The eukaryotic MEP-pathway genes are evolutionarily conserved and originated from Chlaymidia and cyanobacteria

Functional Identification and Regulatory Active Site Screening of the DfDXS Gene of Dryopteris fragrans

Dryopteris fragrans (L.) Schott has anti-inflammatory and antioxidant properties, and terpenoids are important components of its active constituents. The methyl-D-erythritol 4-phosphate (MEP) pathway is one of the major pathways for the synthesis of terpene precursors in plants, and 1-deoxy-D-xylulose-5-phosphate synthase (DXS) is the first rate-limiting enzyme in this pathway. DXS has been shown to be associated with increased stress tolerance in plants. In this experiment, two DXS genes were extracted from the D. fragrans transcriptome and named DfDXS1 and DfDXS2. Based on phylogenetic tree and conserved motif analyses, DXS was shown to be highly conserved evolutionarily and its localization to chloroplasts was determined by subcellular localization. Prokaryotic expression results showed that the number and growth status of recombinant colonies were better than the control under 400 mM NaCl salt stress and 800 mM mannitol-simulated drought stress. In addition, the DfDXS1 and DfDXS2 transgenic tobacco plants showed improved resistance to drought and salt stress. DfDXS1 and DfDXS2 responded strongly to methyl jasmonate (MeJA) and PEG-mimicked drought stress following exogenous hormone and abiotic stress treatments of D. fragrans. The transcriptional active sites were investigated by dual luciferase and GUS staining assays, and the results showed that the STRE element (AGGGG), the ABRE element (ACGTGGC), and the MYC element (CATTTG) were the important transcriptional active sites in the promoters of the two DXS genes, which were closely associated with hormone response and abiotic stress. These results suggest that the DfDXS gene of D. fragrans plays an important role in hormone signaling and response to stress. This study provides a reference for analyzing the molecular mechanisms of stress tolerance in D. fragrans.

Impact of tps1 Deletion and Overexpression on Terpene Metabolites in Trichoderma atroviride

Terpenoids are structurally diverse natural products that have been widely used in the pharmaceutical, food, and cosmetic industries. Research has shown that fungi produce a variety of terpenoids, yet fungal terpene synthases remain not thoroughly explored. In this study, the tps1 gene, a crucial component of the terpene synthetic pathway, was isolated from Trichoderma atroviride HB20111 through genome mining. The function of this gene in the terpene synthetic pathway was investigated by constructing tps1-gene-deletion- and overexpression-engineered strains and evaluating the expression differences in the tps1 gene at the transcript level. HS-SPME-GC-MS analysis revealed significant variations in terpene metabolites among wild-type, tps1-deleted (Δtps1), and tps1-overexpressed (Otps1) strains; for instance, most sesquiterpene volatile organic compounds (VOCs) were notably reduced or absent in the Δtps1 strain, while nerolidol, β-acorenol, and guaiene were particularly produced by the Otps1 strain. However, both the Δtps1 and Otps1 strains produced new terpene metabolites compared to the wild-type, which indicated that the tps1 gene played an important role in terpene synthesis but was not the only gene involved in T. atroviride HB20111. The TPS1 protein encoded by the tps1 gene could function as a sesquiterpene cyclase through biological information and evolutionary tree analysis. Additionally, fungal inhibition assay and wheat growth promotion assay results suggested that the deletion or overexpression of the tps1 gene had a minimal impact on fungal inhibitory activity, plant growth promotion, and development, as well as stress response. This implies that these activities of T. atroviride HB20111 might result from a combination of multiple metabolites rather than being solely dependent on one specific metabolite. This study offers theoretical guidance for future investigations into the mechanism of terpenoid synthesis and serves as a foundation for related studies on terpenoid metabolic pathways in fungi.

Genomic analysis based on chromosome-level genome assembly reveals Myrtaceae evolution and terpene biosynthesis of rose myrtle

BACKGROUND

Rose myrtle (Rhodomyrtus tomentosa (Ait.) Hassk), is an evergreen shrub species belonging to the family Myrtaceae, which is enriched with bioactive volatiles (α-pinene and β-caryophyllene) with medicinal and industrial applications. However, the mechanism underlying the volatile accumulation in the rose myrtle is still unclear.

