finger transcription factor of Arabidopsis thaliana), TAR2 (tryptophan aminotransferase related 2), WRKY1, PAP26 (purple acid phosphatase 26), HGML (3-hydroxy-3-methylglutaryl-CoA lyase), and APK (adenyly sulfate kinase 2) (Table 2); genes involved in flowering time are SHL (seedling hyperresponsive to light), BIC1 (blue-light inhibitor of cryptochromes 1), CRY2 (cryptochromes 2), SOC1 (suppressor of overexpression of CO1), FLR1 (Feronia-like receptor 1), SWEET10, VAL1 (viviparous/abscisic acid insensitive3-like 1), VIP4 (vernalization independence 4), CIB1 (cryptochrome-interacting basic-helix-loop-helix 1), and AP2 (apetala 2) (Table 2). The transcription factors WRKY, MYB, ZAT, and others bring altered gene expression and play a critical role in stress tolerance by regulating root development in plants (Fig. 6). The transcription factors WRKY, MYB, ZAT and others bring altered gene expression and play a critical role in stress tolerance by regulating plant root development (Fig. 6). Transcription factor-mediated gene expression also brings biochemical changes and produces stress-responsive chemicals mannitol, proline, sorbitol, glycine, and others. The production of these metabolites also help to regulate plant development through production of short internodes that minimizes the surface area of the plants.

Fig. 5.

Mechanism of stress tolerance in desert plants. The downstream signaling system, including abscisic acid (ABA), calcium, reactive oxygen species, and the jasmonic acid signaling system, gets activated upon stress response. ABA signaling led to the activation of ion channels via PRY, PP2C, and SnRK2 genes. Further, Ca²⁺ ion provides an added response to the ion channel activation. Response to ion channel activation led to the stomatal closure for stress tolerance. Similarly, Ca²⁺ ion signaling acts via calcium-dependent protein kinase, interacts with the mitogen-activated protein kinase pathway, and brings downstream signaling to activate the nuclear-encoded genes. High jasmonic acid production due to stress led to protein degradation in 26S proteasome via SCF, Col, and JA-Ile. It also activates MYC2 genes to regulate stress in plants. NADPH-mediated signaling leads to the production of oxygen-free radicals, H₂O₂, and OH-free radicals. The H₂O₂ gets catalyzed by catalase to produce H₂O and O₂. Using catalase and peroxidase, plants can bring free radical-mediated cellular homeostasis and protect the cell from oxidative damage.

Table 2.

List of genes associated with abiotic stress tolerance in desert ecosystem.

