Identification of a methyl jasmonate‐responsive region in the promoter of a lipoxygenase 1 gene expressed in barley grain

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Abstract
A genomic DNA fragment was isolated containing 5′ upstream sequences and part of the open reading frame corresponding to the lipoxygenase 1 cDNA (LoxA) expressed in barley grains during development and germination. Lox1 transcription was shown to be methyl jasmonate (MeJA)‐ and wound‐inducible in leaves, but Lox1 transcripts were not detected in mildew‐infected leaves, although this is a commonly observed response to pathogenic attack in various plants. Transient gene expression assays were used to identify a promoter region involved in MeJA‐responsive expression. Analysis of 5′ and 3′ promoter deletions indicated that sequences between −363 and −294 conferred MeJA‐responsive expression. Deletions/replacements covering this part of the promoter further defined a MeJA‐responsive region between −331 and −291. Insertion of the region −328 to −293 into the constitutive CaMV 35S promoter conferred MeJA‐responsive expression. The 36 bp fragment contains the motif TGACG as inverted repeats, which has been previously identified as a binding site for bZIP transactivating factors. Site‐directed mutagenesis on these TGACG motifs abolished MeJA‐responsive expression, clearly identifying them as MeJA‐responsive elements. Sequence comparisons found no similar motif in other characterized promoters of MeJA‐inducible genes, but suggested a common spatial structure which may serve as a binding site for transacting factors involved in the MeJA signal transduction pathway.

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