Isolation and Characterization of a Jasmonic Acid Carboxyl Methyltransferase Gene from Hot Pepper (Capsicum annuum L.)

Methyl jasmonate, the methyl ester of jasmonic acid, is a volatile plant hormone that acts as an important cellular regulator, mediating diverse developmental processes and defense responses. Methyl jasmonate is synthesized by methylation of jasmonic acid; this reaction is catalyzed by jasmonic acid carboxyl methyltransferase (JMT). Although JMT cDNA had previously been described only for Arabidopsis thaliana, here we used PCR to isolate it from Capsicum annuum L. The 389-amino-acid sequence deduced for the JMT gene showed $ 92\% $ identity to that from A. thaliana. Southern blot analysis revealed that JMT is present in the genome as two copies. Our preliminary northern blot detected no JMT transcript, but, through RT-PCR and subsequent Southern blot analysis of products using gene-specific probes, we found that transcript levels increased after leaf-wounding. likewise, $10\muM$ methyl jasmonate induced JMT gene expression in leaves. Transcription levels began to increase 10 min after wounding, and were maintained for 1 to 4 h. Moreover, expression of the CaJMT and PIN2 genes was increased by both wounding and MeJA applications, but was not enhanced by treatment with $H_{2}O_{2}$.