Mutual Promotion of LAP2 and CAT2 Synergistically Regulates Plant Salt and Osmotic Stress Tolerance

Abstract

Almost all abiotic stresses induce reactive oxygen species (ROS) overaccumulation, causing oxidative damages to plant cells. Catalase (CAT) plays a vital role in plant oxidative stress tolerance by scavenging stress-induced excess H₂O₂; thus, the identification of factors regulating catalase function will shed light on the underlying regulatory mechanisms. Here, we identified leucine aminopeptidase 2 (<i>LAP2</i>) as a novel <i>CAT2</i>-interacting protein and showed a mutual promotion effect of the two proteins in plant stress responses. <i>LAP2</i> has a physical interaction with <i>CAT2</i> in plant cells. The loss-of-function mutant of <i>LAP2</i>, <i>lap2-3</i>, is hypersensitive to salt or osmotic stress with increased ROS accumulation and malondialdehyde content and decreased catalase activity. The <i>lap2-3</i> mutant has less <i>CAT2</i> protein levels as <i>CAT2</i> protein stability is impaired in the mutant. Scavenging excess ROS by glutathione or overexpressing <i>CAT2</i> in the <i>lap2-3</i> mutant recovers its hypersensitive phenotype to salt or osmotic stress. Further study showed that <i>CAT2</i> promotes <i>LAP2</i> hydrolysis activity with leucine-4-methylcoumaryl-7-amides as a substrate <i>in vivo</i> and <i>in vitro</i>, and thus, similar to the <i>lap2-3</i> mutant, the <i>cat2-1</i> mutant also has lower γ-aminobutyric acid content than the wild type. Together, our study reveals mutual promotion effects of <i>CAT2</i> and <i>LAP2</i> in conferring plant salt and osmotic stress tolerance.