Gene drive to control a major crop pest
D. suzukii on a strawberry.
Between 2009 and 2014, spotted wing fruit flies (Drosophila suzukii), virtually ubiquitous invasive crop pests from Japan that attack a variety of soft-skinned fruits, accounted for an estimated $39.8 million revenue loss in California raspberry farms. Anna Buchman et al. (pp. 4725–4730) explored the use of Medea gene drives to complement current pest control measures based on insecticides. The gene drive couples a microRNA toxin, which is expressed in drive-bearing maternal flies during egg formation and targets a gene essential for normal embryo development, to an antidote, which is expressed in drive-bearing progeny and furnishes a toxin-resistant copy of the target gene to embryos. Once linked to Medea, cargo genes, such as those that confer susceptibility to chemical insecticides, spread rapidly through populations of D. suzukii flies because progeny that lack the drive perish. Over six generations of outcrosses of flies under controlled conditions, around 97.7% of progeny from Medea-bearing heterozygous females retained the drive, compared with the 50% rate expected for genes inherited in standard Mendelian fashion. Further, the authors demonstrated similarly biased inheritance using strains of flies collected from diverse locations in the United States and Japan. Mathematical modeling and multigenerational cage experiments, in which drive-bearing flies were mated with a strain with preexisting resistance, revealed that releasing drive-bearing flies at high frequencies could help maintain the drive at rates greater than 75% over approximately 20 generations, which is likely sufficient for agricultural impacts. The findings furnish proof of principle for research efforts aimed at using gene drives to control major crop pests, according to the authors. — P.N.
Photovoltaics, thermal stability, and power conversion
Flexible photovoltaic devices offer a potential solution for supplying electrical power to wearable sensors and electronic devices. However, current flexible organic photovoltaics (OPVs) lack the thermal stability and power conversion requirements to enable the optimal performance of such devices. Xiaomin Xu et al. (pp. 4589–4594) developed an ultraflexible OPV with increased power conversion efficiency (PCE) and thermal stability. The 3-µm-thick device consists of a robust polymer microstructure and an ultrathin plastic substrate and barrier coating that enable high thermal stability. The authors conducted stability and lifetime testing of the OPV in air chambers in which the OPV was exposed to different temperatures. During tests in which the OPV cells were kept at air temperatures of 120 °C and 130 °C, the authors observed decreases of initial PCE of 7.4% and 13.8%, respectively; in comparison, another OPV polymer design exhibited a 37.6% decrease in initial PCE at 130 °C. Moreover, the ultrathin OPV maintained 80% of the initial PCE at over 500 hours of continuous thermal stress at 85 °C. The findings carry implications for power generation for common electronic devices, according to the authors. — C.S.
Using machine learning to examine plant stresses
Plant stresses are typically classified by trained experts who manually identify visual symptoms, a process that is time-consuming, error-prone, and subjective. Sambuddha Ghosal et al. (pp. 4613–4618) developed a machine learning approach to automate the process of identifying, classifying, and quantifying stresses in soybean. The authors trained the deep learning model on approximately 25,000 images of stressed and healthy soybean leaflets, and the trained model rapidly and accurately identified and classified several abiotic stresses, such as herbicide injury and nutrient deficiency, and biotic stresses, such as fungal and bacterial diseases, from images of soybean leaflets. To determine which visual symptoms the model used to make its predictions, the authors extracted high-resolution feature maps learned by the model in an unsupervised manner and correlated the maps with the visual symptoms of each stress identified by human experts. The authors found a high level of agreement between the machine and human annotations. The model also accurately identified stresses in other plant species and under different lighting and imaging conditions, suggesting that the approach could be widely applicable for real-time, high-throughput phenotyping of plant stresses. According to the authors, the deep learning approach could have a variety of applications in plant research, plant breeding, and crop production and management. — S.R.
Tea plant genome reveals insights into tea evolution
C. sinensis. Image courtesy of Wikimedia Commons/AxelBoldt.
Consumed by humans for nearly 5,000 years, tea derives its diverse range of flavors and health benefits from around 700 bioactive compounds. Over the last two decades, researchers have focused on the biosynthesis pathways of naturally occurring compounds in tea, notably catechins, theanine, caffeine, and volatile compounds that confer characteristic aromas and tastes. However, such efforts are hampered by the lack of a tea plant reference genome. Chaoling Wei et al. (pp. E4151–E4158) present a high-quality draft genome sequence for Camellia sinensis var. sinensis, the source of green teas. The genome reveals that C. sinensis branched off from a shared lineage with kiwifruit around 80 million years ago and, along with its sister lineage Camellia sinensis var. assamica, diverged from a common ancestor 0.38–1.54 million years ago. Furthermore, the authors report that a pair of whole-genome duplications at 90–100 million years ago and 30–40 million years ago, as well as subsequent paralogous duplications, gave rise to the gene copies that produce catechins, theanine, and caffeine in tea plants. The findings provide insights into tea genome evolution and might help develop improved tea plant cultivars, according to the authors. — T.J.
