Lipoxygenase H1 gene silencing reveals a specific role in supplying fatty acid hydroperoxides for aliphatic aldehyde production.

Lipoxygenases catalyze the formation of fatty acid hydroperoxide precursors of an array of compounds involved in the regulation of plant development and responses to stress. To elucidate the function of the potato 13-lipoxygenase H1 (LOX H1), we have generated transgenic potato plants with reduced expression of the LOX H1 gene as a consequence of co-suppression-mediated gene silencing. Three independent LOX H1-silenced transgenic lines were obtained, having less than 1% of the LOX H1 protein present in wild-type plants. This depletion of LOX H1 has no effect on the basal or wound-induced levels of jasmonates derived from 13-hydroperoxylinolenic acid. However, LOX H1 depletion results in a marked reduction in the production of volatile aliphatic C6 aldehydes. These compounds are involved in plant defense responses, acting as either signaling molecules for wound-induced gene expression or as antimicrobial substances. LOX H1 protein was localized to the chloroplast and the protein, expressed in Escherichia coli, showed activity toward unesterified linoleic and linolenic acids and plastidic phosphatidylglycerol. The results demonstrate that LOX H1 is a specific isoform involved in the generation of volatile defense and signaling compounds through the HPL branch of the octadecanoid pathway.