PBS3 and EPS1 Complete Salicylic Acid Biosynthesis from Isochorismate in Arabidopsis  

作　　者：Michael P.Torrens-Spence Anastassia Bobokalonova Valentina Carballo Christopher MGlinkerman Toma(s)Pluskal Amber Shen Jing-Ke Weng 

机构地区：[1]Whitehead Institute for Biomedical Research,455 Main Street,Cambridge,MA 02142,USA [2]Department of Biology,Massachusetts Institute of Technology,Cambridge,MA 02139,USA

出　　处：《Molecular Plant》2019年第12期1577-1586,共10页分子植物（英文版）

基　　金：This work was supported by the Pew Scholar Program in the Biomedical Sciences,the Searle Scholars Program,and the National Science Foundation(CHE-1709616).

摘　　要：Salicylic acid(SA)is an important phytohormone mediating both local and systemic defense responses in plants.Despite over half a century of research,how plants biosynthesize SA remains unresolved.In Arabidop-sis,a major part of SA is derived from isochorismate,a key intermediate produced by the isochorismate syn-thase,which is reminiscent of SA biosynthesis in bacteria.Whereas bacteria employ an isochorismate pyru-vate lyase(IPL)that catalyzes the turnover of isochorismate to pyruvate and SA,plants do not contain an IPL ortholog and generate SA from isochorismate through an unknown mechanism.Combining genetic and biochemical approaches,we delineated the SA biosynthetic pathway downstream of isochorismate in Ara-bidopsis.We found that PBS3,a GH3 acyl adenylase-family enzyme important for SA accumulation,catalyzes ATP-and Mg2+-dependent conjugation of L-glutamate primarily to the 8-carboxyl of isochorismate and yields the key SA biosynthetic intermediate,isochorismoyl-glutamate A.Moreover,we discovered that EPS1,a BAHD acyltransferase-family protein with a previously implicated role in SA accumulation upon pathogen attack,harbors a noncanonical active site and an unprecedented isochorismoyl-glutamate A pyruvoyl-glutamate lyase activity that produces SA from the isochorismoyl-glutamate A substrate.Together,PBS3 and EPS1 form a two-step metabolic pathway to produce SA from isochorismate in Arabidopsis,which is distinct from how SA is biosynthesized in bacteria.This study closes a major knowledge gap in plant SA meta-bolism and would help develop new strategies for engineering disease resistance in crop plants.

关 键 词：salicylic ACID PBS1 EPS1 isochorismic ACID PLANT DEFENSE PLANT HORMONE 

分 类 号：O63[理学—高分子化学]