Genes	Functional property	Ref
Solar radiation
LARP1	mRNA cap binding protein that controls ribosome biogenesis. Induces leaf senescence. Response to abiotic stress and hormone stimulation.	[1], [162], [163]
APX2	High light and drought stress.	[1], [164]
LSD1	Negative regulator of plant cell death.	[1], [165]
PEXIIE	Pixie gene with natural mutation shortens the internodes and helps flowering. Helps in dwarfism.	[1], [166]
EX1	Mediates singlet oxygen induced program cell death.	[1], [167]
PHR2	Blue light photo receptor. Photolyase.	[168], [169]
Improvement of Photosynthesis
JAC1	Has positive effect on water use efficiency, reduction of stomatal aperture. Water vapor conductance. Fine tuning of H2O2 level, control cell death.	[170]
CP31A	Involved in chloroplast RNA processing steps. Editing and stability of chloroplast mRNA.	[171], [172]
MRL1	Helps to stabilize RBCL gene.	[173]
EGY1	Chloroplast development in epidermal guard cells. Plastid size and number. Abscisic acid signaling.	[174], [175], [176]
MDA1	Chloroplast embedded abiotic stress responsive gene.	[177]
CP24	Antenna protein that play crucial role between photosystem II subunit and electron transport rate in grana membranes. Maintain structure and function of grana membrane.	[178], [179]
PnsL4	Associated with chloroplast NADH dehydrogenase-like complex.	[180]
RBCS1A	Associated with Rubisco content and drought stress.	[181], [182]
GDCH	Reactive oxygen species induced leaf senescence, photorespiration.	[183], [184]
Water Capture
DTX35	Helps in drought tolerance.	[185]
NTL9	Osmotic stress signaling and regulation of osmotic stress.	[186]
NF-YA10	Drought resistance and salinity stress response.	[187], [188]
MYB52	Abiotic stress response, ABA hypersensitivity & drought tolerance.	[189], [190]
AtARRE	Negatively regulates ABA signaling.	[191]
TIP1.1	Aquaporin gene involved in plant cell death and abiotic stress tolerance.	[192], [193]
Root growth
ZP1	Repression of root hair formation.	[194]
GET1	Involved in root elongation.	[1]
LRX1	Cell wall formation during root hair development, root hair morphogenesis, TOR signaling.	[195], [196], [197]
RHL1	Root hair initiation and development, Ploidy-dependent cell growth.	[198], [199], [200]
Nutrient Use Efficiency
ZAT6	Phosphate homeostasis, transcriptional regulation of phosphate starvation.	[201]
TAR2	Nitrogen mediated reprogramming in root. Auxin biosynthesis.	[202], [203]
WRKY1	Function as H+-ATPase. Response to Zn deficiency.	[204], [205]
PAP26	Nutritional phosphate starvation, delay senescence due to phosphate starvation.	[206], [207]
HGML	Abiotic stress response, response to dehydration stress.	[1], [208], [209]
APK	Sulphate assimilation, osmotic stress.	[210], [211], [212]
Regulation of flowering time (early)
SHL	Plant fertility, repression of flowering.	[213], [214]
BIC1	Transcriptional coactivator.	[215]
CRY2	Floral initiation.	[216], [217]
SOC1	Regulation of flowering pathway, enhance flowering and yield.	[218], [219]
FLR1	Plant flowering and fertility.	[220], [221]
SWEET10	Early flowering.	[222]
VAL1	Regulates floral transition.	[223], [224]
VIP4	Activator in flowering, regulation of flowering time genes.	[225]
CIB1	Regulate CRY2 mediated flowering, transcriptional floral initiation, photoperiodic flowering.	[216], [226], [227], [228]
AP2	Associated with flowering and seed development, floral organ development.	[229], [230]

LARP1: La ribonucleoprotein 1, APX2: ascorbate peroxidase 2, LSD1: lysine-specific demethylase 1, PEXIIE: peroxisomal biogenesis factor IIE, EX1: executor 1, PHR2: photolyase receptor 2, JAC1: J-type co-chaperon 1, CP31A: chloroplast RNA binding protein 31A, MRL1: mannose 6-phosphate receptor 1, EGY1: ethylene-dependent gravitropism-deficient and yellow-green 1, MDA1: MTERF defective in Arabidopsis 1, CP24: chlorophyll a-b binding protein 24, PnsL4: photosynthetic NDH subunit of lumenal location 4, RBCS1A: ribulose 1,5-biphosphate carboxylase/oxygenase synthase 1A, GDCH: glycine decarboxylase complex, H-subunit, DTX35: detoxifying efflux carrier 35, NTL9: NAC transcription factor like 9, NF-YA10: nuclear factor Y A10, MYB52: myeloblastosis, AtARRE: Arabidopsis thaliana ABA-related ring-type E3 ligase, TIP1.1: tonoplast intrinsic protein 1.1, ZP1: zinc finger protein 1, GET1: guided entry of tail-anchored proteins1, LRX1: leucine rich extension protein 1, RHL1: root hairless 1, ZAT6: zinc finger transcription factor of Arabidopsis thaliana, TAR2: tryptophan aminotransferase related 2, PAP26: purple acid phosphatase 26, HGML: 3-hydroxy-3-methylglutaryl-CoA lyase, APK: adenyly sulfate kinase 2, SHL: seedling hyperresponsive to light, BIC1: blue-light inhibitor of cryptochromes 1, CRY2: cryptochromes 2, SOC1: suppressor of overexpression of CO1, FLR1: Feronia-like receptor 1, VAL1: viviparous/abscisic acid insensitive 3-like 1, VIP4: vernalization independence 4, CIB1: cryptochrome-interacting basic-helix-loop-helix 1, AP2: apetala 2.

Fig. 6.

