BSMT1, SABP3, and MAT2 assemble into a ternary complex vital for methyl salicylate biosynthesis and airborne defense

When plants encounter biotic and abiotic stresses, they emit various volatile organic compounds to communicate with nearby plants and activate airborne defense (AD). One critical compound in this process is methyl salicylate (MeSA). Previous studies have mostly examined how stress triggers the production of MeSA at the gene level. In our study, we found that MeSA plays a key role in AD during bacterial infections and determined how plants boost MeSA production through a protein complex. Infection by Pseudomonas syringae pv. tomato DC3000 in Arabidopsis thaliana increased salicylic acid levels, leading to the formation of a ternary protein complex in the cytoplasm. This complex consists of benzoic acid/salicylic acid carboxyl methyltransferases (BSMT1), salicylic acid-binding protein 3 (SABP3), and S-adenosyl methionine synthetase 2 (MAT2). Together, they enhance MAT2's ability to produce S-adenosyl methionine (SAM), a precursor to MeSA, and boost BSMT1's capacity to synthesize MeSA. The produced MeSA then triggers AD in nearby plants and initiates systemic acquired resistance in the infected plant. Our findings clarify the MeSA production pathway during pathogen attacks and show that MeSA-mediated AD is a common defense against both insect and pathogen threats, emphasizing its potential as a potent plant immune inducer.