Medicago TERPENE SYNTHASE 10 Is Involved in Defense Against an Oomycete Root Pathogen.

In nature, plants interact with numerous beneficial or pathogenic soil-borne microorganisms. Plants have developed various defense strategies to expel pathogenic microbes, some of which function soon after pathogen infection. We used and its oomycete pathogen to elucidate early responses of the infected root. causes root rot disease in legumes and is a limiting factor in legume production. Transcript profiling of seedlings and adult plant roots inoculated with zoospores for 2 h revealed specific upregulation of a gene encoding a putative sesquiterpene synthase ( TERPENE SYNTHASE 10 [MtTPS10]) in both developmental stages. was specifically expressed in roots upon oomycete infection. Heterologous expression of in yeast led to production of a blend of sesquiterpenes and sesquiterpene alcohols, with NMR identifying a major peak corresponding to himalachol. Moreover, plants carrying a tobacco () retrotransposon insertion in lacked the emission of sesquiterpenes upon infection, supporting the assumption that the identified gene encodes a multiproduct sesquiterpene synthase. plants and plants with reduced transcript levels created by expression of an -artificial microRNA in roots were more susceptible to infection than were the corresponding wild-type plants and roots transformed with the empty vector, respectively. Sesquiterpenes produced by expression of in yeast also inhibited mycelial growth and zoospore germination. These data suggest that sesquiterpene production in roots by MtTPS10 plays a previously unrecognized role in the defense response of against .