The CBL-interacting protein kinase 9 (OsCIPK9) contributes to saline-alkali stress tolerance in rice

Saline-alkali stress significantly affects rice productivity, limiting the plants' ability to absorb nutrients, leading to oxidative stress. Calcium-signaling molecules, including the CBL-CIPK network, serve as stress signals and regulators, tightly controlling reactive oxygen species (ROS) homeostasis. In this study, we conducted transcriptomic and phenotypic analyses, revealing that OsCIPK9 expression is activated by saline-alkali stress, showing early expression in the roots. The qRT-PCR analysis demonstrated that OsCIPK9 is more expressed in the roots during stress responses. Phenotypic assays indicated that Oscipk9 mutants exhibited improved germination rates, longer roots, and higher recovery rates, while overexpression lines displayed significantly delayed germination, shorter roots, increased sensitivity, and lower recovery rates under saline-alkali stress compared to wild-type plants. Furthermore, Oscipk9 mutants maintained higher photosynthetic efficiency and chlorophyll content, whereas overexpression lines showed reduced photosynthetic efficiency and lower chlorophyll content. Additionally, the Oscipk9 mutant exhibited elevated levels of ROS scavenging enzymes, reduced MDA levels, and higher expression of ROS-scavenging genes, while overexpression lines accumulated lower levels of ROS scavenging enzymes and higher MDA levels. Our findings establish that OsCIPK9 contributes saline-alkali response by negatively modulating ROS homeostasis.