Protein tyrosine phosphatase IBR5 positively affects salt stress response by modulating CAT2 activity

Salt stress induces overproduction of reactive oxygen species (ROS), disrupting cellular redox homeostasis and impairing plant growth. As a key ROS-scavenging enzyme, catalase (CAT) is pivotal in maintaining ROS homeostasis. While CAT activity is known to be regulated by multiple protein kinases, the involvement of protein phosphatases in this process remains less understood. Here, we report that Arabidopsis thaliana mutants of Indole-3-Butyric Acid Response 5 (IBR5), a member of protein tyrosine phosphatase family, exhibit increased sensitivity to salt stress and elevated ROS level under saline conditions. Transcriptomic profiling revealed differential expression of salt and ROS responsive genes in the ibr5 mutant. Moreover, IBR5 directly interacted with CAT1, CAT2, and CAT3, and salt treatment enhanced the association between IBR5 and CAT2. IBR5 dephosphorylated CAT2 in vitro, while the phosphorylation level of CAT2 increased in ibr5 mutant. Moreover, the catalase activity decreased in ibr5 mutant, and overexpression of CAT2 partially rescued the salt-hypersensitive phenotype of the ibr5 mutant. These findings establish that IBR5 regulates ROS homeostasis under salt stress by modulating the phosphorylation status of CAT2 in Arabidopsis.