Rice small protein OsS1Fa1 participates in stress responses as an inner nuclear membrane protein.

The rice small protein OsS1Fa1, a homolog of spinach S1Fa, plays a significant role in drought tolerance, attributed to its transmembrane domain. In this study, we aim to further elucidate the potential roles of OsS1Fa1 in cold and biotic stresses as an inner nuclear membrane protein. Fluorescence analysis confirmed the localization of OsS1Fa1 to the inner nuclear membrane. Utilizing the bimolecular fluorescence complementation (BiFC) and bacterial infiltration assays with OsS1Fa1 and the inner nuclear membrane protein OsSUN1 (Rice Sad1 and UNC84 (SUN) domain containing 1 (SUN1)), we observed fluorescence detection within the inner nuclear membrane, indicating a direct interaction and colocalization between OsS1Fa1 and OsSUN1. Expression analysis revealed that overexpression of OsS1Fa1 induced the expression of various genes associated with cold and defense responses, including COLD-REGULATED 15A (COR15A), PATHOGENESIS-RELATED PROTEIN 1 (PR1), and PLANT DEFENSIN 1.2 (PDF1.2). Our findings collectively indicate that OsS1Fa1 plays crucial roles in both abiotic and biotic stress tolerance as an inner nuclear membrane protein.