Terpenoid Secondary Metabolites in Bryophytes: Chemical Diversity, Biosynthesis and Biological Functions

Bryophytes are close extant relatives of the ancestral land plant. As such, they have retained many innovations that had enabled the adaptation of early land plants to the terrestrial environment. One of such important innovations is the elaboration of an enormously diverse array of secondary metabolites. This article reviews current knowledge of terpenoid secondary metabolites, which constitute the largest family of plant metabolites, in bryophytes from three perspectives: chemical diversity, biosynthesis, and biological functions. The diversity of terpenoids in bryophytes, particularly in liverworts, is enormously rich. More than 1600 terpenoids have been reported from this plant group. While many terpenoids are observed in both bryophytes and seed plants, some are unique to bryophytes. It is just the beginning for us to understand the molecular and biochemical basis underlying terpenoid biosynthesis in bryophytes. Compared to seed plants, which have only one type of terpene synthase genes, so-called typical plant terpene synthase genes, bryophytes employ not only typical plant terpene synthase genes but also another class of terpene synthase genes called microbial-terpene synthase-like (MTPSL) genes for terpenoid biosynthesis. Biochemical studies suggest the MTPSLs are largely responsible for the terpenoid diversity in bryophytes, particularly sesquiterpenes and monoterpenes. Existing literature indicates that terpenoids made by bryophytes have important functions in diverse biological and ecological processes, particularly as defenses against biotic and abiotic stresses. The continued development of genomic resources and molecular tool kit for bryophytes will accelerate characterization of terpenoids biosynthesis and their biological functions in this important lineage of plants.