Osr40g3 Imparts Salt Tolerance by Regulating GF14e-mediated Gibberellin Metabolism to Activate EG45 in Rice.

Under changing environmental conditions, salt stress is a serious threat to agriculture. The R40 family lectins are known to be associated with osmotic stress response, although their mechanism of action remains unclear. Here, we report that Osr40g3, upregulated by salt, improves salt tolerance but causes pollen sterility and poor seed development in rice when constitutively overexpressed. Osr40g3 knockout lines, on the other hand, display salt sensitivity with no other phenotypic aberration. Further studies revealed that the gene exhibits a precise tissue-specific expression pattern essential for seed development. Overexpressing the Osr40g3 with its native promoter alleviates pollen sterility and improves salt tolerance. In-depth molecular studies demonstrated that Osr40g3 positively regulates an expansin protein, OsEG45, while decreasing the stability of a 14-3-3 protein, OsGF14e. Correspondingly, OsEG45 overexpression, OsGF14e silencing lines and the double mutants display salt tolerance, supporting the involvement of the Osr40g3-OsGF14e-OsEG45 module in salt tolerance. Moreover, constitutive overexpression of Osr40g3 or silencing of OsGF14e diminishes gibberellic acid (GA) accumulation that activates the OsEG45 gene. Together, our study highlights that the Osr40g3 confers salt tolerance by negatively regulating OsGF14e while positively regulating OsEG45 via a GA-dependent pathway.