Salt stress can significantly affect plant growth and agricultural productivity. Receptor-like kinases (RLKs) are believed to play essential roles in plant growth, development and responses to abiotic stresses. Here, we identify a receptor-like cytoplasmic kinase, salt tolerance receptor-like cytoplasmic kinase 1 (STRK1), from rice (Oryza sativa L.) that positively regulates salt and oxidative stress tolerance. Our results show that STRK1 anchors and interacts with CatC at the plasma membrane via palmitoylation. CatC is phosphorylated mainly at Tyr210 and activated by STRK1. The phosphorylation mimic form CatCY210D exhibits higher catalase activity both in vitro and in planta, and salt stress enhances STRK1-mediated tyrosine phosphorylation on CatC. Compared with wild-type plants, STRK1-overexpressing plants exhibited higher catalase activity and lower accumulation of H2O2 as well as higher tolerance to salt and oxidative stress. Our findings demonstrate that STRK1 improves salt and oxidative tolerance by phosphorylating and activating CatC and thereby regulating H2O2 homeostasis. Moreover, overexpression of STRK1 in rice not only improved growth at the seedling stage but also markedly limited the grain yield loss under salt stress conditions. Together, these results offer an opportunity to improve rice grain yield under salt stress.

Significance: Receptor-like kinase FERONIA (FER) is a versatile regulator of cell growth under both normal and stress environments. FER binds its peptide ligand, rapid alkalinization factor 1 (RALF1), and triggers downstream events to inhibit cell growth in primary roots. However, the mechanism of RALF1 reception by FER is still largely unknown. In this study, we identified a receptor-like cytoplasmic kinase (RPM1-induced protein kinase, RIPK) that directly interacts with and is phosphorylated by FER in a RALF1 peptide-dependent manner. The defects of fer-4 mutant in RALF1 response and root hair development are mimicked by ripk loss-of-function but partially compensated by RIPK overexpression. These and other data suggest that formation of the FER–RIPK complex serves as a crucial step in the RALF1 signaling pathway.