C₆‐volatiles derived from the lipoxygenase pathway induce a subset of defense‐related genes

Abstract

SummarySix-Carbon (C 6 -) volatiles, including the aldehydes trans-2-hexenal, hexanal and cis-3-hexenal, as well as their corresponding alcohols, are produced from damaged or wounded plant tissue as a product of the enzymatic activity of hydroperoxide lyase (HPL), a component of the lipoxygenase (LOX) pathway. Aerial treatment of Arabidopsis seedlings with 10 µM concentrations of trans-2-hexenal induces several genes known to be involved in the plant's defense response, including phenylpropanoidrelated genes as well as genes of the LOX pathway. Genes encoding the pathogenesis-related proteins PR-1 or PR-2, however, were not induced. Trans-2-hexenal induction thus closely mimics the group of genes induced by methyl jasmonate (MeJA), also a LOX-derived volatile. However, unlike MeJA, trans-2-hexenal did not induce hydroxymethylglutaryl-coenzyme A reductase (HMGR) or thionin2-1. The inductive effect seemed to be limited to C 6 -related volatiles, as C 8 -, C 9 -and other related volatiles did not induce LOX mRNA levels. As has been demonstrated for MeJA, trans-2-hexenal quantitatively reduced wild-type seed germination. Trans-2-hexenal also reduced the germination frequency of the MeJA resistant Arabidopsis mutant, jar1-1, supporting the notion that trans-2-hexenal and MeJA are recognized via different mechanisms. In addition, trans-2-hexenal had a moderate inhibitory effect on root length relative to similar concentrations of MeJA and was approximately 10-fold less effective than MeJA at inducing anthocyanin accumulation in Arabidopsis seedlings. These results suggest that C 6 -volatiles of the LOX pathway act as a wound signal in plants, but result in a moderate plant response relative to MeJA at both the physiological and molecular level.

Priming of Wheat with the Green Leaf Volatile Z-3-Hexenyl Acetate Enhances Defense against Fusarium graminearum But Boosts Deoxynivalenol Production

“…Other studies found minor inductions of gene expression after treatment with GLVs. For example, Bate and Rothstein (1998) exposed Arabidopsis seedlings to the GLV E-2-HAL. They found induction of PAL, LOX, and AOS but no induction of PR1 and PR2.…”

Lipid metabolism in arbuscular mycorrhizal roots of Medicago truncatula

“…syringae, whereas a virulent strain did not lead to such an increase (Croft et al, 1993). Different C6-volatiles have been shown to induce defence related genes and to stimulate phytoalexin accumulation (Zeringue, 1992;Bate and Rothstein, 1998). In transgenic potato plants lacking HPL transcript an increase in aphid performance was observed (Vancanneyt et al, 2001).…”

The Role of Indole and Other Shikimic Acid Derived Maize Volatiles in the Attraction of Two Parasitic Wasps

“…These derive from at least three pathways. Green leaf volatiles are products of the enzymatic activity of hydroperoxide lyase (HPL), a component of the lipoxygenase (LOX) pathway, which results in multiple rearrangement of (Z)-3-hexenal (Bate and Rothstein, 1998;Blee, 1998). Terpenoids are synthesized via the isopentenyl pyrophosphate (IPP) intermediate following the classical mevalonate pathway or via an alternative IPP pathway with glyceraldehyde-3-phosopate and pyruvate identified as the direct precursors of IPP (Lichtenthaler et al, 1997).…”