Overexpression of salicylic acid carboxyl methyltransferase reduces salicylic acid-mediated pathogen resistance in Arabidopsis thaliana
We cloned a salicylic acid/benzoic acid carboxyl methyltransferase gene, OsBSMT1, from Oryza sativa. A recombinant OsBSMT1 protein obtained by expressing the gene in Escherichia coli exhibited carboxyl methyltransferase activity in reactions with salicylic acid (SA), benzoic acid (BA), and de-S-methyl benzo(1,2,3)thiadiazole-7-carbothioic acid (dSM-BTH), producing methyl salicylate (MeSA), methyl benzoate (MeBA), and methyl dSM-BTH (MeBTH), respectively. Compared to wild-type plants, transgenic Arabidopsis overexpressing OsBSMT1 accumulated considerably higher levels of MeSA and MeBA, some of which were vaporized into the environment. Upon infection with the bacterial pathogen Pseudomonas syringae or the fungal pathogen Golovinomyces orontii, transgenic plants failed to accumulate SA and its glucoside (SAG), becoming more susceptible to disease than wild-type plants. OsBSMT1-overexpressing Arabidopsis showed little induction of PR-1 when treated with SA or G. orontii. Notably, incubation with the transgenic plant was sufficient to trigger PR-1 induction in neighboring wild-type plants. Together, our results indicate that in the absence of SA, MeSA alone cannot induce a defense response, yet it serves as an airborne signal for plant-to-plant communication. We also found that jasmonic acid (JA) induced AtBSMT1, which may contribute to an antagonistic effect on SA signaling pathways by depleting the SA pool in plants.
KeywordsArabidopsis Methyl salicylate (MeSA) Plant disease resistance Rice SA carboxyl methyltransferase Salicylic acid (SA)
This work was supported by grants from the Crop Functional Genomics Center (CG2112 to JJC and CG2111 to JK) and the Korea Research Foundation (KRF-2004-005-F00013 to YDC). Financial support, including graduate research assistantships to YJK and CJ, from the Brain Korea 21 project of the Ministry of Education is also acknowledged. Special thanks are due to Professors In Gyu Hwang and Soon Ok Kim (Seoul National University) for the identification of Golovinomyces orontii.
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