Epoxide hydrolase: a mRNA induced by the fungal pathogen Alternaria alternata on rough lemon (Citrus jambhiri Lush).

An expression profile of genes induced by non-pathogenic Alternaria alternata on rough lemon leaves was obtained by sequencing 500 subtractive PCR clones generated from mRNA of leaves inoculated with the fungus after subtraction with that of non-inoculated leaves. About 6% of the cDNA sequences had homology to known putative defense-related genes including epoxide hydrolase. A full-length cDNA (951 bp) from rough lemon that encoded epoxy hydrolase was isolated by random amplification of cDNA ends (RACEs), based on sequence information from subtractive PCR, and designated as RlemEH. The product of this gene expressed with an in vitro translation system with Escherichia coli also had activity of a soluble type of epoxide hydrolase. The transcript of rough lemon RlemEH was not detected in flowers, fruits, stems or leaves, but was induced after inoculation of leaves with conidia of Alternaria alternata, wounding, or treatment with C6 volatiles, including trans-2-hexenol and cis-3-hexenol, and methyl jasmonate. The response of the epoxide hydrolase gene correlated well with the activation of defense mechanisms induced in plant-fungus interactions.