Identification and characterization of salicylic acid carboxyl methyltransferase gene in rice

Abstract

Methyl esters such as methyl jasmonate, methyl salicylate, and methyl benzoate constitute volatile floral scent, and some of them are known to act as important cellular regulators mediating diverse responses. Methyltransferase catalyze the formation of methyl esters using carboxylic acid-bearing substrates as methyl acceptors. Through the NCBI rice genome database search, we identified a rice gene highly homologous to Arabidopsis jasmonic acid carboxyl methyltransferase gene. Corresponding cDNA clone (OsSAMT) was obtained from the MAFF Gene Bank in Japan. The cDNA was expressed in E. coli was examined enzymatic characteristics of the protein product. The expressed protein exhibits SAMT (SAM:salicylic acid carboxyl methyltransferase) and BAMT (SAM:benzoic acid carboxyl methyltransferase) activities in vitro. Furthermore, the transgenic Arabidopsis overexpressing the gene was generated to study its physiological function(s). The transgenic plant contained about 2-fold enhanced level of methyl salicylate compared to wild type. In this transgenic plants, expression of PR1 that are known as a response to salicylic acid was not induced by salicylic acid. These data suggest that salicylic acid is the active form and MeSA mainly act as airborne signal in plants defense. Recently, Feng Chen et al. observed that AtBSMT1 induced by mehyl jasmonate. OsSAMT might participated in the antagonistic effect of jasmonate on the salicylate signaling.