Additional diterpenes from Physcomitrella patens synthesized by copalyl diphosphate/kaurene synthase (PpCPS/KS)

Overexpression of Physcomitrium patens cell cycle regulators leads to larger gametophytes

Regulation of cell division is crucial for the development of multicellular organisms, and in plants, this is in part regulated by the D-type cyclins (CYCD) and cyclin-dependent kinase A (CDKA) complex. Cell division regulation in Physcomitrium differs from other plants, by having cell division checks at both the G1 to S and G2 to M transition, controlled by the CYCD1/CDKA2 and CYCD2/CDKA1 complexes, respectively. This led us to hypothesize that upregulation of cell division could be archived in Bryophytes, without the devastating phenotypes observed in Arabidopsis. Overexpressing lines of PpCYCD1, PpCYCD2, PpCDKA1, or PpCDKA2 under Ubiquitin promotor control provided transcriptomic and phenotypical data that confirmed their involvement in the G1 to S or G2 to M transition control. Interestingly, combinatorial overexpression of all four genes produced plants with dominant PpCDKA2 and PpCYCD1 phenotypes and led to plants with twice as large gametophores. No detrimental phenotypes were observed in this line and two of the major carbon sinks in plants, the cell wall and starch, were unaffected by the increased growth rate. These results show that the cell cycle characteristics of P. patens can be manipulated by the ectopic expression of cell cycle regulators.

Divergent Evolution of the Diterpene Biosynthesis Pathway in Tea Plants (Camellia sinensis) Caused by Single Amino Acid Variation of ent-Kaurene Synthase

Most plant terpenoids are classified as secondary metabolites. A small portion of them are products of primary metabolism biosynthesized by relatively conserved pathways. Gibberellins (GAs), which are essential for plant growth and development, are diterpenoid phytohormones. (E,E,E)-Geranylgeranyl diphosphate (GGPP) is the precursor for both GAs and other diterpenoids of secondary metabolism. ent-Kaurene biosynthesis from GGPP is a key step of GA formation, which is catalyzed by two sequential and dedicated diterpene synthases (diTPSs): ent-copalyl diphosphate synthase (CPS) and ent-kaurene synthase (KS) of the terpene synthase gene family. Sharing a common evolutionary origin, CPS and KS belong to different TPS subfamilies. Tea plant (Camellia sinensis), the subject of this study, is a leaf-based economic crop. Budbreak mainly manipulated by GAs is a primary factor for targeted tea breeding. The key genes for gibberellin biosynthesis are known; however, they have not yet been characterized in tea plants. Here, we identified and functionally characterized three diterpene biosynthesis-related genes, including one CPS and two highly similar KSs in tea plants. These genes were initially identified through transcriptome sequencing. The functional characterization determined by enzymatic activity assay indicated that CsCPS could catalyze GGPP to form ent-copalyl diphosphate (ent-CPP), which was further used as the substrate by CsKS1 to produce ent-kaurene or by CsKS2 to produce 16α-hydroxy-ent-kaurane with ent-kaurene as a minor product, respectively. We demonstrated that the divergent evolution of diterpene biosynthesis in tea plants resulted from gene duplication of KSs, followed by functional divergence caused by single amino acid variation. This study would provide an insight into the diterpenoid metabolism and GA biosynthesis in tea plants to further understand leaf bud development or insect resistance and to provide a genetic basis for tea plant breeding.

A Comprehensive Survey on the Terpene Synthase Gene Family Provides New Insight into Its Evolutionary Patterns

Terpenes are organic compounds and play important roles in plant growth and development as well as in mediating interactions of plants with the environment. Terpene synthases (TPSs) are the key enzymes responsible for the biosynthesis of terpenes. Although some species were employed for the genome-wide identification and characterization of the TPS family, limited information is available regarding the evolution, expansion, and retention mechanisms occurring in this gene family. We performed a genome-wide identification of the TPS family members in 50 sequenced genomes. Additionally, we also characterized the TPS family from aromatic spearmint and basil plants using RNA-Seq data. No TPSs were identified in algae genomes but the remaining plant species encoded various numbers of the family members ranging from 2 to 79 full-length TPSs. Some species showed lineage-specific expansion of certain subfamilies, which might have contributed toward species or ecotype divergence or environmental adaptation. A large-scale family expansion was observed mainly in dicot and monocot plants, which was accompanied by frequent domain loss. Both tandem and segmental duplication significantly contributed toward family expansion and expression divergence and played important roles in the survival of these expanded genes. Our data provide new insight into the TPS family expansion and evolution and suggest that TPSs might have originated from isoprenyl diphosphate synthase genes.

