Unraveling the evolutionary dynamics of the TPS gene family in land plants

Genetic variation in a tandemly duplicated TPS gene cluster contributes to the diversity of aroma in lychee fruit

Fruits undergo a similar ripening process, yet they exhibit a range of differences in color, taste, and shape, both across different species and within the same species. How does this diversity arise? We uncovered a conserved fruit ripening process in lychee fruit in which a NAC transcription factor, LcNAC1, acts as a master regulator. LcNAC1 regulates the expression of two terpene synthase genes, LcTPSa1 and LcTPSa2, which belong to a gene cluster consisting of four TPS genes. LcTPSa1-LcTPSa3 are responsible for catalyzing the production of farnesol, which in turn dictates the aromatic diversity in fruit of different lychee varieties. Through comparative, transcriptomic, and genomic analyses across various lychee varieties, we found these four TPS genes exhibit distinct expression levels due to natural genetic variation. These include copy number variations, presence/absence variations, insertions and deletions, and single nucleotide polymorphisms, many of which affect the binding affinity of LcNAC1. A single nucleotide mutation in LcTPSa1 caused a premature translational termination, resulting in a truncated version of the TPS protein, which surprisingly remains functional. All these genomic changes in the LcNAC1-regulated TPS genes are likely to contribute to the great aromatic diversity observed in lychee fruit. This diversification of fruit aroma in lychee varieties offers a compelling example of how species- or variety-specific traits evolve - the phenotypic diversity is primarily derived from natural genetic variation accumulated in downstream structural genes within an evolutionarily conserved regulatory circuit.

Advances in the Biosynthesis of Plant Terpenoids: Models, Mechanisms, and Applications

Plants have evolved complex terpene defenses. Terpenoids accumulate in plant tissues or release as volatile in response to ever-changing environment, playing essential roles in chemo-ecological functions as defense against pathogen and insect, improving pollination and seed dispersal, facilitation plant-to-plant communication. They are also gaining attention in pharmaceuticals, nutraceuticals, fragrance, and biofuels. Here, we highlight the recent progress in the fundamental pathways of terpenoid biosynthesis, key enzymes, and their corresponding genes involved in terpenoid synthesis. We identified the further exploration of biosynthetic networks and the development of novel terpenoid resources, proposed the need for further exploration of biosynthetic networks and the development of novel terpenoid resources. Based on that knowledge, future research should be directed towards the mechanisms governing terpenoid biosynthesis dependent environmental change and molecular breeding.

Revealing the molecular mechanism of biosynthesis and transcriptional regulation of PAs, caffeine and linalool globally under simulative stress in coffee plants

Coffee has become one of the most popular beverages worldwide due to the variety of bioactive compounds, which also play crucial roles against biotic and abiotic stresses. However, little is known about how these defensive compounds are produced in coffee. Here, we found that the whole biosynthetic pathways and the production of caffeine and proanthocyanidins (PAs) were promoted under Methyl Jasmonate (MeJA) treatment. Co-expression data showed that some transcription factors were shared by caffeine and PA regulation, and further several candidate caffeine regulators were identified. The biosynthesis of monoterpene linalool was also triggered by MeJA, and the functions of coffee linalool synthase were characterized. Evolution and expression analyses revealed that the expression variation of linalool synthase is likely the major reason for the low linalool content in coffee leaves, despite of the linalool synthase expansion in coffee genome. Additionally, the JA signaling key regulator MYC2 could directly bind to and activate the promoter of linalool synthase to regulate linalool biosynthesis.

Genome sequencing of three Polyscias species reveals common features in terpene synthase gene family evolution in these species

The genus Polyscias, part of the Araliaceae family, is known for its significant ornamental and medicinal value, as well as its rich variety of metabolites. These plants are primarily found in tropical regions, particularly in Southeast Asia and the Pacific islands. The diverse geographical environments have led to the emergence of many unique and endangered species, although there is limited genomic information available about them. In this study, we generated high-quality reference genomes for three endangered species: two that are endemic to Hawai'i, Polyscias cf. bisattenuata and Polyscias lallanii, and one more widespread species, Polyscias macgillivrayi. We identified a total of 51,083, 60,881, and 29,060 genes in these three species, respectively. Whole-genome duplication analysis indicated that all three species underwent a common duplication event. By examining the phylogenetic and structural characteristics of the terpene synthase gene family in these species and closely related species, we identified several gene clusters that play crucial roles in metabolite synthesis. A variety of mono- and sesquiterpenoids were detected, with several of these compounds having been validated in previous studies. Our findings provide a foundation for further genetic and biochemical investigations of Polyscias, which may aid in the conservation of these endangered species.

