Dual Repression by IPA1 Fine-Tunes OsbZIP79-Mediated Salt Tolerance in Rice

Soil salinity severely impairs rice yield and quality, yet the molecular mechanisms of its salt tolerance remain unclear. In this study, we first discovered OsbZIP79, a novel basic leucine zipper (bZIP)-type transcription factor, as a positive regulator of salt tolerance in rice. We uncovered that OsbZIP79 positively regulates the expression of OsHAK26 (encoding a potassium transporter) and OsMPG1 (encoding a mannose-1-phosphate guanylyltransferase) to confer salt tolerance in rice. In vivo and in vitro evidence demonstrate that OsbZIP79 physically interacts with Ideal Plant Architecture1 (IPA1), a known negative regulator of salt stress responses. IPA1 represses the expression of OsbZIP79 and competes with the OsbZIP79 C-terminus for binding to the promoters of its target genes. Haplotype analysis of 4726 rice accessions identified Hap3 of OsbZIP79 as a favorable allele that confers significantly enhanced salinity tolerance compared to Hap1 and Hap2. These findings reveal a novel salt tolerance regulatory network governed by the OsbZIP79-IPA1 module. This work provides insights to facilitate the improvement of salt tolerance in rice through advanced breeding.