RESULTS

Here, we present a chromosome-level genomic assembly of rose myrtle (genome size = 466 Mb, scaffold N50 = 43.7 Mb) with 35,554 protein-coding genes predicted. Through comparative genomic analysis, we found that gene expansion and duplication had a potential contribution to the accumulation of volatile substances. We proposed that the action of positive selection was significantly involved in volatile accumulation. We identified 43 TPS genes in R. tomentosa. Further transcriptomic and TPS gene family analyses demonstrated that the distinct gene subgroups of TPS may contribute greatly to the biosynthesis and accumulation of different volatiles in the Myrtle family of shrubs and trees. The results suggested that the diversity of TPS-a subgroups led to the accumulation of special sesquiterpenes in different plants of the Myrtaceae family.

CONCLUSIONS

The high quality chromosome-level rose myrtle genome and the comparative analysis of TPS gene family open new avenues for obtaining a higher commercial value of essential oils in medical plants.

Activation of stress-response genes by retrograde signaling-mediated destabilization of nuclear importin IMPα-9 and its interactor TPR2

Stress-induced retrograde signal transmission from the plastids to the nucleus has long puzzled plant biologists. To address this, we performed a suppressor screen of the ceh1 mutant, which contains elevated 2-C-methyl-d-erythritol-2,4-cyclopyrophosphate (MEcPP) levels, and identified the gain-of-function mutant impα-9, which shows reversed dwarfism and suppressed expression of stress-response genes in the ceh1 background despite heightened MEcPP. Subsequent genetic and biochemical analyses established that the accumulation of MEcPP initiates an upsurge in Arabidopsis SKP1-like 1 (ASK1) abundance, a pivotal component in the proteasome degradation pathway. This increase in ASK1 prompts the degradation of IMPα-9. Moreover, we uncovered a protein-protein interaction between IMPα-9 and TPR2, a transcriptional co-suppressor and found that a reduction in IMPα-9 levels coincides with a decrease in TPR2 abundance. Significantly, the interaction between IMPα-9 and TPR2 was disrupted in impα-9 mutants, highlighting the critical role of a single amino acid alteration in maintaining their association. Disruption of their interaction results in the reversal of MEcPP-associated phenotypes. Chromatin immunoprecipitation coupled with sequencing analyses revealed that TPR2 binds globally to stress-response genes and suggested that IMPα-9 associates with the chromatin. They function together to suppress the expression of stress-response genes under normal conditions, but this suppression is alleviated in response to stress through the degradation of the suppressing machinery. The biological relevance of our discoveries was validated under high light stress, marked by MEcPP accumulation, elevated ASK1 levels, IMPα-9 degredation, reduced TPR2 abundance, and subsequent activation of a network of stress-response genes. In summary, our study collectively unveils fresh insights into plant adaptive mechanisms, highlighting intricate interactions among retrograde signaling, the proteasome, and nuclear transport machinery.

Expanded Archaeal Genomes Shed New Light on the Evolution of Isoprenoid Biosynthesis

Isoprenoids and their derivatives, essential for all cellular life on Earth, are particularly crucial in archaeal membrane lipids, suggesting that their biosynthesis pathways have ancient origins and play pivotal roles in the evolution of early life. Despite all eukaryotes, archaea, and a few bacterial lineages being known to exclusively use the mevalonate (MVA) pathway to synthesize isoprenoids, the origin and evolutionary trajectory of the MVA pathway remain controversial. Here, we conducted a thorough comparison and phylogenetic analysis of key enzymes across the four types of MVA pathway, with the particular inclusion of metagenome assembled genomes (MAGs) from uncultivated archaea. Our findings support an archaeal origin of the MVA pathway, likely postdating the divergence of Bacteria and Archaea from the Last Universal Common Ancestor (LUCA), thus implying the LUCA's enzymatic inability for isoprenoid biosynthesis. Notably, the Asgard archaea are implicated in playing central roles in the evolution of the MVA pathway, serving not only as putative ancestors of the eukaryote- and Thermoplasma-type routes, but also as crucial mediators in the gene transfer to eukaryotes, possibly during eukaryogenesis. Overall, this study advances our understanding of the origin and evolutionary history of the MVA pathway, providing unique insights into the lipid divide and the evolution of early life.

