OsbZIP35 Mediates ABA-Dependent Drought Tolerance and Stress-Responsive Yield Maintenance in Rice

Rice bZIP transcription factors mediate abiotic stress responses, but OsbZIP35’s function remains unclear. Here, we investigated its role in drought stress and yield regulation. In this study, drought, H2O2, abscisic acid, and NaCl treatments strongly induced the expression of OsbZIP35, whereas treatment with gibberellin, indoleacetic acid, and jasmonic acid did not affect OsbZIP35 expression. Using knockout mutants (bzip35) and overexpression lines (OsbZIP35-OX) for reciprocal validation, we found bzip35 mutants are drought-sensitive, while OsbZIP35-OX lines show enhanced tolerance across during the germination, post-germination growth, and seedling stages. Specifically, the bzip35 mutants exhibited a lower germination percentage, a weaker growth phenotype, and an increase in reactive oxygen species accumulation. Further analysis indicated that, under drought stress, OsbZIP35 regulated reactive oxygen species accumulation by modulating the contents of antioxidants, thereby positively regulating the response of rice seedlings to drought stress. In addition, we observed that OsbZIP35 could be phosphorylated by OsSAPK3 and participated in the abscisic acid signaling pathway in response to drought stress. Agronomic trait analysis revealed that, under drought stress at the heading stage, the panicle length and seed-set rate of bzip35 mutants were significantly lower than those of the wild type. This study examined the role of OsbZIP35 in rice stress tolerance and yield regulation, and identified an upstream regulatory gene, OsSAPK3.