Monoterpene geraniol produced by rice terpene synthase 21 suppresses the expression of cell-division related genes in the rice bacterial pathogen, Xanthomonas oryzae pv. oryzae

Abstract

Plant volatile compounds such as monoterpenes and sesquiterpenes represent some of the classes of plant volatile compounds and they are involved in the plant defense responses. They are synthesized by terpene synthases (TPSs). The rice genome has reportedly more than 30 TPSs genes and several of them are regulated by a plant hormone, jasmonic acid (JA). In the present study, we analyzed a rice terpene synthase, OsTPS21, and investigated its potential antibacterial effects against Xanthomonas oryzae pv. oryzae (Xoo), which causes rice bacterial blight. OsTPS21 was localized in the chloroplast and produced a monoterpene geraniol as a monoterpene synthase. In addition, OsTPS21 did not exhibit any activity as a sesquiterpene synthase. The amount of geraniol in rice increased along with the upregulation of OsTPS21 after JA treatment. Geraniol had a negative effect on the growth of Xoo. The growth inhibition of Xoo by geraniol was caused by the suppression of expression of the cell-division-related genes of Xoo and not by damage to Xoo cell membranes. The results suggest that geraniol plays an important role in JA-induced resistance against Xoo and that it functions as an antibacterial compound in rice.