Insights into Heterologous Biosynthesis of Arteannuin B and Artemisinin in Physcomitrella patens

: Metabolic engineering is an integrated bioengineering approach, which has made considerable progress in producing terpenoids in plants and fermentable hosts. Here, the full biosynthetic pathway of artemisinin, originating from Artemisia annua, was integrated into the moss Physcomitrella patens. Different combinations of the five artemisinin biosynthesis genes were ectopically expressed in P. patens to study biosynthesis pathway activity, but also to ensure survival of successful transformants. Transformation of the first pathway gene, ADS, into P. patens resulted in the accumulation of the expected metabolite, amorpha-4,11-diene, and also accumulation of a second product, arteannuin B. This demonstrates the presence of endogenous promiscuous enzyme activity, possibly cytochrome P450s, in P. patens. Introduction of three pathway genes, ADS-CYP71AV1-ADH1 or ADS-DBR2-ALDH1 both led to the accumulation of artemisinin, hinting at the presence of one or more endogenous enzymes in P. patens that can complement the partial pathways to full pathway activity. Transgenic P. patens lines containing the different gene combinations produce artemisinin in varying amounts. The pathway gene expression in the transgenic moss lines correlates well with the chemical profile of pathway products. Moreover, expression of the pathway genes resulted in lipid body formation in all transgenic moss lines, suggesting that these may have a function in sequestration of heterologous metabolites. This work thus provides novel insights into the metabolic response of P. patens and its complementation potential for A. annua artemisinin pathway genes. Identification of the related endogenous P. patens genes could contribute to a further successful metabolic engineering of artemisinin biosynthesis, as well as bioengineering of other high-value terpenoids in P. patens.

Cytochrome P450 enzymes: A driving force of plant diterpene diversity

In plant terpene biosynthesis, oxidation of the hydrocarbon backbone produced by terpene synthases is typically carried out by cytochrome P450 oxygenases (CYPs). The modifications introduced by CYPs include hydroxylations, sequential oxidations at one position and ring rearrangements and closures. These reactions significantly expand the structural diversity of terpenoids, but also provide anchoring points for further decorations by various transferases. In recent years, there has been a significant increase in reports of CYPs involved in plant terpene pathways. Plant diterpenes represent an important class of metabolites that includes hormones and a number of industrially relevant compounds such as pharmaceutical, aroma or food ingredients. In this review, we provide a comprehensive survey on CYPs reported to be involved in plant diterpene biosynthesis to date. A phylogenetic analysis showed that only few CYP clans are represented in diterpene biosynthesis, namely CYP71, CYP85 and CYP72. Remarkably few CYP families and subfamilies within those clans are involved, indicating specific expansion of these clades in plant diterpene biosynthesis. Nonetheless, the evolutionary trajectory of CYPs of specialized diterpene biosynthesis is diverse. Some are recently derived from gibberellin biosynthesis, while others have a more ancient history with recent expansions in specific plant families. Among diterpenoids, labdane-related diterpenoids represent a dominant class. The availability of CYPs from diverse plant species able to catalyze oxidations in specific regions of the labdane-related backbones provides opportunities for combinatorial biosynthesis to produce novel diterpene compounds that can be screened for biological activities of interest.

A database-driven approach identifies additional diterpene synthase activities in the mint family (Lamiaceae)

Members of the mint family (Lamiaceae) accumulate a wide variety of industrially and medicinally relevant diterpenes. We recently sequenced leaf transcriptomes from 48 phylogenetically diverse Lamiaceae species. Here, we summarize the available chemotaxonomic and enzyme activity data for diterpene synthases (diTPSs) in the Lamiaceae and leverage the new transcriptomes to explore the diTPS sequence and functional space. Candidate genes were selected with an intent to evenly sample the sequence homology space and to focus on species in which diTPS transcripts were found, yet from which no diterpene structures have been previously reported. We functionally characterized nine class II diTPSs and 10 class I diTPSs from 11 distinct plant species and found five class II activities, including two novel activities, as well as a spectrum of class I activities. Among the class II diTPSs, we identified a neo-cleroda-4(18),13E-dienyl diphosphate synthase from Ajuga reptans, catalyzing the likely first step in the biosynthesis of a variety of insect-antifeedant compounds. Among the class I diTPSs was a palustradiene synthase from Origanum majorana, leading to the discovery of specialized diterpenes in that species. Our results provide insights into the diversification of diterpene biosynthesis in the mint family and establish a comprehensive foundation for continued investigation of diterpene biosynthesis in the Lamiaceae.

