OsRR26, a type-B response regulator, modulates salinity tolerance in rice via phytohormone-mediated ROS accumulation in roots and influencing reproductive development.

MAIN CONCLUSION: OsRR26 is a cytokinin-responsive response regulator that promotes phytohormone-mediated ROS accumulation in rice roots, regulates seedling growth, spikelet fertility, awn development, represses NADPH oxidases, and negatively affects salinity tolerance. Plant two-component systems (TCS) play a pivotal role in phytohormone signaling, stress responses, and circadian rhythm. However, a significant knowledge gap exists regarding TCS in rice. In this study, we utilized a functional genomics approach to elucidate the role of OsRR26, a type-B response regulator in rice. Our results demonstrate that OsRR26 is responsive to cytokinin, ABA, and salinity stress, serving as the ortholog of Arabidopsis ARR11. OsRR26 primarily localizes to the nucleus and plays a crucial role in seedling growth, spikelet fertility, and the suppression of awn development. Exogenous application of cytokinin led to distinct patterns of reactive oxygen species (ROS) accumulation in the roots of both WT and transgenic plants (OsRR26OE and OsRR26KD), indicating the potential involvement of OsRR26 in cytokinin-mediated ROS signaling in roots. The application of exogenous ABA resulted in varied cellular compartmentalization of ROS between the WT and transgenic lines. Stress tolerance assays of these plants revealed that OsRR26 functions as a negative regulator of salinity stress tolerance across different developmental stages in rice. Physiological and biochemical analyses unveiled that the knockdown of OsRR26 enhances salinity tolerance, characterized by improved chlorophyll retention and the accumulation of soluble sugars, K+ content, and amino acids, particularly proline.

OsCyp2-P, an auxin-responsive cyclophilin, regulates Ca2+ calmodulin interaction for an ion-mediated stress response in rice.

OsCYP2-P is an active cyclophilin (having peptidyl-prolyl cis/trans-isomerase activity, PPIase) isolated from the wild rice Pokkali having a natural capacity to grow and yield seeds in coastal saline regions of India. Transcript abundance analysis in rice seedlings showed the gene is inducible by multiple stresses, including salinity, drought, high temperature, and heavy metals. To dissect the role of OsCYP2-P gene in stress response, we raised overexpression (OE) and knockdown (KD) transgenic rice plants with >2-3 folds higher and approximately 2-fold lower PPIase activity, respectively. Plants overexpressing this gene had more favorable physiological and biochemical parameters (K+ /Na+ ratio, electrolytic leakage, membrane damage, antioxidant enzymes) than wild type, and the reverse was observed in plants that were knocked down for this gene. We propose that OsCYP2-P contributes to stress tolerance via maintenance of ion homeostasis and thus prevents toxic cellular ion buildup and membrane damage. OE plants were found to have a higher harvest index and higher number of filled grains under salinity and drought stress than wild type. OsCYP2-P interacts with calmodulin, indicating it functions via the Ca-CaM pathway. Compared to the WT, the germinating OE seeds exhibited a substantially higher auxin level, and this hormone was below the detection limits in the WT and KD lines. These observations strongly indicate that OsCyp2-P affects the signaling and transport of auxin in rice.

Rewilding staple crops for the lost halophytism: Toward sustainability and profitability of agricultural production systems.

Abiotic stress tolerance has been weakened during the domestication of all major staple crops. Soil salinity is a major environmental constraint that impacts over half of the world population; however, given the increasing reliance on irrigation and the lack of available freshwater, agriculture in the 21st century will increasingly become saline. Therefore, global food security is critically dependent on the ability of plant breeders to create high-yielding staple crop varieties that will incorporate salinity tolerance traits and account for future climate scenarios. Previously, we have argued that the current agricultural practices and reliance on crops that exclude salt from uptake is counterproductive and environmentally unsustainable, and thus called for a need for a major shift in a breeding paradigm to incorporate some halophytic traits that were present in wild relatives but were lost in modern crops during domestication. In this review, we provide a comprehensive physiological and molecular analysis of the key traits conferring crop halophytism, such as vacuolar Na+ sequestration, ROS desensitization, succulence, metabolic photosynthetic switch, and salt deposition in trichomes, and discuss the strategies for incorporating them into elite germplasm, to address a pressing issue of boosting plant salinity tolerance.

Drought and High Temperature Stress in Sorghum: Physiological, Genetic, and Molecular Insights and Breeding Approaches.

Sorghum is one of the staple crops for millions of people in Sub-Saharan Africa (SSA) and South Asia (SA). The future climate in these sorghum production regions is likely to have unexpected short or long episodes of drought and/or high temperature (HT), which can cause significant yield losses. Therefore, to achieve food and nutritional security, drought and HT stress tolerance ability in sorghum must be genetically improved. Drought tolerance mechanism, stay green, and grain yield under stress has been widely studied. However, novel traits associated with drought (restricted transpiration and root architecture) need to be explored and utilized in breeding. In sorghum, knowledge on the traits associated with HT tolerance is limited. Heat shock transcription factors, dehydrins, and genes associated with hormones such as auxin, ethylene, and abscisic acid and compatible solutes are involved in drought stress modulation. In contrast, our understanding of HT tolerance at the omic level is limited and needs attention. Breeding programs have exploited limited traits with narrow genetic and genomic resources to develop drought or heat tolerant lines. Reproductive stages of sorghum are relatively more sensitive to stress compared to vegetative stages. Therefore, breeding should incorporate appropriate pre-flowering and post-flowering tolerance in a broad genetic base population and in heterotic hybrid breeding pipelines. Currently, more than 240 QTLs are reported for drought tolerance-associated traits in sorghum prospecting discovery of trait markers. Identifying traits and better understanding of physiological and genetic mechanisms and quantification of genetic variability for these traits may enhance HT tolerance. Drought and HT tolerance can be improved by better understanding mechanisms associated with tolerance and screening large germplasm collections to identify tolerant lines and incorporation of those traits into elite breeding lines. Systems approaches help in identifying the best donors of tolerance to be incorporated in the SSA and SA sorghum breeding programs. Integrated breeding with use of high-throughput precision phenomics and genomics can deliver a range of drought and HT tolerant genotypes that can improve yield and resilience of sorghum under drought and HT stresses.

Membrane dynamics during individual and combined abiotic stresses in plants and tools to study the same.

The plasma membrane (PM) is possibly the most diverse biological membrane of plant cells; it separates and guards the cell against its external environment. It has an extremely complex structure comprising a mosaic of lipids and proteins. The PM lipids are responsible for maintaining fluidity, permeability and integrity of the membrane and also influence the functioning of membrane proteins. However, the PM is the primary target of environmental stress, which affects its composition, conformation and properties, thereby disturbing the cellular homeostasis. Maintenance of integrity and fluidity of the PM is a prerequisite for ensuring the survival of plants during adverse environmental conditions. The ability of plants to remodel membrane lipid and protein composition plays a crucial role in adaptation towards varying abiotic environmental cues, including high or low temperature, drought, salinity and heavy metals stress. The dynamic changes in lipid composition affect the functioning of membrane transporters and ultimately regulate the physical properties of the membrane. Plant membrane-transport systems play a significant role in stress adaptation by cooperating with the membrane lipidome to maintain the membrane integrity under stressful conditions. The present review provides a holistic view of stress responses and adaptations in plants, especially the changes in the lipidome and proteome of PM under individual or combined abiotic stresses, which cause alterations in the activity of membrane transporters and modifies the fluidity of the PM. The tools to study the varying lipidome and proteome of the PM are also discussed.