Mechanisms behind idr1-1 mutation conferring osmotic-stress tolerance to rice seedlings as revealed by stage-based...

Osmotic stress, which is mainly caused by water deficiency, is one of the major environmental factors limiting rice productivity. Osmotic stress influences many aspects of plant growth and development, especially flowering. The α subunit of the heterotrimeric G protein complex, IDR1 (also known as RGA1), has been reported to be involved in multiple abiotic-stress responses, while its role in coping with osmotic stress remains unclear. Here, we performed stress stage-based transcriptomic analyses of rice leaves from idr1-1 mutant and wild-type IAPAR9 seedlings that underwent early or middle stage of osmotic stress induced by 20% PEG solution, in order to ascertain the differences in transcriptomes between idr1-1 mutant and IAPAR9 seedlings following early- or middle-stage osmotic stress. Our results showed that 2881 upregulated and 2191 downregulated differentially expressed genes (DEGs) were identified in idr1-1 mutant seedlings relative to wild-type IAPAR9 seedlings under early-stage osmotic stress. Similarly, 2824 upregulated and 2153 downregulated DEGs were also detected in idr1-1 mutant seedlings relative to IAPAR9 seedlings under middle-stage osmotic stress. Overlap analyses revealed that 44 and 325 DEGs were found in idr1-1 mutant seedlings under early and middle stages of osmotic stress, respectively, which were co-regulated by both idr1-1 mutation and osmotic stress. Gene Ontology (GO) analyses of these DEGs demonstrated that in idr1-1 mutant seedlings, GO terms were mainly associated with quick responses to stress (including responses to phytohormones, scavenging of ROS and stomatal movement) following early-stage osmotic stress, while those were associated with operation of photosynthetic systems (including assembly and repair of photosystem complexes, chlorophyll catabolism, and thylakoid) following middle-stage osmotic stress. Interaction assays indicated that IDR1 was able to interact with 5 proteins, OsFLU1, OsHHO3, OsRLIN1, NADPH HC and OsS40-14, with their gene expression being also regulated by idr1-1 mutation. Altogether, our results suggest that idr1-1 mutation contributes to enhanced tolerance to osmotic stress by altering responsiveness to different physiological processes, like responses to water deficit, salt and heat stresses, phytohormone signaling, ROS scavenging, biosynthesis of secondary metabolites, and maintenance and repair of photosynthetic systems, which may play essential roles in enabling idr1-1 mutant seedlings to survive persistent osmotic stress.