The stress adaptation strategy of desert inhibits plants via physiological, morphological, biochemical, and molecular responses. During stress response (e.g., light), physiological changes reduce leaf turgor pressure and stomata closure. Closure of stomata leads to reduced CO2 assimilation. Reduced assimilation propagates Rubisco photorespiration leading to the generation of several stress-tolerant chemicals, including glycine, proline, sorbitol, mannitol, and others. The biosynthesis of these chemicals helps in drought tolerance. The stress response also leads to the generation of phytohormone abscisic acid, calcium signaling, and reactive oxygen species generation, allowing stomata to be closed. Morphological response, including leaf rolling, leaf abscission, deep root system, and short internodes, comes into play due to stress events through the molecular action of transcription factors/altered gene expression.

Evolutionary aspects of desert plants via C4 and CAM metabolism

The C4 and CAM photosynthesis are reported to evolve from C3 photosynthesis. However, various biochemical modifications required to conduct C4 or CAM might have evolved independently in different plant taxa. As life may have evolved from the ocean, it is believed that C4 photosynthesis evolved in response to the low concentration of CO₂ in the atmosphere during Cretaceous period. The reduced level of atmospheric CO₂ might lead to higher photorespiration in C3 plants, thus reducing their productivity. However, it can be noted that the evolution of CAM might have occurred in response to increased-water use efficiency. The C4 photosynthesis seems to be a recent phenomenon that goes back to approximately 12–15 million years ago. The study also reported the presence of C4 grass around 15 million years ago in East Africa [140]. The molecular clock hypothesis indicates the C4 plants might have evolved around 20 to 35 million years ago [154]. However, the ecological dominance of the C4 plants occurred around 7 to 8 million years ago and might have evolved simultaneously across different parts of the world [155]. Earlier, it was reported that the atmospheric CO₂ of the earth was higher compared to the present. According to the geochemical carbon balance model, the atmospheric CO₂ level during Triassic, Jurassic, and Cretaceous might contain CO₂ content five to eight times greater than today [156], [157], [158]. According to the model, the atmospheric CO₂ dropped from a range of 2800–1400 to below 1000 µL L^-1 in the Eocene, Miocene, and Pliocene. It is hypothesized that reduction in the atmospheric CO₂ level led to favor of the evolution of C4 photosynthesis [159].

Conclusion

Plant surviving in the desert have unique physiology and biochemical abilities. For example the enhancement in the stem photosynthesis adopted by desert plants can be applied to the crop plants to withstand adverse dry and drought conditions minimizing the crop loss due to the stringent drought. In addition, constructing a mathematical model can enable an understanding of the role of the deep root system, and the development of root meristem can highlight more towards the understanding of adaptation to the desert environment. A lot of knowledge can be gained from these desert plants, and Cactus can be one of the classic examples that develop a horizontal root system along with a nodal rain-sensing root system. A horizontal root development system can be of great importance for crop plants. Few roots that grow above the soils show their potential to capture environmental water content through a gravitropic development mechanism. Further, it is also highly necessary to add the genome sequence data of more and more desert-adapted species to understand the genetic and genomic basis of their stress adaptation. A comparative genomic study can be very helpful in identifying stress-adapted traits that can be incorporated into crop plants for stress adaptation. Integration of single-cell omics can be an added advantage as these can enable us to understand the tissue-specific genetic information of stress tolerance.

Understanding the genomic basis of adaptation to the desert environment will be crucial to restoring biodiversity currently threatened by a higher rate of desertification. Establishing the link between desert genotype, phenotype, and environment will be important. It will help us predict species' adaptive strategy towards climate change and their functional traits. The functional traits will be crucial to establish the role of natural selection under arid and drought conditions. Focusing more research on desert plants will enable us to preserve the adaptive genetic pools to cope with the ongoing climate changes.

