Functional Characterization of Terpene Synthases from Masson Pine (Pinus massoniana) under Feeding of Monochamus alternatus Adults

Conifers have evolved sophisticated terpenoid defenses for protection against herbivores and pathogens. Pinus massoniana Lamb. is the most widely distributed pioneer afforestation and resin tree species in China, but is seriously harmed by pine wilt disease. Monochamus alternatus is the main vector of pine wilt disease in China. Monoterpenes, sesquiterpenes and diterpenes, the main secondary defensive compounds of P. massoniana, are catalyzed by different terpene synthases (TPSs), which participate in the important defense pathways against external biotic and abiotic stresses. Here, we aimed to identify the terpene synthases (TPSs) in P. massoniana, responding to the feeding of M. alternatus, and to characterize the functions and products of the mono-TPSs. We identified six differentially expressed TPS genes in the P. massoniana fed upon by M. alternatus, including four mono-TPS and two sesqui-TPS genes. The functions of the four mono-TPSs were verified by analysis of the main product and by-products of these mono-TPSs. (+)-α-Pinene, (−)-α-pinene, and limonene were the major products of TPS (+)-α-pinene, TPS (−)-α-pinene, and TPS limonene, respectively, but TPS (−)-β-pinene only catalyzed a trace amount of (−)-β-pinene in the products. Our findings shed light on the potential relationships between the structure of terpene synthases and their corresponding products.