A Glycine soja methionine sulfoxide reductase B5a interacts with the Ca 2+ / CAM ‐binding kinase Gs CBRLK and activates ROS signaling under carbonate alkaline stress

Although research has extensively illustrated the molecular basis of plant responses to salt and high‐ pH stresses, knowledge on carbonate alkaline stress is poor and the specific responsive mechanism remains elusive. We have previously characterized a Glycine soja Ca 2+ / CAM ‐dependent kinase Gs CBRLK that could increase salt tolerance. Here, we characterize a methionine sulfoxide reductase ( MSR ) B protein Gs MSRB 5a as a Gs CBRLK interactor by using Y2H and BiFc assays. Further analyses showed that the N‐terminal variable domain of Gs CBRLK contributed to the Gs MSRB 5a interaction. Y2H assays also revealed the interaction specificity of Gs CBRLK with the wild soybean MSRB subfamily proteins, and determined that the BoxI/Box II ‐containing regions within Gs MSRB s were responsible for their interaction. Furthermore, we also illustrated that the N‐terminal basic regions in Gs MSRB s functioned as transit peptides, which targeted themselves into chloroplasts and thereby prevented their interaction with Gs CBRLK . Nevertheless, deletion of these regions allowed them to localize on the plasma membrane ( PM ) and interact with Gs CBRLK . In addition, we also showed that Gs MSRB 5a and Gs CBRLK displayed overlapping tissue expression specificity and coincident expression patterns under carbonate alkaline stress. Phenotypic experiments demonstrated that Gs MSRB 5a and Gs CBRLK overexpression in Arabidopsis enhanced carbonate alkaline stress tolerance. Further investigations elucidated that Gs MSRB 5a and Gs CBRLK inhibited reactive oxygen species ( ROS ) accumulation by modifying the expression of ROS signaling, biosynthesis and scavenging genes. Summarily, our results demonstrated that Gs CBRLK and Gs MSRB 5a interacted with each other, and activated ROS signaling under carbonate alkaline stress. Carbonate alkaline stress is a widespread environmental problem that severely restricts crop production. The basic mechanisms used by plants to respond to this stress are less characterized than responses to salt and high‐ pH stresses. Here we use a wild soybean species that is tolerant to carbonate alkaline stress to describe a methionine sulfoxide reductase that interacts with a previously described protein kinase implicated in stress tolerance, to affect ROS signaling.