Identification of a beta-glucosidase hydrolyzing tuberonic acid glucoside in rice (Oryza sativa L.)

Tuberonic acid (TA) and its glucoside (TAG) have been isolated from potato (Solanum tuberosum L.) leaflets and shown to exhibit tuber-inducing properties. These compounds were reported to be biosynthesized from jasmonic acid (JA) by hydroxylation and subsequent glycosylation, and to be contained in various plant species. Here we describe the in vivo hydrolytic activity of TAG in rice. In this study, the TA resulting from TAG was not converted into JA. Tuberonic acid glucoside (TAG)-hydrolyzing beta-glucosidase, designated OsTAGG1, was purified from rice by six purification steps with an approximately 4300-fold purification. The purified enzyme migrated as a single band on native PAGE, but as two bands with molecular masses of 42 and 26 kDa on SDS-PAGE. Results from N-terminal sequencing and peptide mass fingerprinting of both polypeptides suggested that both bands were derived from a single polypeptide, which is a member of the glycosyl hydrolase family 1. In the native enzyme, the K(m) and V(max) values of TAG were 31.7 microM and 0.25 microkatal/mg protein, OsTAGG1 preferentially hydrolyzed TAG and methyl TAG. Here we report that OsTAGG1 is a specific beta-glucosidase hydrolyzing TAG, which releases the physiologically active TA.