Spatial distribution of the lectin protein Osr40g3 determines its dual regulatory function in imparting salinity tolerance while impeding seed development in rice
Under changing environmental conditions, salt stress has posed a severe threat to agriculture. Although the R40 family lectins are known to be associated with osmotic stress response, their mechanism of action remains elusive. Among them, Osr40g3 displays the highest expression under salt stress. Here, we report that the constitutive overexpression of Osr40g3 imparts salt tolerance but displays pollen sterility and poor seed development in rice. Promoter analysis and gene expression studies revealed that the gene follows a precise tissue-specific expression pattern, which is essential for proper seed development. Overexpressing the gene under the control of its native promoter rescued the pollen-sterile phenotype while significantly improving salt tolerance. Protein-protein interaction studies demonstrated that Osr40g3 positively regulates an expansin protein, OsEG45, while decreasing the stability of a 14-3-3 protein, OsGF14e. Correspondingly, the OsEG45 overexpression and OsGF14e silencing lines display a salt-tolerant phenotype. Again, silencing OsEG45 in the background of OsGF14e silencing lines resulted in a salt-sensitive phenotype, indicating that salt tolerance of the OsGF14e silencing lines is OsEG45-dependent. Notably, the OsGF14e gene displays early salt responsiveness, while Osr40g3 and OsEG45 display a late response, indicating a spatio-temporal regulation of these genes. Interestingly, constitutive overexpression of Osr40g3 or silencing of OsGF14e leads to diminished gibberellic acid (GA) accumulation that activates the OsEG45 gene. Together, our study demonstrates that during salt stress, Osr40g3, a late salt-responsive gene, confers salt tolerance by negatively regulating OsGF14e while positively regulating OsEG45 via a GA-mediated pathway. This mechanistic insight broadens our understanding of lectin-mediated regulation of salt tolerance.