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

Abstract

SummaryEmission 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 identi®ed 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 ef®ciently 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¯owers. 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 b-glucuronidase (GUS) reporter approach, the promoter activity of AtBSMT1 was localized to the sepals of¯owers, and also to leaf trichomes and hydathodes. Upon thrip damage to leaves, AtBSMT1 promoter activity was induced speci®cally around the lesions.

Biosynthesis and emission of insect-induced methyl salicylate and methyl benzoate from rice

“…Methyl salicylate (MeSA) is a frequent constituent of insect-induced plant volatiles. It has been detected in the headspace of many insect-infested plants, such as lima bean [2], Arabidopsis [5], tomato [1], and soybean [47]. When tested in its pure, synthetic form, MeSA can attract several types of carnivores [8,10,47], suggesting that MeSA, singly or in combination with other volatiles, is an active signal for indirect defense of tested plants.…”

“…Methyl benzoate is structurally highly similar to MeSA. It is occasionally detected from insect-damaged plants [5].…”

“…Such an enzyme has been named BSMT. Genes encoding SAMT, BAMT and BSMT have been isolated and biochemically characterized from a number of plant species that include Clarkia breweri [32], snapdragon (Antirrhinum majus) [24], Stephanotis floribunda [29], Nicotiana suaveolens [29], and Arabidopsis [5]. The majority of these genes are involved in producing MeSA and/or MeBA as a floral scent compound.…”

“…The majority of these genes are involved in producing MeSA and/or MeBA as a floral scent compound. The Arabidopsis gene, AtBSMT1, is the only gene involved in herbivore-induced MeSA and MeBA production [5]. Interestingly, AtBSMT1 is phylogenetically more closely related to JA methyltransferase (JMT) than to other SAMTs, although it does not use JA as substrate [5].…”

“…The Arabidopsis gene, AtBSMT1, is the only gene involved in herbivore-induced MeSA and MeBA production [5]. Interestingly, AtBSMT1 is phylogenetically more closely related to JA methyltransferase (JMT) than to other SAMTs, although it does not use JA as substrate [5]. Whether the production of insect-induced MeSA in other plant species is catalyzed by SABATH genes, and if so, how those genes are related, remains unknown.…”