From isochorismate to salicylate: a new reaction mechanism for salicylic acid biosynthesis

Abstract

Abstract Salicylic acid (SA) is an essential regulator of plant immune responses. Despite decades of research, our knowledge of its biosynthesis remains incomplete. Here we report that by conjugating glutamate to isochorismic acid, avrPphB Susceptible 3 (PBS3) catalyzes the formation of Isochorismate-9-glutamate (ISC-9-Glu), which then further decays into SA without the requirement of any enzymatic catalysis. Thus, plant SA biosynthesis can be reconstituted with just the two enzymes Isochorismate Synthase 1 (ICS1) and PBS3, along with the putative isochorismate transporter Enhanced Disease Susceptibility 5 (EDS5). This is the very first example of a decay-driven biosynthesis of a phytohormone. One Sentence Summary PBS3 produces SA via Isochorismate-9-glutamate.