An <i>Arabidopsis thaliana</i> gene for methylsalicylate biosynthesis, identified by a biochemical genomics approach, has a role in defense

Emission of methylsalicylate (MeSA), and occasionally of methylbenzoate (MeBA), from Arabidopsis thaliana leaves was detected following the application of some forms of both biotic and abiotic stresses to the plant. Maximal emission of MeSA was observed following alamethicin treatment of leaves. A gene (AtBSMT1) encoding a protein with both benzoic acid (BA) and salicylic acid (SA) carboxyl methyltransferase activities was identified using a biochemical genomics approach. Its ortholog (AlBSMT1) in A. lyrata, a close relative of A. thaliana, was also isolated. The AtBSMT1 protein utilizes SA more efficiently than BA, whereas AlBSMT1 catalyzes the methylation of SA less effectively than that of BA. The AtBSMT1 and AlBSMT1 genes showed expression in leaves under normal growth conditions and were more highly expressed in the flowers. In A. thaliana leaves, the expression of AtBSMT1 was induced by alamethicin, Plutella xylostella herbivory, uprooting, physical wounding, and methyl jasmonate. SA was not an effective inducer. Using a beta-glucuronidase (GUS) reporter approach, the promoter activity of AtBSMT1 was localized to the sepals of flowers, and also to leaf trichomes and hydathodes. Upon thrip damage to leaves, AtBSMT1 promoter activity was induced specifically around the lesions.