RNA-seq analysis reveals narrow differential gene expression in MEP and MVA pathways responsible for phytochemical divergence in extreme genotypes of Thymus daenensis Celak

BACKGROUND

Here, we investigated the underlying transcriptional-level evidence behind phytochemical differences between two metabolically extreme genotypes of Thymus daenensis. The genotypes 'Zagheh-11' (thymol/carvacrol type, poor in essential oil [EO] [2.9%] but rich in triterpenic acids) and 'Malayer-21' (thymol type and rich in EO [3.8%]) were selected from an ongoing breeding program and then clonally propagated for further experimental use.

MATERIALS AND METHODS

GC-MS, GC-FID, and HPLC-PDA were utilized to monitor the fluctuation of secondary metabolites at four phenological stages (vegetative, bud burst, early, and full-flowering stages). The highest phytochemical divergence was observed at early flowering stage. Both genotypes were subjected to mRNA sequencing (approximately 100 million paired reads) at the aforementioned stage. The expression patterns of four key genes involved in the biosynthesis of terpenoids were also validated using qRT-PCR.

RESULTS

Carvacrol content in 'Zagheh-11' (26.13%) was approximately 23 times higher than 'Malayer-21' (1.12%). Reciprocally, about 10% higher thymol was found in 'Malayer-21' (62.15%). Moreover, the concentrations of three major triterpenic acids in 'Zagheh-11' were approximately as twice as those found in 'Malayer-21'. Transcriptome analysis revealed a total of 1840 unigenes that were differentially expressed, including terpene synthases, cytochrome P450, and terpenoid backbone genes. Several differentially expressed transcription factors (such as MYB, bZIP, HB-HD-ZIP, and WRKY families) were also identified. These results suggest that an active cytosolic mevalonate (MVA) pathway may be linked to higher levels of sesquiterpenes, triterpenic acids, and carvacrol in 'Zagheh-11'. The chloroplastic pathway of methyl erythritol phosphate (MEP) may have also contributed to a higher accumulation of thymol in Malayer-21. Indeed, 'Zagheh-11' showed higher expression of certain genes (HMGR, CYP71D180, β-amyrin 28-monooxygenase, and sesquiterpene synthases) in the MVA pathway, while some genes in the MEP pathway (including DXR, ispG, and γ-terpinene synthase) were distinctly expressed in Malayer-21. Future efforts in metabolic engineering of MVA/MEP pathways may benefit from these findings to produce increased levels of desired secondary metabolites at commercial scale.

Genomic characterization of WRKY transcription factors related to secoiridoid biosynthesis in Gentiana macrophylla

Gentiana macrophylla is one of Chinese herbal medicines in which 4 kinds of iridoids or secoiridoids, such as loganic acid, sweroside, swertiamarin, and gentiopicroside, are identified as the dominant medicinal secondary metabolites. WRKY, as a large family of transcription factors (TFs), plays an important role in the synthesis of secondary metabolites in plants. Therefore, WRKY genes involved in the biosynthesis of secoiridoids in G. macrophylla were systematically studied. First, a comprehensive genome-wide analysis was performed, and 42 GmWRKY genes were identified, which were unevenly distributed in 12 chromosomes. Accordingly, gene structure, collinearity, sequence alignment, phylogenetic, conserved motif and promoter analyses were performed, and the GmWRKY proteins were divided into three subfamilies based on phylogenetic and multiple sequence alignment analyses. Moreover, the enzyme-encoding genes of the secoiridoid biosynthesis pathway and their promoters were then analysed, and the contents of the four secoiridoids were determined in different tissues. Accordingly, correlation analysis was performed using Pearson's correlation coefficient to construct WRKY gene-enzyme-encoding genes and WRKY gene-metabolite networks. Meanwhile, G. macrophylla seedlings were treated with methyl jasmonate (MeJA) to detect the dynamic change trend of GmWRKYs, biosynthetic genes, and medicinal ingredient accumulation. Thus, a total of 12 GmWRKYs were identified to be involved in the biosynthesis of secoiridoids, of which 8 (GmWRKY1, 6, 12, 17, 33, 34, 38 and 39) were found to regulate the synthesis of gentiopicroside, and 4 (GmWRKY7, 14, 26 and 41) were found to regulate the synthesis of loganic acid. Taken together, this study systematically identified WRKY transcription factors related to the biosynthesis of secoiridoids in G. macrophylla, which could be used as a cue for further investigation of WRKY gene functions in secondary metabolite accumulation.

