Hydrolysis of indole glucosinolates by PENETRATION2 modulates camalexin production and resistance to Botrytis cinerea in Arabidopsis thaliana.

Plants produce a wide array of antimicrobial compounds to defend against pathogens and pests. In Brassicaceae, aliphatic and indole glucosinolates (AGS and IGS), derived from methionine and tryptophan, are converted, in response to infection or wounding, by myrosinases into isothiocyanates, nitriles, and other compounds with antimicrobial activity. In Arabidopsis thaliana, PENETRATION2 (PEN2) specifically hydrolyze IGS, contributing to resistance against different fungal pathogens. IGS share part of their biosynthetic pathway with the indole phytoalexin camalexin, but the regulation of their production and their relative contribution to defense are not fully elucidated. We found that pen2 mutants show increased camalexin production and reduced symptoms when infected with the fungal pathogen Botrytis cinerea. This resistance is lost when pen2 is crossed with the pad3 mutant, defective in camalexin biosynthesis. Additionally, pen2-mediated resistance is also lost in a cyp79f2 mutant background, defective in the biosynthesis of 4MI3G, a direct substrate of PEN2. These results suggest that the accumulation of non-hydrolyzed 4MI3G leads to enhanced camalexin production and increased resistance. These results highlight that feedback mechanisms fine-tune the accumulation of antimicrobial metabolites during pathogen infection.