OsPP65 Negatively Regulates Osmotic and Salt Stress Responses Through Regulating Phytohormone and Raffinose Family Oligosaccharide Metabolic Pathways in Rice

Although type 2C protein phosphatases (PP2Cs) have been demonstrated to play important roles in regulating plant development and various stress responses, their specific roles in rice abiotic stress tolerance are still largely unknown. In this study, the functions of OsPP65 in rice osmotic and salt stress tolerance were investigated. Here, we report that OsPP65 is responsive to multiple stresses and is remarkably induced by osmotic and salt stress treatments. OsPP65 was highly expressed in rice seedlings and leaves and localized in the nucleus and cytoplasm. OsPP65 knockout rice plants showed enhanced tolerance to osmotic and salt stresses. Significantly higher induction of genes involved in jasmonic acid (JA) and abscisic acid (ABA) biosynthesis or signaling, as well as higher contents of endogenous JA and ABA, were observed in the OsPP65 knockout plants compared with the wild-type plants after osmotic stress treatment. Further analysis indicated that JA and ABA function independently in osmotic stress tolerance conferred by loss of OsPP65 . Moreover, metabolomics analysis revealed higher endogenous levels of galactose and galactinol but a lower content of raffinose in the OsPP65 knockout plants than in the wild-type plants after osmotic stress treatment. These results together suggest that OsPP65 negatively regulates osmotic and salt stress tolerance through regulation of the JA and ABA signaling pathways and modulation of the raffinose family oligosaccharide metabolism pathway in rice. OsPP65 is a promising target for improvement of rice stress tolerance using gene editing.