C6-volatiles derived from the lipoxygenase pathway induce a subset of defense-related genes.
Six-Carbon (C6-) 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 microM concentrations of trans-2-hexenal induces several genes known to be involved in the plant's defense response, including phenylpropanoid-related 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 C6-related volatiles, as C8-, C9- 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 C6-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.
Bate
N J
NJ
Department of Molecular Biology and Genetics, University of Guelph, Ontario, Canada. baten@em.agr.c
Rothstein
S J
SJ
D000085:Acetates / Q000378:metabolism / Q000494:pharmacology; D000447:Aldehydes / Q000378:metabolism / Q000494:pharmacology; D000872:Anthocyanins / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D003517:Cyclopentanes / Q000378:metabolism / Q000494:pharmacology; D017931:DNA Primers / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D000441:Hexanols / Q000378:metabolism / Q000494:pharmacology; D008084:Lipoxygenase / Q000378:metabolism*; D054883:Oxylipins; D015398:Signal Transduction
D000085:Acetates; D000447:Aldehydes; D000872:Anthocyanins; D003517:Cyclopentanes; D017931:DNA Primers; D000441:Hexanols; D054883:Oxylipins; C051750:2-hexenal; C072239:methyl jasmonate; D008084:Lipoxygenase