Quantifying Global Origin-Diagnostic Features and Patterns in Biotic and Abiotic Acyclic Lipids for Life Detection

Lipids are a geologically robust class of organics ubiquitous to life as we know it. Lipid-like soluble organics are synthesized abiotically and have been identified in carbonaceous meteorites and on Mars. Ascertaining the origin of lipids on Mars would be a profound astrobiological achievement. We enumerate origin-diagnostic features and patterns in two acyclic lipid classes, fatty acids (i.e., carboxylic acids) and acyclic hydrocarbons, by collecting and analyzing molecular data reported in over 1500 samples from previously published studies of terrestrial and meteoritic organics. We identify 27 combined (15 for fatty acids, 12 for acyclic hydrocarbons) molecular patterns and structural features that can aid in distinguishing biotic from abiotic synthesis. Principal component analysis (PCA) demonstrates that multivariate analyses of molecular features (16 for fatty acids, 14 for acyclic hydrocarbons) can potentially indicate sample origin. Terrestrial lipids are dominated by longer straight-chain molecules (C4-C34 fatty acids, C14-C46 acyclic hydrocarbons), with predominance for specific branched and unsaturated isomers. Lipid-like meteoritic soluble organics are shorter, with random configurations. Organic solvent-extraction techniques are most commonly reported, motivating the design of our novel instrument, the Extractor for Chemical Analysis of Lipid Biomarkers in Regolith (ExCALiBR), which extracts lipids while preserving origin-diagnostic features that can indicate biogenicity.

Evolutionary flexibility and rigidity in the bacterial methylerythritol phosphate (MEP) pathway

Terpenoids are a diverse class of compounds with wide-ranging uses including as industrial solvents, pharmaceuticals, and fragrances. Efforts to produce terpenoids sustainably by engineering microbes for fermentation are ongoing, but industrial production still largely relies on nonrenewable sources. The methylerythritol phosphate (MEP) pathway generates terpenoid precursor molecules and includes the enzyme Dxs and two iron-sulfur cluster enzymes: IspG and IspH. IspG and IspH are rate limiting-enzymes of the MEP pathway but are challenging for metabolic engineering because they require iron-sulfur cluster biogenesis and an ongoing supply of reducing equivalents to function. Therefore, identifying novel alternatives to IspG and IspH has been an on-going effort to aid in metabolic engineering of terpenoid biosynthesis. We report here an analysis of the evolutionary diversity of terpenoid biosynthesis strategies as a resource for exploration of alternative terpenoid biosynthesis pathways. Using comparative genomics, we surveyed a database of 4,400 diverse bacterial species and found that some may have evolved alternatives to the first enzyme in the pathway, Dxs making it evolutionarily flexible. In contrast, we found that IspG and IspH are evolutionarily rigid because we could not identify any species that appear to have enzymatic routes that circumvent these enzymes. The ever-growing repository of sequenced bacterial genomes has great potential to provide metabolic engineers with alternative metabolic pathway solutions. With the current state of knowledge, we found that enzymes IspG and IspH are evolutionarily indispensable which informs both metabolic engineering efforts and our understanding of the evolution of terpenoid biosynthesis pathways.

