Divinyl ether synthesis in garlic bulbs

M Stumpe,C Gobel,J.-G Carsjens,I Feussner

doi:10.1093/jxb/ern010

Abstract

Formation of 13-lipoxygenase-derived divinyl ethers has been described in garlic bulbs. Here, the identification of a cDNA from garlic is described, which encodes for an enzyme that corresponds to divinyl ether synthases (DES). The recombinant protein was expressed in Escherichia coli and shown to metabolize 13-hydroperoxy as well as 9-hydroperoxy linole(n)ic acid to etherole(n)ic and colnele(n)ic acid, respectively. This biochemical feature classifies it as a member of the CYP74C subfamily of cytochrome P-450 enzymes. Product analysis after incubation of purified recombinant enzyme and fatty acid hydroperoxides revealed the formation of a mixture of different cis/trans isomers with one isomer often dominant. RNA blot analyses showed a constitutive expression of DES transcripts predominant in below-ground organs of garlic. By exogenous application of salicylic acid and sorbitol, but not by methyljasmonate, the transcript was also induced in leaves. Whereas the prominent divinyl ether in garlic was the 13-lipoxygenase-derived etheroleic acid, analysis of transgenic Arabidopsis expressing garlic DES showed that 9-lipoxygenase-derived colnelenic acid dominated 24 h after wounding. These data indicate that the product pattern of this DES from garlic depends on the substrate availability and that the enzyme is the first member in the group of 9/13-DES.

Highlights

Divinyl ethers are a group of oxidized fatty acid derivatives containing ether oxygen within their hydrocarbon chains (Blee, 1998)
allene oxide synthase (AOS) is part of the pathway leading to the formation of jasmonic acid (JA), a plant hormone involved in plant development and stress responses (Wasternack and Hause, 2002)
Related activities leading to formation of EA and etherolenic acid (EnA) were described from garlic and different Ranunculaceae species and a number of algae (Grechkin et al, 1995; Hamberg, 2002, 2004)

Summary

Introduction

Divinyl ethers are a group of oxidized fatty acid derivatives containing ether oxygen within their hydrocarbon chains (Blee, 1998). In plants they may be produced by sequential action of a lipoxygenase (LOX) and a divinyl ether synthase (DES) (Grechkin, 1998). The DES responsible for the CA and CnA formation in potato and tomato have been cloned and characterized (Itoh and Howe, 2001; Stumpe et al, 2001) The analysis of their sequences led to classification of the enzymes within the group of cytochrome P450 enzymes, in the CYP74D subfamily. HPL cleave hydroperoxide substrates into short chain aldehydes and x-oxo fatty acids

Methods

Results

Conclusion