Engineering modular diterpene biosynthetic pathways in Physcomitrella patens

Modular assembly and heterologous expression in the moss Physcomitrella patens of pairs of diterpene synthases results in accumulation of modern land plant diterpenoids. Physcomitrella patens is a representative of the ancient bryophyte plant lineage with a genome size of 511 Mb, dominant haploid life cycle and limited chemical and metabolic complexity. For these plants, exceptional capacity for genome editing through homologous recombination is met with recently demonstrated in vivo assembly of multiple heterologous DNA fragments. These traits earlier made P. patens an attractive choice as a biotechnological chassis for photosynthesis-driven production of recombinant peptides. The lack of diterpene gibberellic acid phytohormones in P. patens combined with the recent targeted disruption of the single bifunctional diterpene synthase yielded lines devoid of endogenous diterpenoid metabolites and well-suited for engineering of terpenoid production. Here, we mimicked the modular nature of diterpene biosynthetic pathways found in modern land plants by developing a flexible pipeline to install three combinations of class II and class I diterpene synthases in P. patens to access industrially relevant diterpene biomaterials. In addition to a well-established neutral locus for targeted integration, we also explored loci created by a class of Long Terminal Repeat Retrotransposon present at moderate number in the genome of P. patens. Assembly of the pathways and production of the enzymes from the neutral locus led to accumulation of diterpenes matching the reported activities in the angiosperm sources. In contrast, insights gained with the retrotransposon loci indicate their suitability for targeting, but reveal potentially inherent complications which may require adaptation of the experimental design.

Two residues determine the product profile of the class II diterpene synthases TPS14 and TPS21 of Tripterygium wilfordii

The medicinal plant Tripterygium wilfordii (Celastraceae) contains a pair of class II diterpene synthases (diTPS) of specialized labdane-type metabolism that, despite remarkably close homology, form strikingly different products. TwTPS21 catalyzes bicyclization of the linear C20 precursor geranylgeranyl diphosphate to ent-copal-8-ol diphosphate, while TwTPS14 forms kolavenyl diphosphate. To determine the amino acid signature controlling the functional divergence of the homologues, we modeled their structures based on an existing crystal structure of the Arabidopsis ent-copalyl diphosphate synthase, archetypal of diTPSs in general metabolism of gibberellin phytohormones. Of the residues differing between TwTPS21 and TwTPS14 two located to the predicted active site, and we hypothesized that these are responsible for the functional differentiation of the enzymes. Using site-directed mutagenesis, we generated a panel of six variants, where one, or both positions were exchanged between the enzymes. In coupled heterologous assays with a corresponding class I diTPS, TwTPS2, complete product interchange was observed in variants with both reciprocal mutations, while substitutions of either residue gave mixed product profiles. Two mutants, TwTPS14:Y265H and TwTPS21:A325V, also produced ent-copalyl diphosphate, highlighting the evolutionary potential of enzymes of this family to drive rapid diversification of plant diterpene biosynthesis through neo-functionalization. Our study contributes to the understanding of structure-function relation in plant class II diTPSs and complements previous mutational studies of Arabidopsis ent-copalyl diphosphate synthase with additional examples from the specialized metabolism of T. wilfordii.

The terpene synthase gene family in Tripterygium wilfordii harbors a labdane-type diterpene synthase among the monoterpene synthase TPS-b subfamily

Tripterygium wilfordii (Celastraceae) is a medicinal plant with anti-inflammatory and immunosuppressive properties. Identification of a vast array of unusual sesquiterpenoids, diterpenoids and triterpenoids in T. wilfordii has spurred investigations of their pharmacological properties. The tri-epoxide lactone triptolide was the first of many diterpenoids identified, attracting interest due to the spectrum of bioactivities. To probe the genetic underpinning of diterpenoid diversity, an expansion of the class II diterpene synthase (diTPS) family was recently identified in a leaf transcriptome. Following detection of triptolide and simple diterpene scaffolds in the root, we sequenced and mined the root transcriptome. This allowed identification of the root-specific complement of TPSs and an expansion in the class I diTPS family. Functional characterization of the class II diTPSs established their activities in the formation of four C-20 diphosphate intermediates, precursors of both generalized and specialized metabolism and a novel scaffold for Celastraceae. Functional pairs of the class I and II enzymes resulted in formation of three scaffolds, accounting for some of the terpenoid diversity found in T. wilfordii. The absence of activity-forming abietane-type diterpenes encouraged further testing of TPSs outside the canonical class I diTPS family. TwTPS27, close relative of mono-TPSs, was found to couple with TwTPS9, converting normal-copalyl diphosphate to miltiradiene. The phylogenetic distance to established diTPSs indicates neo-functionalization of TwTPS27 into a diTPS, a function not previously observed in the TPS-b subfamily. This example of evolutionary convergence expands the functionality of TPSs in the TPS-b family and may contribute miltiradiene to the diterpenoids of T. wilfordii.