Compliance with ethics requirements

The study does not include any animal in the experiment. Hence, it is not required.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Biographies

Dr. Tapan Kumar Mohanta is currently working as a researcher at the Natural and Medical Sciences Research Center, University of Nizwa, Oman, from 2018. Dr. Mohanta is working in the field of genomics and molecular aspects of plant and microbial biotic and abiotic stresses. Working in an arid country has given me ample opportunity to work on the physiology, biochemistry, genomics, and molecular aspects of drought adaptation of plants to an arid environment. From 2014-2018, Dr. Mohanta worked as a Research Professor at Yeungnam University, South Korea, and completed his postdoctoral research at the National Institute of Plant Genome Research, India, and G.B. Pant University of Agriculture and Technology, India. Dr. Mohanta has more than ten years of post-PhD research experience with 87 SCI-indexed, 11 non-SCI indexed and seven book chapters (total 105). Dr. Mohanta has more than 3600 citations with h-index 29 and i-10 index 52. Dr. Mohanta works as an associate editor in nine-reputed peer-reviewed journals, including Scientific Reports, Frontiers in Mol. Bio. Sci., Frontier in Ecology and Evolution, Frontiers in Microbiology, Mitochondrial DNA Part B, BMC Genomic Data, BMC Research Notes, Current Proteomics, and Current Protein and Peptide Science. According to Stanford University Survey, Dr. Mohanta is listed among the top 2% of highly cited researchers globally, having overall ranking of 71532 in all field and 78 rank in Plant Biology & Botany. I have peer-reviewed at least 26 different scientific journals of international repute. Also, according to the loop profile, Dr. Mohanta possesses more publications than 97% of the authors listed in the loop (top 3% highest publication holder). Dr. Mohanta has reported several novel discoveries so far in his field of expertise

Dr. Yugal Kishore Mohanta is now working as Assistant Professor at the Department of Applied Biology, School of Biological Sciences, University of Science and Technology, Meghalaya (USTM), India, Accredited “A” Grade by NAAC. Very recently, before the COVID-19 pandemic emergency, Dr. Mohanta was working as visiting researcher at Biotechnology and Omics Laboratory, Natural and Medical Sciences Research Centre, University of Nizwa, Sultanate of Oman. His current research interest is in Metal/Composite nanoparticles and their potential for application in plant abiotic stress. He completed his Ph.D. in Life Sciences from North Orissa University, Baripada in 2019. Among other academic/research achievements, he was awarded as visiting research scholar at the Department of Biology, KU Leuven, Belgium, sponsored by KU Leuven. He has more than twelve years of post-M.Sc. research experience in natural products chemistry, metal nanoparticles, and plant stress. He has published 54 papers in peer-reviewed SCI indexed journals of international and national reputes with high impact factors having 1068 citations and an h-index of 16 and an i10 index of 24, and Reviewers of more than 20 international peer-reviewed journals and Associate editors in 4 international peer-reviewed journals. He has also contributed 12 book chapters, edited a book in CRC Press, and written many popular science articles in national science magazines. He is a gold medallist in his bachelor’s and Master's Degrees.

Dr. Prashant Kaushik is a researcher at Chaudhary Charan Singh Haryana Agricultural University, Haryana, India. He holds a BS (Hons) in agriculture, a PG diploma in floriculture and landscaping, an MS in vegetable science, and an MBA in production and operations management. After obtaining a PhD in biotechnology from Universitat Politecnica de Valencia, Spain, Dr. Kaushik was a bioinformatician researcher at Nagano University in Ueda, Japan and at Yokohama Ueki in Kikugawa City, Japan. Dr. Kaushik has published 36 SCI or SCI-E indexed research articles. He has written 2 books and 10 book chapters. His research interests include molecular biology, plant breeding, genomics, and population genetics.

Jitesh Kumar obtained his doctoral degree from National Agri-Food Biotechnology Institute (NABI), Mohali, and Panjab University Chandigarh, India. He investigated the prevalence and pathogenesis of the wheat dwarf India virus and utilized it for gene silencing. His group demonstrated using CRISPR/Cas9 for genome editing in model plants and crops from India. He is establishing precise genome modifications using CRISPR/Cas9 at a high-throughput platform for sustainable agriculture at the University of Minnesota, Twin Cities, USA. Dr. Kumar is also a recipient of the EMBO-Travel grant, a Postdoctoral grant from CSIR-India, ARO-Israel, and SERB-N-PDF-India. Dr. Kumar is an editorial board member of BMC's Plant Biology and BMC Biotechnology and reviewing various peer review journals; Frontiers in Plant Science, Plant Physiology and Biochemistry, Journal of Plant Growth Regulation (JPGR), and Journal of Advanced Research (JARE).