Genome-wide identification and evolution-profiling analysis of tps gene family in Camphora longepaniculata and screening of key TPS genes

Camphora longepaniculata is an important economic crop renowned for its rich volatile terpene compounds. Terpene synthases (TPS) are key enzymes in the biosynthesis of these compounds, playing significant roles in plant growth, development, and secondary metabolism. In this study, a total of 86 TPS genes were identified in Camphora longepaniculata, which were classified into five groups based on their evolutionary relationships. Analysis of cis-regulatory elements revealed associations between TPS genes and processes related to plant growth, development, and environmental stress responses. Gene Ontology (GO) enrichment analysis indicated that these TPS genes are predominantly linked to various enzymatic activities. Furthermore, analysis of duplication events revealed that tandem duplications (TD) and whole genome duplications (WGD) are major driving forces in the evolution of the TPS gene family. Notably, 18 TPS genes were found to be upregulated in high essential oil content varieties of Camphora longepaniculata. RT-qPCR validation further confirmed that TPS26, TPS28, and TPS47 exhibit upregulated expression during leaf development, highlighting their potential involvement in terpene biosynthesis during this crucial developmental stage. These findings lay a solid foundation for further exploration of the functions of TPS genes in Camphora longepaniculata.

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.

Plant specialized metabolism: Diversity of terpene synthases and their products

Terpenoids are ubiquitous to all kingdoms of life and are one of the most diverse groups of compounds, both structurally and functionally. Despite being derived from common precursors, isopentenyl diphosphate and dimethylallyl diphosphate, their exceptional diversity is partly driven by the substrate and product promiscuity of terpene synthases that produce a wide array of terpene skeletons. Plant terpene synthases can be subdivided into different subfamilies based on sequence homology and function. However, in many cases, structural architecture of the enzyme is more essential to product specificity than primary sequence alone, and distantly related terpene synthases can often mediate similar reactions. As such, the focus of this brief review is on some of the recent progress in understanding terpene synthase function and diversity.

Discovery of bifunctional diterpene cyclases/synthases in bacteria supports a bacterial origin for the plant terpene synthase gene family

Land plants are well-known producers of terpenoids that play diverse roles in plant-environment interactions. The vast chemical diversity of terpenoids is initiated by terpene synthases. Plants contain a distinct mid-sized terpene synthase gene family termed TPS, which appears to have an ancient origin in a fused bacterial Class I (di)terpene synthase (TS) and Class II diterpene cyclase (DTC), corresponding to the catalytically relevant α-domain and βγ-didomains, respectively. However, while such fused tridomain bifunctional (Class I/II) diterpene cyclases/synthases (DCSs) have been found in plants (and fungi), no examples have been reported from bacteria, leaving the origin of the fusion event initiating the TPS gene family opaque. Here, the discovery of such tridomain bifunctional DCSs in bacteria is reported. Extensive genome mining unearthed five putative bacterial DCSs, with biochemical characterization revealing the expected bifunctional activity for three. The most intriguing was CseDCS from Candidatus sericytochromatia bacterium, which produces ent-kaurene, an intermediate in plant hormone biosynthesis, as this is the hypothesized activity for the ancestral TPS. Unlike the extant functionally equivalent TPSs, it was possible to split CseDCS into separate, independently acting DTC and TS, with the first producing the expected ent-copalyl diphosphate (CPP), serving as a CPP synthase (CPS), while the second converts this to ent-kaurene, serving as a kaurene synthase (KS). Nevertheless, sequence alignment and mutation analysis revealed intriguing similarities between this cyanobacterial fused CPS-KS and functionally equivalent TPSs. Regardless of the exact relationship, the discovery of fused bifunctional DCSs in bacteria supports the hypothesized origin of the plant TPS family from such a bacterial gene.

Chemical diversity in angiosperms - monoterpene synthases control complex reactions that provide the precursors for ecologically and commercially important monoterpenoids

Monoterpene synthases (MTSs) catalyze the first committed step in the biosynthesis of monoterpenoids, a class of specialized metabolites with particularly high chemical diversity in angiosperms. In addition to accomplishing a rate enhancement, these enzymes manage the formation and turnover of highly reactive carbocation intermediates formed from a prenyl diphosphate substrate. At each step along the reaction path, a cationic intermediate can be subject to cyclization, migration of a proton, hydride, or alkyl group, or quenching to terminate the sequence. However, enzymatic control of ligand folding, stabilization of specific intermediates, and defined quenching chemistry can maintain the specificity for forming a signature product. This review article will discuss our current understanding of how angiosperm MTSs control the reaction environment. Such knowledge allows inferences about the origin and regulation of chemical diversity, which is pertinent for appreciating the role of monoterpenoids in plant ecology but also for aiding commercial efforts that harness the accumulation of these specialized metabolites for the food, cosmetic, and pharmaceutical industries.