Identification of Three Monofunctional Diterpene Synthases with Specific Enzyme Activities Expressed during Heartwood Formation in Western Redcedar (Thuja plicata) Trees

Functional identification of specialized diterpene synthases from Chamaecyparis obtusa and C. obtusa var. formosana to illustrate the putative evolution of diterpene synthases in Cupressaceae

Chamaecyparis obtusa and C. obtusa var. formosana of the Cupressaceae family are well known for their fragrance and excellent physical properties. To investigate the biosynthesis of unique diterpenoid compounds, diterpene synthase genes for specialized metabolite synthesis were cloned from C. obtusa and C. obtusa var. formosana. Using an Escherichia coli co-expression system, eight diterpene synthases (diTPSs) were characterized. CoCPS and CovfCPS are class II monofunctional (+)-copalyl diphosphate synthases [(+)-CPSs]. Class I monofunctional CoLS and CovfLS convert (+)-copalyl diphosphate [(+)-CPP] to levopimaradiene, CoBRS, CovfBRS1, and CovfBRS3 convert (+)-CPP to (-)-beyerene, and CovfSDS converts (+)-CPP to (-)-sandaracopimaradiene. These enzymes are all monofunctional diterpene syntheses in Cupressaceae family of gymnosperm, and differ from those in Pinaceae. The discovery of the enzyme responsible for the biosynthesis of tetracyclic diterpene (-)-beyerene was characterized for the first time. Diterpene synthases with different catalytic functions exist in closely related species within the Cupressaceae family, indicating that this group of monofunctional diterpene synthases is particularly prone to the evolution of new functions and development of species-specific specialized diterpenoid constituents.

Biosynthesis and the Transcriptional Regulation of Terpenoids in Tea Plants (Camellia sinensis)

Terpenes, especially volatile terpenes, are important components of tea aroma due to their unique scents. They are also widely used in the cosmetic and medical industries. In addition, terpene emission can be induced by herbivory, wounding, light, low temperature, and other stress conditions, leading to plant defense responses and plant-plant interactions. The transcriptional levels of important core genes (including HMGR, DXS, and TPS) involved in terpenoid biosynthesis are up- or downregulated by the MYB, MYC, NAC, ERF, WRKY, and bHLH transcription factors. These regulators can bind to corresponding cis-elements in the promoter regions of the corresponding genes, and some of them interact with other transcription factors to form a complex. Recently, several key terpene synthesis genes and important transcription factors involved in terpene biosynthesis have been isolated and functionally identified from tea plants. In this work, we focus on the research progress on the transcriptional regulation of terpenes in tea plants (Camellia sinensis) and thoroughly detail the biosynthesis of terpene compounds, the terpene biosynthesis-related genes, the transcription factors involved in terpene biosynthesis, and their importance. Furthermore, we review the potential strategies used in studying the specific transcriptional regulation functions of candidate transcription factors that have been discriminated to date.

Transcriptome and metabolome analysis of stress tolerance to aluminium in Vitis quinquangularis

Transcriptional and metabolic regulation of aluminium tolerance of Chinese wild Vitis quinquangularis after Al treatment for 12 h: genes and pathways related to stress resistance are activated to cope with Al stress. The phytotoxicity of aluminium (Al) has become a major issue in inhibiting plant growth in acidic soils. Chinese wild Vitis species have excellent stress resistance. In this study, to explore the mechanism underlying Al tolerance in Chinese wild Vitis quinquangularis, we conducted a transcriptome analysis to understand the changes in gene expression and pathways in V. quinquangularis leaves after Al treatment for 12 h (Al_12 h). Compared with the control (CK) treatment, 2266 upregulated differentially expressed genes (DEGs) and 2943 downregulated DEGs were identified after Al treatment. We analysed the top 60 upregulated DEGs and found that these genes were related mostly to cell wall organization or biogenesis, transition metal ion binding, etc. Another analysis of all the upregulated DEGs showed that genes related to the ABC transport pathway, salicylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA) hormone signalling pathway were expressed. Transcriptome and metabolome analysis revealed that genes and metabolites (phenylalanine, cinnamate and quercetin) related to the phenylalanine metabolic pathway were expressed. In summary, the results provide a new contribution to a better understanding of the metabolic changes that occur in grapes after Al stress as well as to research on improving the resistance of grape cultivars.

Discovery and characterization of diterpene synthases in Chamaecyparis formosensis Matsum. which participated in an unprecedented diterpenoid biosynthesis route in conifer

Chamaecyparis formosensis Matsum. is an endemic and precious coniferous species of Taiwan, and is known for a high abundance of specialized metabolites, which contributes to the excellent timber durability. Several terpenoids were identified and isolated from C. formosensis wood and needles, and exhibit anti-fungal and anti-bacterial bioactivities, which may participate in plant defense against pathogens. In various identified compounds, not only cadinene and ferruginol, were identified in C. formosensis extracts but also unique diterpenoids, which include pisferal, totarol, and derivates of isoabienol. To understand the biosynthesis of these specific diterpenoids, we conducted a series of functional characterization of the C. formosensis diterpene synthases (CfdiTPSs), which participate in skeleton formation and differentiation of diterpenes. In this study, we identified eight diTPSs from C. formosensis transcriptome, and they all contain either class I or class II motif, which indicates they are all monofunctional enzymes. These candidates consist of three class II diTPSs and five class I diTPSs, and after conducting in vivo and in vitro assays, class II diTPS CfCPS1 was characterized as a (+)-copalyl diphosphate synthase ((+)-CPS), and class I diTPSs CfKSL1 could further convert (+)-copalyl diphosphate ((+)-CPP) to levopimaradiene. Meanwhile, CfKSL1 also accepted labda-13-en-8-ol diphosphate (LPP) as substrate and formed monoyl oxide. Another class I diTPS, CfKSL4, exhibits a strong enzymatic ability of isoabienol synthase, which is firstly reported in conifer. This finding provides potential participants in the biosynthesis of unique diterpenoids, and with this knowledge, we can further expand our understanding of diterpenoid metabolism in Cupressaceae and their potential role in plant defense.