Regulation of Common Early and Late Stress Responses in Rice by Transcriptional and Antioxidant Mechanisms Under Salt Stress

Salinity is one of the limiting factors that reduce crop production and yield. The salinity tolerance response of plants varies depending on the growth stages. Although the previous studies showed salinity tolerance responses of plants at early or late stages, the common early and late salinity tolerance response of rice plants has yet to be discovered. We investigated the common early (6-h salt exposure) and late (30-days salt exposure) physiological, biochemical, and transcriptome responses associated with salinity tolerance in salt-tolerant (ST) and sensitive (SS) rice genotypes with almost 99% identical genomes. The physiological salinity response of ST and SS genotypes appeared at the late stage. However, early and late biochemical responses of ST and SS genotypes to salt stress were observed in similar patterns. In the common early and late salt stress response, several transcription factors, such as OsbHLH120, OsbZIP61, OsYAB1, OsBBX19, and OsMYB19, and abiotic stress-related genes like OsVQ30, OsGELP4, OsRADC1, and OsPMEI28 upregulated in the ST genotype. The ST genotype improved salt tolerance in several ways. In particular, lowered Na+ accumulation, H2O2, and MDA content and improved photosynthetic pigments, photosynthesis rate, K+ accumulation, osmoprotectant proline, and antioxidant enzyme activity (SOD, CAT, APX, GR, and GPX) may relate the common transcriptomic response. These modifications collectively contributed to the improved salinity tolerance observed in the ST genotype at early and late stages. These findings will contribute to understanding early and late salinity tolerance response mechanisms in rice.