Expansion and functional divergence of terpene synthase genes in angiosperms: a driving force of terpene diversity

Angiosperms are prolific producers of structurally diverse terpenes, which are essential for plant defense responses, as well as the formation of floral scents, fruit flavors, and medicinal constituents. Terpene synthase genes (TPSs) play crucial roles in the biosynthesis of terpenes. This study specifically focuses on the catalytic products of 222 functionally characterized TPSs in 24 angiosperms, which mainly comprise monoterpenes, sesquiterpenes, diterpenes, and sesterterpene. Our systematic analysis of these TPSs uncovered a significant expansion of the angiosperm-specific TPS-a, b, and g subfamilies in comparison to the TPS-e/f and c subfamilies. The expanded subfamilies can be further partitioned into distinct branches, within which considerable functional innovation and diversification have been observed. Numerous TPSs exhibit bifunctional or even trifunctional activities in vitro, yet they exhibit only a single activity in vivo, which may be largely determined by their inherent properties, subcellular localization, and the availabilities of endogenous substrates. Additionally, we explored the biological functions of terpenes in various organs and tissues of angiosperms. We propose that the expansion and functional divergence of TPSs contribute to the adaptability and diversity of angiosperms, facilitating the production of a broad spectrum of terpenes that enable diverse interactions with the environment and other organisms. Our findings provide a foundation for comprehending the correlation between the evolutionary features of TPSs and the diversity of terpenes in angiosperms, which is significant for terpene biosynthesis research.