Disruption of allene oxide cyclase in maize reveals the necessity of enzymatically produced 12-OPDA for the induction of jasmonic acid during herbivory

Abstract

Allene oxide cyclase (AOC) catalyzes the formation of 12-oxo-phytodienoic acid (12-OPDA) and represents an understudied step in jasmonate biosynthesis. Here the effects of eliminating AOC function in maize (Zea mays) are investigated. Gene editing was used to disrupt a pair of redundant AOC-coding genes, and mutants were analyzed with targeted metabolomics in a biochemical characterization of jasmonate deficiency. Our findings confirm essential roles for AOC in male flower development and resistance to biotic stresses. Metabolomic examinations show that AOC deficiency leads to a 90% reduction in 12-OPDA and a 99% reduction in jasmonic acid (JA) and JA-Isoleucine after treatment with fall armyworm. The presence of 12-OPDA in equal proportions of cis-(+) and cis-(-) stereochemical isomers indicates nonenzymatic allene oxide cyclization in the absence of functional AOC. This residual 12-OPDA is not converted into JA or other downstream jasmonates during herbivory, revealing the necessity of enzymatic cyclization of allene oxide by AOC for insect-induced JA and JA-dependent defense responses. The AOC-deficient mutants developed here provide a new tool for investigating the roles of jasmonates in maize.

Keywords: AOC; Cochliobolus heterostrophus (southern corn leaf blight); Spodoptera frugiperda (fall armyworm); Zea mays; auxin; jasmonates; oxylipin; salicylic acid; tasselseed.