The decision to germinate is regulated by divergent molecular networks in spores and seeds

Dispersal is a key step in land plant life cycles, usually via formation of spores or seeds. Regulation of spore- or seed-germination allows control over the timing of transition from one generation to the next, enabling plant dispersal. A combination of environmental and genetic factors determines when seed germination occurs. Endogenous hormones mediate this decision in response to the environment. Less is known about how spore germination is controlled in earlier-evolving nonseed plants. Here, we present an in-depth analysis of the environmental and hormonal regulation of spore germination in the model bryophyte Physcomitrella patens (Aphanoregma patens). Our data suggest that the environmental signals regulating germination are conserved, but also that downstream hormone integration pathways mediating these responses in seeds were acquired after the evolution of the bryophyte lineage. Moreover, the role of abscisic acid and diterpenes (gibberellins) in germination assumed much greater importance as land plant evolution progressed. We conclude that the endogenous hormone signalling networks mediating germination in response to the environment may have evolved independently in spores and seeds. This paves the way for future research about how the mechanisms of plant dispersal on land evolved.

Extending the biosynthetic repertoires of cyanobacteria and chloroplasts

Chloroplasts in plants and algae and photosynthetic microorganisms such as cyanobacteria are emerging hosts for sustainable production of valuable biochemicals, using only inorganic nutrients, water, CO2 and light as inputs. In the past decade, many bioengineering efforts have focused on metabolic engineering and synthetic biology in the chloroplast or in cyanobacteria for the production of fuels, chemicals and complex, high-value bioactive molecules. Biosynthesis of all these compounds can be performed in photosynthetic organelles/organisms by heterologous expression of the appropriate pathways, but this requires optimization of carbon flux and reducing power, and a thorough understanding of regulatory pathways. Secretion or storage of the compounds produced can be exploited for the isolation or confinement of the desired compounds. In this review, we explore the use of chloroplasts and cyanobacteria as biosynthetic compartments and hosts, and we estimate the levels of production to be expected from photosynthetic hosts in light of the fraction of electrons and carbon that can potentially be diverted from photosynthesis. The supply of reducing power, in the form of electrons derived from the photosynthetic light reactions, appears to be non-limiting, but redirection of the fixed carbon via precursor molecules presents a challenge. We also discuss the available synthetic biology tools and the need to expand the molecular toolbox to facilitate cellular reprogramming for increased production yields in both cyanobacteria and chloroplasts.

Therapeutic Potential of Essential Oils Focusing on Diterpenes

Among all plant derivates, essential oils (EOs) have gained the attention of many scientists. Diterpenes, a family of components present in some EO, are becoming a milestone in the EOs world. The goal of this review is to describe a scenario of diterpenes taking into health-consumption deportment. Previous studies revealed that diterpenes have antioxidant, antimicrobial, antiviral, antiprotozoal, cytotoxic, anticancer, antigenotoxic, antimutagenic, chemopreventive, antiinflammatory, antinociceptive, immunostimulatory, organoprotective, antidiabetic, lipid-lowering, antiallergic, antiplatelet, antithrombotic, and antitoxin activities. In conclusion, diterpenes may be an immense featuring concern in pharmaceutical consumption from a drug discovery point of view. Copyright © 2016 John Wiley & Sons, Ltd.

In vivo assembly of DNA-fragments in the moss, Physcomitrella patens

Direct assembly of multiple linear DNA fragments via homologous recombination, a phenomenon known as in vivo assembly or transformation associated recombination, is used in biotechnology to assemble DNA constructs ranging in size from a few kilobases to full synthetic microbial genomes. It has also enabled the complete replacement of eukaryotic chromosomes with heterologous DNA. The moss Physcomitrella patens, a non-vascular and spore producing land plant (Bryophyte), has a well-established capacity for homologous recombination. Here, we demonstrate the in vivo assembly of multiple DNA fragments in P. patens with three examples of effective genome editing: we (i) efficiently deleted a genomic locus for diterpenoid metabolism yielding a biosynthetic knockout, (ii) introduced a salt inducible promoter, and (iii) re-routed endogenous metabolism into the formation of amorphadiene, a precursor of high-value therapeutics. These proof-of-principle experiments pave the way for more complex and increasingly flexible approaches for large-scale metabolic engineering in plant biotechnology.