Induction and metabolomic analysis of hairy roots of Atractylodes lancea

Atractylodes lancea is an important source of traditional Chinese medicines. Sesquiterpenoids are the key active compounds in A. lancea, and their presence determines the quality of the material. Hairy hoot (HR) culture is a potential method to produce medicinally active compounds industrially; however, the induction and metabolic profiling of A. lancea HR have not been reported. We found that optimal induction of A. lancea HR was achieved by Agrobacterium rhizogenes strain C58C1 using the young leaves of tissue culture seedlings in the rooting stage as explants. Ultra-performance liquid chromatography-tandem mass spectrometric analyses of the chemical compositions of HR and normal root (NR) led to the annotation of 1046 metabolites. Over 200 differentially accumulated metabolites were identified, with 41 found to be up-regulated in HR relative to NR and 179 down-regulated in HR. Specifically, atractylodin levels were higher in HR, while the levels of β-eudesmol and hinesol were higher in NR. Metabolic pathway analyses showed a significant difference in metabolites of the shikimate acid pathway between HR and NR. Five A. lancea compounds are potential biomarkers for evaluation of HR and NR quality. This study provides an important reference for the application of HR for the production of medicinally active compounds. KEY POINTS: • We established an efficient protocol for the induction of HR in A. lancea • HR was found to have a significantly higher amount of atractylodin than did NRs • Metabolic pathway analyses showed a significant difference in metabolites of the shikimate acid pathway between HR and NR.

COG-imposed Golgi functional integrity determines the onset of dark-induced senescence

Plant survival depends on dynamic stress-response pathways in changing environments. To uncover pathway components, we screened an ethyl methanesulfonate-mutagenized transgenic line containing a stress-inducible luciferase construct and isolated a constitutive expression mutant. The mutant is the result of an amino acid substitution in the seventh subunit of the hetero-octameric conserved oligomeric Golgi (COG) complex of Arabidopsis thaliana. Complementation studies verified the Golgi localization of cog7, and stress tests established accelerated dark-induced carbon deprivation/senescence of the mutant compared with wild-type plants. Multiomics and biochemical analyses revealed accelerated induction of protein ubiquitination and autophagy, and a counterintuitive increased protein N-glycosylation in senescencing cog7 relative to wild-type. A revertant screen using the overexpressor (FOX)-hunting system established partial, but notable rescue of cog7 phenotypes by COG5 overexpression, and conversely premature senescence in reduced COG5 expressing lines. These findings identify COG-imposed Golgi functional integrity as a main player in ensuring cellular survival under energy-limiting conditions.

Differential roles of Cassia tora 1-deoxy-D-xylulose-5-phosphate synthase and 1-deoxy-D-xylulose-5-phosphate reductoisomerase in trade-off between plant growth and drought tolerance

Due to global climate change, drought is emerging as a major threat to plant growth and agricultural productivity. Abscisic acid (ABA) has been implicated in plant drought tolerance, however, its retarding effects on plant growth cannot be ignored. The reactions catalyzed by 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) proteins are critical steps within the isoprenoid biosynthesis in plants. Here, five DXS (CtDXS1-5) and two DXR (CtDXR1-2) genes were identified from Cassia tora genome. Based on multiple assays including the phylogeny, cis-acting element, expression pattern, and subcellular localization, CtDXS1 and CtDXR1 genes might be potential candidates controlling the isoprenoid biosynthesis. Intriguingly, CtDXS1 transgenic plants resulted in drought tolerance but retardant growth, while CtDXR1 transgenic plants exhibited both enhanced drought tolerance and increased growth. By comparison of β-carotene, chlorophyll, abscisic acid (ABA) and gibberellin 3 (GA3) contents in wild-type and transgenic plants, the absolute contents and (or) altered GA3/ABA levels were suggested to be responsible for the balance between drought tolerance and plant growth. The transcriptome of CtDXR1 transgenic plants suggested that the transcript levels of key genes, such as DXS, 9-cis-epoxycarotenoid dioxygenases (NCED), ent-kaurene synthase (KS) and etc, involved with chlorophyll, β-carotene, ABA and GA3 biosynthesis were induced and their contents increased accordingly. Collectively, the trade-off effect induced by CtDXR1 was associated with redesigning architecture in phytohormone homeostasis and thus was highlighted for future breeding purposes.

