Role of KAT2 Oxidation in the Antagonistic Relationship Between Salicilic Acid and Jasmonic Acid in Plant Immnunity

Unlike mammals with adaptive immunity, plants rely on their innate immunity based on pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) for pathogen defense. Reactive oxygen species, known to play crucial roles in PTI and ETI, can perturb cellular redox homeostasis and lead to changes of redox-sensitive proteins through modification of cysteine sulfhydryl groups. Although redox regulation of protein functions has emerged as an important mechanism in several biological processes, little is known about redox proteins and how they function in PTI and ETI. In this study, cysTMT proteomics technology was used to identify similarities and differences of protein redox modifications in tomato resistant (PtoR) and susceptible (prf3) genotypes in response to Pseudomonas syringae pv tomato infection. Interestingly, the protein 3-ketoacyl-CoA thiolase (KAT2) was found to undergo oxidation at late stage of infection in PtoR. KAT2 is one of the three core enzymes that catalyze b-oxidation, which is an important pathway for JA synthesis. At 24 h after pathogen inoculation, SA is expected to play a big role in plant defense. Therefore, oxidation of KAT2 may be the functional switch in the antagonistic interaction between SA and JA.  Arabidopsis thaliana KAT2 is known to be a sensitive redox switch protein, where the oxidized form of the enzyme is inactive and the reduced for is active. Currently, in vitro enzyme activity assays and in vivo phenotypic resistance testing in WT and KAT2 mutant plants have been conducted in order to confirm the role of KAT2 oxidation in plant immunity response.