Short-term responses of soybean roots to individual and combinatorial effects of elevated [CO2] and water deficit

Elevated CO2 increases biomass of Sorghum bicolor green prop roots under drought conditions via soluble sugar accumulation and photosynthetic activity

Elevated [CO2 ] (E[CO2 ]) mitigates agricultural losses of C4 plants under drought. Although several studies have described the molecular responses of the C4 plant species Sorghum bicolor during drought exposure, few have reported the combined effects of drought and E[CO2 ] (E[CO2 ]/D) on the roots. A previous study showed that, among plant organs, green prop roots (GPRs) under E[CO2 ]/D presented the second highest increase in biomass after leaves compared with ambient [CO2 ]/D. GPRs are photosynthetically active and sensitive to drought. To understand which mechanisms are involved in the increase in biomass of GPRs, we performed transcriptome analyses of GPRs under E[CO2 ]/D. Whole-transcriptome analysis revealed several pathways altered under E[CO2 ]/D, among which photosynthesis was strongly affected. We also used previous metabolome data to support our transcriptome data. Activities associated with photosynthesis and central metabolism increased, as seen by the upregulation of photosynthesis-related genes, a rise in glucose and polyol contents, and increased contents of chlorophyll a and carotenoids. Protein-protein interaction networks revealed that proliferation, biogenesis, and homeostasis categories were enriched and contained mainly upregulated genes. The findings suggest that the previously reported increase in GPR biomass of plants grown under E[CO2 ]/D is mainly attributed to glucose and polyol accumulation, as well as photosynthesis activity and carbon provided by respiratory CO2 refixation. Our findings reveal that an intriguing and complex metabolic process occurs in GPRs under E[CO2 ]/D, showing the crucial role of these organs in plant drought /tolerance.

A gene regulatory network in Arabidopsis roots reveals features and regulators of the plant response to elevated CO2

The elevation of CO₂ in the atmosphere increases plant biomass but decreases their mineral content. The genetic and molecular bases of these effects remain mostly unknown, in particular in the root system, which is responsible for plant nutrient uptake. To gain knowledge about the effect of elevated CO₂ on plant growth and physiology, and to identify its regulatory in the roots, we analyzed genome expression in Arabidopsis roots through a combinatorial design with contrasted levels of CO₂ , nitrate, and iron. We demonstrated that elevated CO₂ has a modest effect on root genome expression under nutrient sufficiency, but by contrast leads to massive expression changes under nitrate or iron deficiencies. We demonstrated that elevated CO₂ negatively targets nitrate and iron starvation modules at the transcriptional level, associated with a reduction in high-affinity nitrate uptake. Finally, we inferred a gene regulatory network governing the root response to elevated CO₂ . This network allowed us to identify candidate transcription factors including MYB15, WOX11, and EDF3 which we experimentally validated for their role in the stimulation of growth by elevated CO₂ . Our approach identified key features and regulators of the plant response to elevated CO₂ , with the objective of developing crops resilient to climate change.

The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal

The elevation of atmospheric CO₂ concentration has a strong impact on the physiology of C3 plants, far beyond photosynthesis and C metabolism. In particular, it reduces the concentrations of most mineral nutrients in plant tissues, posing major threats on crop quality, nutrient cycles, and carbon sinks in terrestrial agro-ecosystems. The causes of the detrimental effect of high CO₂ levels on plant mineral status are not understood. We provide an update on the main hypotheses and review the increasing evidence that, for nitrogen, this detrimental effect is associated with direct inhibition of key mechanisms of nitrogen uptake and assimilation. We also mention promising strategies for identifying genotypes that will maintain robust nutrient status in a future high-CO₂ world.

Elevated CO2 and Water Stress in Combination in Plants: Brothers in Arms or Partners in Crime?

The changing dynamics in the climate are the primary and important determinants of agriculture productivity. The effects of this changing climate on overall productivity in agriculture can be understood when we study the effects of individual components contributing to the changing climate on plants and crops. Elevated CO₂ (eCO₂) and drought due to high variability in rainfall is one of the important manifestations of the changing climate. There is a considerable amount of literature that addresses climate effects on plant systems from molecules to ecosystems. Of particular interest is the effect of increased CO₂ on plants in relation to drought and water stress. As it is known that one of the consistent effects of increased CO₂ in the atmosphere is increased photosynthesis, especially in C₃ plants, it will be interesting to know the effect of drought in relation to elevated CO₂. The potential of elevated CO₂ ameliorating the effects of water deficit stress is evident from literature, which suggests that these two agents are brothers in arms protecting the plant from stress rather than partners in crime, specifically for water deficit when in isolation. The possible mechanisms by which this occurs will be discussed in this minireview. Interpreting the effects of short-term and long-term exposure of plants to elevated CO₂ in the context of ameliorating the negative impacts of drought will show us the possible ways by which there can be effective adaption to crops in the changing climate scenario.