Biogenic signals from plastids and their role in chloroplast development

Plant seeds do not contain differentiated chloroplasts. Upon germination, the seedlings thus need to gain photoautotrophy before storage energies are depleted. This requires the coordinated expression of photosynthesis genes encoded in nuclear and plastid genomes. Chloroplast biogenesis needs to be additionally coordinated with the light regulation network that controls seedling development. This coordination is achieved by nucleus to plastid signals called anterograde and plastid to nucleus signals termed retrograde. Retrograde signals sent from plastids during initial chloroplast biogenesis are also called biogenic signals. They have been recognized as highly important for proper chloroplast biogenesis and for seedling development. The molecular nature, transport, targets, and signalling function of biogenic signals are, however, under debate. Several studies disproved the involvement of a number of key components that were at the base of initial models of retrograde signalling. New models now propose major roles for a functional feedback between plastid and cytosolic protein homeostasis in signalling plastid dysfunction as well as the action of dually localized nucleo-plastidic proteins that coordinate chloroplast biogenesis with light-dependent control of seedling development. This review provides a survey of the developments in this research field, summarizes the unsolved questions, highlights several recent advances, and discusses potential new working modes.

Exon skipping in IspE Gene is associated with abnormal chloroplast development in rice albino leaf 4 mutant

The formation of leaf color largely depends on the components of pigment accumulation in plastids, which are involved in chloroplast development and division. Here, we isolated and characterized the rice albino leaf 4 (al4) mutant, which exhibited an albino phenotype and eventually died at the three-leaf stage. The chloroplasts in al4 mutant were severely damaged and unable to form intact thylakoid structure. Further analysis revealed that the candidate gene encodes 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase (IspE), which participates in the methylerythritol phosphate (MEP) pathway of isoprenoid biosynthesis. We further demonstrated that the mutation at the exon-intron junction site cause alternative splicing factors fail to distinguish the origin of the GT-AG intron, leading to exon skipping and producing a truncated OsIspE in the al4 mutant. Notably, disruption of OsIspE led to the reduced expression of chloroplast-associated genes, including chloroplast biosynthetic and translation related genes and photosynthetic associated nuclear genes (PhANGs). In summary, these findings reveal that OsIspE plays a crucial role in chloroplast biogenesis and provides novel insights into the function of CMK during chloroplast development in rice.

A fungal tolerance trait and selective inhibitors proffer HMG-CoA reductase as a herbicide mode-of-action

Decades of intense herbicide use has led to resistance in weeds. Without innovative weed management practices and new herbicidal modes of action, the unabated rise of herbicide resistance will undoubtedly place further stress upon food security. HMGR (3-hydroxy-3-methylglutaryl-coenzyme A reductase) is the rate limiting enzyme of the eukaryotic mevalonate pathway successfully targeted by statins to treat hypercholesterolemia in humans. As HMGR inhibitors have been shown to be herbicidal, HMGR could represent a mode of action target for the development of herbicides. Here, we present the crystal structure of a HMGR from Arabidopsis thaliana (AtHMG1) which exhibits a wider active site than previously determined structures from different species. This plant conserved feature enables the rational design of specific HMGR inhibitors and we develop a tolerance trait through sequence analysis of fungal gene clusters. These results suggest HMGR to be a viable herbicide target modifiable to provide a tolerance trait.

Hairy roots: An untapped potential for production of plant products

While plants are an abundant source of valuable natural products, it is often challenging to produce those products for commercial application. Often organic synthesis is too expensive for a viable commercial product and the biosynthetic pathways are often so complex that transferring them to a microorganism is not trivial or feasible. For plants not suited to agricultural production of natural products, hairy root cultures offer an attractive option for a production platform which offers genetic and biochemical stability, fast growth, and a hormone free culture media. Advances in metabolic engineering and synthetic biology tools to engineer hairy roots along with bioreactor technology is to a point where commercial application of the technology will soon be realized. We discuss different applications of hairy roots. We also use a case study of the advancements in understanding of the terpenoid indole alkaloid pathway in Catharanthus roseus hairy roots to illustrate the advancements and challenges in pathway discovery and in pathway engineering.

