Concepedia

Analysis of a Chemical Plant Defense Mechanism in Grasses

Monika Frey, Paul Chomet, Erich Glawischnig, Cornelia Stettner, Sebastian Grün, Albert Winklmair, Wolfgang Eisenreich, Adelbert Bacher, Robert Meeley, Steven P. Briggs,

Science · 1997 · 697 citations · 25 references

DOI

TL;DR

In Gramineae, the cyclic hydroxamic acids DIBOA and DIMBOA contribute to defense against insects and pathogens, and five genes (Bx1–Bx5) are required for DIBOA biosynthesis in maize. Bx1 encodes a tryptophan synthase α homolog that diverts indole toward secondary metabolites, while Bx2–Bx5 encode cytochrome P450 monooxygenases that perform four hydroxylations and a ring expansion to produce DIBOA. In vitro studies confirmed the functions of the five Bx genes clustered on chromosome 4.

Abstract

In the Gramineae, the cyclic hydroxamic acids 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) form part of the defense against insects and microbial pathogens. Five genes, Bx1 through Bx5 , are required for DIBOA biosynthesis in maize. The functions of these five genes, clustered on chromosome 4, were demonstrated in vitro. Bx1 encodes a tryptophan synthase α homolog that catalyzes the formation of indole for the production of secondary metabolites rather than tryptophan, thereby defining the branch point from primary to secondary metabolism. Bx2 through Bx5 encode cytochrome P450–dependent monooxygenases that catalyze four consecutive hydroxylations and one ring expansion to form the highly oxidized DIBOA.