Two-component systems (TCSs) have been identified as participants in mediating plant response to water deficit. Nevertheless, insights of their contribution to plant drought responses and associated regulatory mechanisms remain limited. Herein, a soybean response regulator (RR) gene RR34, which is the potential drought-responsive downstream member of a TCS, was ectopically expressed in the model plant Arabidopsis for the analysis of its biological roles in drought stress response. Results from the survival test revealed outstanding recovery ratios of 52%–53% in the examined transgenic lines compared with 28% of the wild-type plants. Additionally, remarkedly lower water loss rates in detached leaves as well as enhanced antioxidant enzyme activities of catalase and superoxide dismutase were observed in the transgenic group. Further transcriptional analysis of a subset of drought-responsive genes demonstrated higher expression in GmRR34-transgenic plants upon exposure to drought, including abscisic acid (ABA)-related genes NCED3, OST1, ABI5, and RAB18. These ectopic expression lines also displayed hypersensitivity to ABA treatment at germination and post-germination stages. Collectively, these findings indicated the ABA-associated mode of action of GmRR34 in conferring better plant performance under the adverse drought conditions.
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Plants, as sessile organisms, are susceptible to a myriad of stress factors, especially abiotic stresses. Over the course of evolution, they have developed multiple mechanisms to sense and transduce environmental stimuli for appropriate responses. Among those, phosphorylation and dephosphorylation, regulated by protein kinases and protein phosphatases, respectively, are considered as crucial signal transduction mechanisms. Regarding the latter group, protein phosphatases type 2C (PP2Cs) represent the largest division of PPs. In addition, discovery of regulatory functions of PP2Cs in abscisic acid (ABA)-signaling pathway, the major signal transduction pathway in abiotic stress responses, indicates significant importance of PP2C members in plant adaptation to adverse environmental factors. In this review, current understanding of the roles of PP2Cs in different phytohormone-dependent pathways related to abiotic stress is summarized, highlighting the crosstalk between the ABA-signaling pathway with other hormonal pathways via certain ABA-related PP2Cs. We also updated progress of in planta characterization studies of PP2Cs under abiotic stress conditions, providing knowledge of PP2C manipulation in developing abiotic stress-tolerant crops.
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