OsASR5 enhances drought tolerance through a stomatal closure pathway associated with ABA and H2O2 signalling in rice

Drought is one of the major abiotic stresses that directly implicate plant growth and crop productivity. Although many genes in response to drought stress have been identified, genetic improvement to drought resistance especially in food crops is showing relatively slow progress worldwide. Here, we reported the isolation of abscisic acid, stress and ripening (ASR) genes from upland rice variety, IRAT109 (Oryza sativa L. ssp. japonica), and demonstrated that overexpression of OsASR5 enhanced osmotic tolerance in Escherichia coli and drought tolerance in Arabidopsis and rice by regulating leaf water status under drought stress conditions. Moreover, overexpression of OsASR5 in rice increased endogenous ABA level and showed hypersensitive to exogenous ABA treatment at both germination and postgermination stages. The production of H₂O₂, a second messenger for the induction of stomatal closure in response to ABA, was activated in overexpression plants under drought stress conditions, consequently, increased stomatal closure and decreased stomatal conductance. In contrast, the loss‐of‐function mutant, osasr5, showed sensitivity to drought stress with lower relative water content under drought stress conditions. Further studies demonstrated that OsASR5 functioned as chaperone‐like protein and interacted with stress‐related HSP40 and 2OG‐Fe (II) oxygenase domain containing proteins in yeast and plants. Taken together, we suggest that OsASR5 plays multiple roles in response to drought stress by regulating ABA biosynthesis, promoting stomatal closure, as well as acting as chaperone‐like protein that possibly prevents drought stress‐related proteins from inactivation.     

The jasmonic acid‐signalling and abscisic acid‐signalling pathways cross talk during one,but not repeated,dehydration stress: a non‐specific ‘panicky’ or a meaningful response?

Experiencing diverse and recurring biotic and abiotic stresses throughout life, plants have evolved mechanisms to respond, survive and, eventually, adapt to changing habitats. The initial response to drought involves a large number of genes that are involved also in response to other stresses. According to current models, this initial response is non‐specific, becoming stress‐specific only at later time points. The question, then, is whether non‐specific activation of various stress‐signalling systems leading to the expression of numerous stress‐regulated genes is a false‐alarm (panicky) response or whether it has biologically relevant consequences for the plant. Here, it is argued that the initial activation of genes associated other stresses reflects an important event during which stress‐specific mechanisms are generated to prevent subsequent activation of non‐drought signalling pathways. How plants discriminate between a first and a repeated dehydration stress and how repression of non‐drought specific genes is achieved will be discussed on the example of jasmonic acid‐associated Arabidopsis genes activated by a first, but not subsequent, dehydration stresses. Revealing how expression of various biotic/abiotic stress responding genes is prevented under recurring drought spells may be critical for our understanding of how plants respond to dynamically changing environments.