Biochemical and functional characterization of two microbial type terpene synthases from moss Stereodon subimponens

Terpenes constitute a large class of plant secondary metabolites. Usually, there is only one type of terpene synthase in seed plants, which is called typical plant terpene synthase. Currently, as a new family of plant terpene synthases, microbial terpene synthase-like (MTPSL) is identificated in nonseed plants. However, our knowledge about the biological function of most MTPSLs in nonseed plants is very limited. Here, we investigated the biochemical and functional characterization of the enzymes encoded by two MTPSLs from moss Stereodon subimponens, SsMTPSL1 and SsMTPSL2. A phylogenetic tree analysis showed that SsMTPSL1 and SsMTPSL2 are homologous to AaMTPSL1, AaMTPSL3, ApMTPSL1, and ApMTPSL3 from hornworts. The enzyme activity experiment demonstrated that SsMTPSL1 has monoterpene synthase and sesquiterpene synthase activity, and SsMTPSL2 has monoterpene synthase activity. Next, we selected SsMTPSL1 to study its biochemical functions. Anti-bacterial activity test in vitro showed that the products of SsMTPSL1 have an anti-bacterial effect on Escherichia coli, Pseudomonas syringae pv. Tomato DC3000 (Pst DC3000), and Staphylococcus aureus. To further understand the function of SsMTPSL1, the transgenic Arabidopsis thaliana plant of SsMTPSL1 is inoculated by Pst DC3000, and the result showed that SsMTPSL1 enhances the resistance of A. thaliana to Pst DC3000. All in all, this study provides new information about the functions of moss MTPSLs.