Reciprocity between a retrograde signal and a putative metalloprotease reconfigures plastidial metabolic and structural states

Reconfiguration of the plastidial proteome in response to environmental cues is central to tailoring adaptive responses. To define the underlying mechanisms and consequences of these reconfigurations, we performed a suppressor screen, using a mutant (ceh1) accumulating high levels of a plastidial retrograde signaling metabolite, MEcPP. We isolated a revertant partially suppressing the dwarf stature and high salicylic acid of ceh1 and identified the mutation in a putative plastidial metalloprotease (VIR3). Biochemical analyses showed increased VIR3 levels in ceh1, accompanied by reduced abundance of VIR3-target enzymes, ascorbate peroxidase, and glyceraldehyde 3-phophate dehydrogenase B. These proteomic shifts elicited increased H2O2, salicylic acid, and MEcPP levels, as well as stromule formation. High light recapitulated VIR3-associated reconfiguration of plastidial metabolic and structural states. These results establish a link between a plastidial stress-inducible retrograde signaling metabolite and a putative metalloprotease and reveal how the reciprocity between the two components modulates plastidial metabolic and structural states, shaping adaptive responses.

Reassessing the evolution of the 1-deoxy-D-xylulose 5-phosphate synthase family suggests a possible novel function for the DXS class 3 proteins

The methylerythritol 4-phosphate (MEP) pathway is of paramount importance for generating plastidial isoprenoids. The first enzyme of the MEP pathway, 1-deoxy-D-xylulose-5-phosphate synthase (DXS), catalyzes a flux-controlling step. In plants the DXS gene family is composed of three distinct classes with non-redundant functions. Although the DXS1 and DXS2 subfamilies have been well characterized, the DXS3 subfamily has been considerably understudied. Here, we carried out in silico and functional analyses to better understand the DXS3 class. Our phylogenetic analysis showed high variation in copy number among the different DXS classes, with the apparent absence of DXS1 class in some species. We found that DXS3 subfamily emerged later than DXS1 and DXS2 and it is under less intense purifying selection. Furthermore, in the DXS3 subfamily critical amino acids positions in the thiamine pyrophosphate binding pocket are not conserved. We demonstrated that the DXS3 proteins from Arabidopsis, Maize, and Rice lack functional DXS activity. Moreover, the Arabidopsis DXS3 protein displayed distinctive sub-organellar chloroplast localization not observed in any DXS1 or DXS2 proteins. Co-expression analysis of the DXS3 from Arabidopsis showed that, unlike DXS1 and DXS2 proteins, it co-expresses with genes related to post-embryonic development and reproduction and not with primary metabolism and isoprenoid synthesis.

Channeling of Carbon Flux Towards Carotenogenesis in Botryococcus braunii: A Media Engineering Perspective

Microalgae, due to their unique properties, gained attention for producing promising feedstocks having high contents of proteins, antioxidants, carotenoids, and terpenoids for applications in nutraceutical and pharmaceutical industries. Optimizing production of the high-value renewables (HVRs) in microalgae requires an in-depth understanding of their functional relationship of the genes involved in these metabolic pathways. In the present study, bioinformatic tools were employed for characterization of the protein-encoding genes of methyl erythritol phosphate (MEP) pathway involved in carotenoid and squalene biosynthesis based upon their conserved motif/domain organization. Our analysis demonstrates nearly 200 putative genes showing a conservation pattern within divergent microalgal lineages. Furthermore, phylogenomic studies confirm the close evolutionary proximity among these microalgal strains in the carotenoid and squalene biosynthetic pathways. Further analysis employing STRING predicts interactions among two rate-limiting genes, i.e., phytoene synthase (PSY) and farnesyl diphosphate farnesyl synthase (FPPS), which are specifically involved in the synthesis of carotenoids and squalene. Experimentally, to understand the carbon flux of these rate-limiting genes involved in carotenogenesis, an industrial potential strain, namely, Botryococcus braunii, was selected in this study for improved biomass productivity (i.e., 100 mg L^-1 D^-1) along with enhanced carotenoid content [0.18% dry cell weight (DCW)] when subjected to carbon supplementation. In conclusion, our approach of media engineering demonstrates that the channeling of carbon flux favors carotenogenesis rather than squalene synthesis. Henceforth, employing omics perspectives will further provide us with new insights for engineering regulatory networks for enhanced production of high-value carbon biorenewables without compromising growth.