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Plant science’s next top models (Review)

Annals of Botany 126: 1–23, 2020

doi: 10.1093/aob/mcaa063

Model organisms are used in research to answer biological questions in a living organism. Such models are simple, both biologically and in handling, making them suitable for laboratory work. In plant science, the thale cress Arabidopsis thaliana has been used as a model since the 1980s. However, plant science has advanced to a point where increasingly complex traits and processes, which may not be present in Arabidopsis, can be studied as well. For this, new model plants with additional features of interest are needed. Cesarino et al. highlight seven of these models and describe the questions that they will help answer.

Authors: Igor Cesarino, Raffaele Dello Ioio, Gwendolyn K. Kirschner, Michael S. Ogden, Kelsey L. Picard, Madlen I. Rast-Somssich, and Marc Somssich

Nepenthes photosynthesis under different nutrient application

Annals of Botany 126: 25–37, 2020

doi: 10.1093/aob/mcaa041

Carnivorous plants can enhance photosynthesis in response to prey nutrient uptake; however, the underlying mechanisms of increased photosynthesis are largely unknown. Capo et al. investigate the photosynthetic response of both root-fertilized and insect-fed nutrition in the pitcher plant Nepenthes × ventrata. Their results show an investment of the nitrogen acquired from both types of nutrition to photosynthetic apparatus components, such as chlorophyll, pigment–protein complexes and Rubisco. Moreover, after determining the mesophyll conductance to CO₂ for the first time in carnivorous plants, they demonstrate that the equilibrium between the biochemical and mesophyll limitations of photosynthesis is strongly affected by the nutrition treatment.

Authors: Sebastià Capó-Bauçà, Marcel Font-Carrascosa, Miquel Ribas-Carbó, Andrej Pavlovič, and Jeroni Galmés

For a Commentary on this article, see this issue, pp. iv–v.

Seed coat development in explosively dispersed seeds of Cardamine hirsuta

Annals of Botany 126: 39–59, 2020

doi: 10.1093/aob/mcz190

Seeds are dispersed by explosive coiling of the fruit valves in Cardamine hirsuta (Brassicaceae). Important interactions occur at the seed surface during seed launch and subsequent flight. Using light and electron microscopy, Neumann and Hay characterize differentiation of the two outermost seed coat layers in C. hirsuta. They found that both layers are characterized by specialized, pectin-rich cell walls that are deposited asymmetrically in the cell. These cell walls in the subepidermal seed coat layer determine the ridged topography of the seed surface and distinguish C. hirsuta seeds, which are ballistically dispersed, from Arabidopsis thaliana seeds, which are not.

Authors: Ulla Neumann and Angela Hay

Excess nitrate induces nodule greening and reduces leghaemoglobin levels

Annals of Botany 126: 61–72, 2020

doi: 10.1093/aob/mcaa002

Soybean (Glycine max, Fabaceae) fixes approximately 16.4 million tons of N₂ by nodules annually, which represents about 77% of the N₂ fixed by leguminous crops. However, efficient N₂ fixation capacity requires leghaemoglobin (Lb) to modulate oxygen pressure in nodules. Du et al. identify seven haemoglobin genes; GmLb1 to GmLb4 were closely associated with nodule development and N₂ fixation. Excess N significantly accelerated nodule senescence and the production of green Lb in nodules, inhibiting biological nitrogen fixation by reducing nodule formation, Lb concentration and nitrogenase activity.

Authors: Mengke Du, Zhi Gao, Xinxin Li, and Hong Liao

Phylogenomics of Afromontane Podocarpus

Annals of Botany 126: 73–83, 2020

doi: 10.1093/aob/mcaa049

Podocarpus (latifolius–milanjianus complex, Podocarpaceae) is the most widespread conifer in sub-Saharan montane forests. Except in East Africa, most populations are small and isolated, despite palaeobotanical records of abundant podocarps until the mid-Holocene. Migliore et al. use DNA sequencing to reveal that the species underwent an extensive range expansion after c. 200 kyr BP, probably from East Africa, and reached as far as the highlands of the Atlantic side of Africa. Hence, Afromontane forests were once very widespread and continuous, before their recent fragmentation. This highlights the striking ability of podocarps not only to persist locally in various ‘sky islands’ refugia but also to migrate quickly during suitable environmental conditions.

Authors: Jérémy Migliore, Anne-Marie Lézine, and Olivier J. Hardy

Evolution of Indeterminate Domain (IDD) transcription factors

Annals of Botany 126: 85–101, 2020

doi: 10.1093/aob/mcaa052

Indeterminate Domain proteins (IDDs) are a plant specific subclass of C₂H₂ Zinc Finger transcription factors. Some of these transcription factors play roles in diverse aspects of plant metabolism and development, however the function of most of IDDs is unknown and their molecular evolution has not been explored. Prochetto and Reinheimer reconstruct the evolution of IDDs during plant land conquest. They found that IDDs arose from the common ancestor of Streptophyta. Once on land, IDDs experienced a rapid radiation that accompanied the key morphological, physiological and biochemical transitions required in plant terrestrialization. Prochetto and Reinheimer present a solid phylogenetic framework of annotated IDD genes which links genetic and functional knowledge from model to non-model species.

