Wall-associated kinase-like4 regulates plant salt tolerance by maintaining cell wall pectin homeostasis and cellular redox homeostasis in Arabidopsis.

Soil salinization poses a significant threat to global agricultural productivity. Understanding the molecular mechanisms that enable plants to cope with salt stress is crucial for developing salt-resilient crops. We found that several Arabidopsis WAK/WAKL genes are upregulated by salt stress, and their loss-of-function mutants exhibit altered salt tolerance compared WT plants. Here, we focused on WAKL4 and demonstrated that it plays a pivotal positive regulatory role in salt tolerance in Arabidopsis thaliana (Arabidopsis). Loss of WAKL4 function resulted in enhanced sensitivity to salt stress, while WAKL4 overexpression conferred enhanced root growth and reduced germination. In addition, WAKL4 only has minor effect on ionic homeostasis regulation during salt response. Importantly, we found that WAKL4 functions in maintaining cell wall integrity under salt stress, primarily through ensuring the normal biosynthesis of pectin. The salt-sensitive phenotype of the wakl4 mutant was associated with deficiency in pectin content and could be effectively rescued by exogenous calcium supplementation. Furthermore, we discovered that WAKL4 is essential for redox homeostasis regulation during salt response. The wakl4 mutant accumulated excessive reactive oxygen species (ROS) compared to WT plants. Interestingly, the expression levels of some ROS-related genes in the wakl4 mutant was also lower than that in WT plants under salt stress. WAKL4 directly interacts with and enhances the enzymatic activity of CATALASE2 (CAT2), a central enzyme in H₂O₂ scavenging. WAKL4 regulates plant salt tolerance partly via the action of CAT2. This study provides insights into plant salt tolerance and offers possible genetic targets for the improvement of crop tolerance in saline soils.