The Hidden Potential of High-Throughput RNA-Seq Re-Analysis, a Case Study for DHDPS, Key Enzyme of the Aspartate-Derived Lysine Biosynthesis Pathway and Its Role in Abiotic and Biotic Stress Responses in Soybean

DHDPS is a key enzyme in the aspartate-derived lysine biosynthesis pathway and an evident object of study for biofortification strategies in plants. DHDPS isoforms with novel regulatory properties in Medicago truncatula were demonstrated earlier and hypothesized to be involved in abiotic and biotic stress responses. Here, we present a phylogenetic analysis of the DHPDS gene family in land plants which establishes the existence of a legume-specific class of DHDPS, termed DHDPS B-type, distinguishable from the DHDPS A-type commonly present in all land plants. The G. max genome comprises two A-type DHDPS genes (Gm.DHDPS-A1; Glyma.09G268200, Gm.DHDPS-A2; Glyma.18G221700) and one B-type (Gm.DHDPS-B; Glyma.03G022300). To further investigate the expression pattern of the G. max DHDPS isozymes in different plant tissues and under various stress conditions, 461 RNA-seq experiments were exploited and re-analyzed covering two expression atlases, 13 abiotic and 5 biotic stress studies. Gm.DHDPS-B is seen almost exclusively expressed in roots and nodules in addition to old cotyledons or senescent leaves while both DHDPS A-types are expressed constitutively in all tissues analyzed with the highest expression in mature seeds. Furthermore, Gm.DHDPS-B expression is significantly upregulated in some but not all stress responses including salt stress, flooding, ethylene or infection with Phytophthora sojae and coincides with downregulation of DHDPS A-types. In conclusion, we demonstrate the potential of an in-depth RNA-seq re-analysis for the guidance of future experiments and to expand on current knowledge.

Genotypic variation in the response of soybean to elevated CO2

The impact of elevated CO₂ (eCO₂) on soybean productivity is essential to the global food supply because it is the world's leading source of vegetable proteins. This study aimed to understand the yield responses and nutritional impact under free-air CO₂ enrichment (FACE) conditions of soybean genotypes. Here we report that grain yield increased by 46.9% and no reduction in harvest index was observed among soybean genotypes. Elevated CO₂ improved the photosynthetic carbon assimilation rate, leaf area, plant height, and aboveground biomass at vegetative and pod filling stages. Besides the positive effects on yield parameters, eCO₂ differentially affected the overall grain quality. The levels of calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), manganese (Mn), iron (Fe), boron (B), and zinc (Zn) grain minerals decreased by 22.9, 9.0, 4.9, 10.1, 21.3, 28.1, 18.5, and 25.9% under eCO₂ conditions, respectively. Soluble sugars and starch increased by 9.1 and 16.0%, respectively, phytic acid accumulation increased by 8.1%, but grain protein content significantly decreased by 5.6% across soybean genotypes. Furthermore, the antioxidant activity decreased by 36.9%, but the total phenolic content was not affected by eCO₂ conditions. Genotypes, such as Winsconsin Black, Primorskaja, and L-117, were considered the most responsive to eCO₂ in terms of yield enhancement and less affected in the nutritional quality. Our results confirm the existence of genetic variability in soybean responses to eCO₂, and differences between genotypes in yield improvement and decreased sensitivity to eCO₂ in terms of grain quality loss could be included in future soybean selection to enable adaptation to climate change.

Short Term Elevated CO2 Interacts with Iron Deficiency, Further Repressing Growth, Photosynthesis and Mineral Accumulation in Soybean (Glycine max L.) and Common Bean (Phaseolus vulgaris L.)