Authors: Santiago Prochetto and Renata Reinheimer

Arabis scabra, a Mediterranean element in the north-western Atlantic region

Annals of Botany 126: 103–118, 2020

doi: 10.1093/aob/mcaa053

Arabis scabra (Brassicaceae), a short-lived perennial herb, restricted to limestone, is one of the few plant species in the British Isles considered as having Mediterranean-montane element. Koch et al. genotyped accessions with different molecular markers from its distribution range—also exemplifying the value of herbarium collections. They demonstrate that the species has expanded its distribution range after the Last Glacial Maximum by following corridors within an open landscape, and may have reached the British Isles via the desiccated Celtic Sea about 16 000 years ago. The study sheds light on the origin of other rare and peculiar species co-occurring in limestone regions in the southwestern British Isles.

Authors: Marcus A. Koch, Johanna Möbus, Clara A. Klöcker, Stephanie Lippert, Laura Ruppert, and Christiane Kiefer

Genetic dissection of the shoot and root ionomes of Brassica napus

Annals of Botany 126: 119–140, 2020

doi: 10.1093/aob/mcaa055

Very little is known about the molecular determinants of alterations in the ionome caused by fluctuations in phosphorus (P) supply. Wang et al. identify a total of 256 chromosomal quantitative trait loci (QTLs) for shoot and root ionomic traits in a Brassica napus double haploid population grown with contrasting P supplies in an agar system. A major QTL cluster on chromosome C07 had a significant effect on shoot Mg and S concentrations at LP and was narrowed down to a 2.1-Mb region using an advanced backcross population. The tissue concentration and partitioning of each mineral element was affected differently by phosphorus starvation. There was a significant difference in mineral element composition between shoots and roots.

Authors: Wei Wang, Guangda Ding, Philip J. White, Meng Wang, Jun Zou, Fangsen Xu, John P. Hammond, and Lei Shi

Leaf cuticle analyses: implications for the existence of cutan

Annals of Botany 126: 141–162, 2020

doi: 10.1093/aob/mcaa056

The cuticle of some of plant species contains cutan, a highly resistant biopolymer. Attempting to unravel its origin, Leide et al. analyse the chemical composition of enzymatically isolated cuticular membranes. The cuticular waxes, cutin and cutan of Agave americana, Clivia miniata, Ficus elastica and Prunus laurocerasus leaves were examined by gas chromatographic analyses. The residual cutan matrix was analysed by thermal extraction, flash pyrolysis and thermally assisted hydrolysis and methylation. The high similarity of aliphatic moieties of cuticular waxes and cutan monomers indicated a common biosynthetic origin. There were compositional and structural differences between species, and cutan was only found in leaves of the perennial evergreen A. americana and C. miniata.

Authors: Jana Leide, Klaas G. J. Nierop, Ann-Christin Deininger, Simona Staiger, Markus Riederer, and Jan W. de Leeuw

Population genetics of a dwarf plant

Annals of Botany 126: 163–177, 2020

doi: 10.1093/aob/mcaa062

Plant dwarfism has been well documented as an evolutionary syndrome in stressful environments, but its genetic consequences are poorly understood. Sakaguchi et al. investigate genetic characteristics of the world’s smallest goldenrod, Solidago minutissima (Asteraceae), in the alpine zone of Yakushima Island of Japan, to find a pronounced level of genetic isolation among dwarf populations. Demographic modelling inferred that gene flow has been at non-significant levels since the establishment of populations of dwarf specimens. Their low-growing stature (ca. 2.6 cm height) and reduced fecundity (3.1 heads per stem) may have reduced long-distance seed dispersals among habitat patches, which are only approximately 500 m apart.

Authors: Shota Sakaguchi, Atsushi J. Nagano, Masaki Yasugi, Hiroshi Kudoh, Naoko Ishikawa, and Motomi Ito

Stomatal responses to increased CO₂ concentration

Annals of Botany 126: 179–190, 2020

doi: 10.1093/aob/mcaa065

Increased CO₂ concentration induces partial stomatal closure in most plants, resulting in reduced water use. However, the magnitude of this response shows a large variation among species and ecotypes. Johansson et al. study the stomatal CO₂ response in arabidopsis on different time scales to gain insights about the genetic basis for this variation and investigate whether short-term experiments can predict long-term CO₂ effects. They identify a genetic component associated with responses on both time scales and find a robust relationship between short- and long-term responses. This highlights the value of short-term experiments on model plants in climate change research. Photo: Kaspar Koolmeister.

Authors: Karin S. L. Johansson, Mohamed El-Soda, Ellen Page, Rhonda C. Meyer, Kadri Tõldsepp, Anders K. Nilsson, Mikael Brosché, Hannes Kollist, Johan Uddling, and Mats X. Andersson

The protected tree Dimorphandra wilsonii is a population of inter-specific hybrids

Annals of Botany 126: 191–203, 2020

doi: 10.1093/aob/mcaa066

Dimorphandra wilsonii (Fabaceae) is a protected tree with a National Plan of Action for its conservation. It co-occurrs with two other Dimorphandra species, D. mollis and D. exaltata, in a savannah/forest ecotone in southeastern Brazil. Muniz et al. find that D. wilsonii is a hybrid population dominated by F1 individuals and that it originated from hybridization between D. exaltata and D. mollis. They suggest that the conservation and management strategy of D. wilsonii should be re-evaluated and taken into account both parental species. The findings highlight the value of genetic information for the design of conservation strategies.

Authors: André Carneiro Muniz, José Pires Lemos-Filho, Helena Augusta Viana e Souza, Rafaela Cabral Marinho, Renata Santiago de Oliveira Buzatti, Myriam Heuertz, and Maria Bernadete Lovato