Compounds tied to malaria infection increase human attractiveness to mosquitoes
To locate hosts, female Anopheles mosquitoes use volatile compounds released from human skin that contribute to body odor. Previous studies have found that Plasmodium infection increases human attractiveness to mosquitoes, but the underlying skin chemistry remained unexplored. Ailie Robinson et al. (pp. E4209–E4218) report that in a lab assay Anopheles gambiae mosquitoes were more attracted to the foot odor of children who harbored Plasmodium than to the foot odor of the same children collected 21 days after administration of an antimalarial treatment; foot odors were collected on socks from 5- to 12-year-old children in western Kenya. In contrast, the mosquitoes did not distinguish between foot odors of parasite-free children collected at the same pair of time points. Chemical analysis revealed that increased amounts of the skin aldehydes heptanal, octanal, and nonanal in infected children were positively linked with parasite density. Mosquito behavioral analysis under controlled conditions suggested that elevated heptanal levels in Plasmodium-infected children might heighten their attractiveness to Anopheles coluzzii mosquitoes. Adding heptanal to a synthetic mosquito lure that mimics healthy human odor failed to increase its attractiveness. However, adding a blend of Plasmodium infection-associated compounds, including heptanal, to this lure, in an attempt to mimic the odor cues of an infected person, proved attractive to An. coluzzii. According to the authors, the findings could illuminate aspects of malaria transmission, help improve the design of mosquito lures, and lead to the development of novel diagnostic biomarkers for malaria. — P.N.
Electroactive bacteria as a catalyst regulator
Scanning electron micrograph of S. oneidensis MR-1 before polymerization, scale bar: 2 µm.
Metabolic engineering harnesses biological processes to produce molecules of interest, including pharmaceuticals and fuels. To expand the types of reactions amenable to metabolic engineering, Gang Fan et al. (pp. 4559–4564) used the bacterium Shewanella oneidensis to control the activity of copper-based catalysts in a radical polymerization reaction. Although the contents of cells released during lysis could effect the polymerization reaction, the authors found that polymerization rates in cases of lysis were low and that dead intact cells resulted in no reaction, suggesting that the metabolic activity of live cells was responsible for powering the polymerization reaction. The polymer products exhibited a well-defined molecular weight, and using other bacteria such as Escherichia coli produced no significant polymerization. The rate of polymerization was dependent on the carbon source for S. oneidensis and specific electron transport proteins. According to the authors, the factors that affect polymer production, such as carbon substrates, catalyst structure, and electron transport proteins, demonstrate the tunable nature of the reaction and suggest that bacterial metabolism can be coupled to redox-active metal catalysts to drive chemical reactions beyond polymerization. — P.G.
Computational analysis of putative hominin burials
Partial baboon skeleton from Misgrot Cave, South Africa, used for comparative analysis.
Fossil remains of hominins found in the caves of Spain’s Sima de los Huesos and South Africa’s Dinaledi Chamber are purported to bear evidence suggesting mortuary practices among Middle Pleistocene hominins. Such practices would imply cultural awareness of human mortality and ritual reverence among hominins. Charles Egeland et al. (pp. 4601–4606) used a machine learning approach to compare the abundance of hominin skeletal parts in both fossil assemblages with 14 modern and prehistoric sets of remains sorted into distinct categories. The categories included primary hominin burial, possible primary hominin burial, hominin nonanthropogenically accumulated fossils, undisturbed human corpses, and scavenged human corpses, among others. Analysis of skeletal part abundance suggested that the Spanish fossils were unlikely to have been deposited as complete skeletons and that they were likely disturbed by carnivores, which may have fed on the bones and inflicted surface damage. Similarly, the South African hominin remains were unlikely to have arrived at the caves as complete skeletons and revealed signs of subsequent disturbance. Comparative analyses suggested that abiotic factors and carnivores may have contributed to the composition and disarray observed in the assemblages. Contrary to previous suggestions, neither fossil collection offers unambiguous evidence of burial by hominins. Yet the findings do not rule out the possibility that such burials occurred; instead, they underscore a potential role for nonhuman agents and the need for further scrutiny, according to the authors. — P.N.