Elevated CO2 (eCO2) has been reported to cause mineral losses in several important food crops such as soybean (Glycine max L.) and common bean (Phaseolus vulgaris L.). In addition, more than 30% of the world’s arable land is calcareous, leading to iron (Fe) deficiency chlorosis and lower Fe levels in plant tissues. We hypothesize that there will be combinatorial effects of eCO2 and Fe deficiency on the mineral dynamics of these crops at a morphological, biochemical and physiological level. To test this hypothesis, plants were grown hydroponically under Fe sufficiency (20 μM Fe-EDDHA) or deficiency (0 μM Fe-EDDHA) at ambient CO2 (aCO2, 400 ppm) or eCO2 (800 ppm). Plants of both species exposed to eCO2 and Fe deficiency showed the lowest biomass accumulation and the lowest root: shoot ratio. Soybean at eCO2 had significantly higher chlorophyll levels (81%, p < 0.0001) and common bean had significantly higher photosynthetic rates (60%, p < 0.05) but only under Fe sufficiency. In addition, eCO2 increased ferric chelate reductase acivity (FCR) in Fe-sufficient soybean by 4-fold (p < 0.1) and in Fe-deficient common bean plants by 10-fold (p < 0.0001). In common bean, an interactive effect of both environmental factors was observed, resulting in the lowest root Fe levels. The lowering of Fe accumulation in both crops under eCO2 may be linked to the low root citrate accumulation in these plants when grown with unrestricted Fe supply. No changes were observed for malate in soybean, but in common bean, shoot levels were significantly lower under Fe deficiency (77%, p < 0.05) and Fe sufficiency (98%, p < 0.001). These results suggest that the mechanisms involved in reduced Fe accumulation caused by eCO2 and Fe deficiency may not be independent, and an interaction of these factors may lead to further reduced Fe levels.

Effects of elevated CO2 on foliar soluble nutrients and functional components of tea, and population dynamics of tea aphid, Toxoptera aurantii

The rising atmospheric CO₂ concentration has shown to affect plant physiology and chemistry by altering plant primary and secondary metabolisms. Nevertheless, the impacts of elevated CO₂ on plant nutrients and functional components of tea remain largely unknown, which will likely affect tea quality and taste under climate change scenario. Being sources of nutrients and secondary chemicals/metabolites for herbivorous insects, the variation in foliar soluble nutrients and functional components of tea plants resulting from CO₂ enrichment will further affect the herbivorous insects' occurrence and feeding ecology. In this study, the tea aphid, Toxoptera aurantii was selected as the phloem-feeding herbivore to study the effects of elevated CO₂ on foliar soluble nutrients and functional components of tea seedlings, and the population dynamics of T. aurantii. The results indicated that elevated CO₂ enhanced the photosynthetic ability and improved the plant growth of tea seedlings compared with ambient CO₂, with significant increases in net photosynthetic rate (+20%), intercellular CO₂ concentration (+15.74%), leaf biomass (+15.04%) and root-to-shoot ratio (+8.08%), and significant decreases in stomatal conductance (-5.52%) and transpiration rate (-9.40%) of tea seedlings. Moreover, elevated CO₂ significantly increased the foliar content of soluble sugars (+4.74%), theanine (+3.66%) and polyphenols (+12.01%) and reduced the foliar content of free amino acids (-9.09%) and caffeine (-3.38%) of tea seedlings compared with ambient CO₂. Furthermore, the relative transcript levels of the genes of theanine synthetase (+18.64%), phenylalanine ammonia lyase (+49.50%), s'-adenosine methionine synthetase (+143.03%) and chalcone synthase (+61.86%) were up-regulated, and that of caffeine synthase (-56.91%) was down-regulated for the tea seedlings grown under elevated CO₂ relative to ambient CO₂. In addition, the foliar contents of jasmonic acid (+98.6%) and salicylic acid (+155.6%) also increased for the tea seedlings grown under elevated CO₂ in contrast to ambient CO₂. Also, significant increases in the population abundance of T. aurantii (+4.24%-41.17%) were observed when they fed on tea seedlings grown under elevated CO₂ compared to ambient CO₂. It is presumed that the tea quality and taste will be improved owing to the enhanced foliar soluble nutrients and functional components of tea seedlings under the climate change scenario, especially on account of the rising atmospheric CO₂ concentration, while the climate change may exacerbate the occurrence of tea aphid, T. aurantii, despite the enhanced secondary defensive chemicals manifested by the CO₂ enrichment.