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.

Terpenes are specialized metabolites ubiquitously produced by plants via the action of terpene synthases (TPSs). There are enormous variations in the types and amounts of terpenes produced by individual species. To understand the mechanisms responsible for such vast diversity, here we investigated the origin and evolution of a cluster of tandemly arrayed TPS genes in Oryza. In the Oryza species analyzed, TPS genes occur as a three-TPS cluster, a two-TPS cluster, and a single TPS gene in five, one, and one species, respectively. Phylogenetic analysis revealed the origins of the two-TPS and three-TPS clusters and the role of species-specific losses of TPS genes. Within the three-TPS clusters, one orthologous group exhibited conserved catalytic activities. The other two groups, both of which contained pseudogenes and/or nonfunctional genes, exhibited distinct profiles of terpene products. Sequence and structural analyses combined with functional validation identified several amino acids in the active site that are critical for catalytic activity divergence of the three orthologous groups. In the five Oryza species containing the three-TPS cluster, their functional TPS genes showed both conserved and species-specific expression patterns in insect-damaged and untreated plants. Emission patterns of volatile terpenes from each species were largely consistent with the expression of their respective TPS genes and the catalytic activities of the encoded enzymes. This study indicates the importance of combinatorial evolution of TPS genes in determining terpene variations among individual species, which includes gene duplication, retention/loss/degradation of duplicated genes, varying selection pressure, retention/divergence in catalytic activities, and divergence in expression regulation.

Comprehensive genomic analysis and experimental verification provide conclusive evidence that red algal terpenes are biosynthesized by microbial-type terpene sy

Clematis florida is a popular ornamental vine species known for diverse colors and shapes of its flowers but not for scent. Here we investigated the composition and biosynthesis of floral scent in ‘Kaiser’, a fragrant cultivar of C. florida that has sterile flowers. Volatile profiling revealed that flowers of ‘Kaiser’ emit more than 20 compounds, with monoterpenes being most abundant. Among the three floral organs, namely sepals, transformed-petals, and ovaries, ovaries had the highest rates of total volatile emission. To determine the molecular mechanism underlying floral scent biosynthesis in ‘Kaiser’, we sequenced a flower transcriptome and searched the transcriptome for terpene synthase genes (TPSs), which are key genes for terpene biosynthesis. Among the TPS genes identified, three were putative intact full-length genes and were designated CfTPS1, CfTPS2, and CfTPS3. Phylogenetic analysis placed CfTPS1, CfTPS2, and CfTPS3 to the TPS-g, TPS-b, and TPS-a subfamily, respectively. Through in vitro enzyme assays with Escherichia coli-expressed recombinant proteins, both CfTPS1 and CfTPS2 were demonstrated to catalyze the conversion of geranyl diphosphate to linalool, the most abundant constituent of C. florida floral scent. In addition, CfTPS1 and CfTPS2 produced the sesquiterpene nerolidol from (E,E)-farnesyl diphosphate. CfTPS3 showed sesquiterpene synthase activity and produced multiple products in vitro. All three CfTPS genes showed higher levels of expression in sepals than those in transformed-petals and ovaries. Our results show that despite being sterile, the flowers of ‘Kaiser’ have normal mechanisms for floral scent biosynthesis that make the flowers fragrant.

Although the petals of Rosa rugosa are rich in flavonoids and their bioactivity has a significant impact on human health, the flavonoid content decreases during flower development. In this study, R. rugosa ‘Feng hua’ was used to investigate the effects of the melatonin foliar spray on enhancing the quality of rose by focusing on major flavonoids. The results showed that the contents of total flavonoids in rose petals at the full bloom stage induced by melatonin obeyed a bell-shaped curve, with a maximum at 0.3 mM, indicating the concentration-dependent up-regulation of flavonoid biosynthesis. In the treatment with 0.3 mM melatonin, metabolomic analyses showed that the concentrations of ten main flavonoids were identified to be increased by melatonin induction, with high levels and increases observed in three flavonols and two anthocyanins. KEGG enrichment of transcriptomic analysis revealed a remarkable enrichment of DEGs in flavonoid and flavonol biosynthesis, such as Rr4CL, RrF3H, and RrANS. Furthermore, functional validation using virus-induced gene silencing technology demonstrated that Rr4CL3 is the crucial gene regulating flavonoid biosynthesis in response to the stimulant of melatonin. This study provides insights into the exogenous melatonin regulation mechanism of biosynthesis of flavonoids, thereby offering potential industrial applications.