AabHLH112, a bHLH transcription factor, positively regulates sesquiterpenes biosynthesis in Artemisia annua

Comparative transcriptome analysis reveals abscisic acid-induced bHLH transcription factors involved in saikosaponin biosynthesis in Bupleurum chinense DC

Bupleurum chinense DC. a medicinal plant valued for saikosaponins (SSs) with antipyretic and hepatoprotective properties, faces constrained SS biosynthesis mediated by abscisic acid (ABA) during growth. Basic helix-loop-helix (bHLH) transcription factors (TFs) are hypothesized to participate in ABA signaling cascades, but their mechanistic role in SS regulation remains undefined. In this study, 20 differentially expressed BcbHLH genes were identified by transcriptomic profiling of ABA-induced hairy roots, with four MYC-family candidates (BcbHLH1-BcbHLH4) demonstrating ABA-responsive regulatory potential. ABA exposure (100 or 200 μmol/L, 24-72 h) induced dose-dependent SS reduction, while correlation analyses revealed coordinated expression between BcbHLH1-BcHMGR (r = 0.62) and BcbHLH4-BcBAS (r = 0.78), pinpointing these TFs as critical nodes in SS pathway modulation. Tissue-specific profiling showed predominant BcbHLH expression in stems and young leaves, with nuclear localization confirming their transcriptional regulatory organelles. BcbHLH3/4 exhibited transcriptional activation activity in the MYC_N domain, while molecular docking predicted 11th Arginine in the HLH domain as essential for G-box DNA binding. Collectively, our findings suggest that BcbHLH1-BcbHLH4 may serve as potential switches for fine-tuning ABA responsiveness in SS biosynthesis. Strategic manipulation of BcbHLH activity through genetic engineering approaches such as CRISPR-based editing or overexpression could alleviate ABA-mediated biosynthetic repression. Furthermore, precision engineering of the critical functional domain in BcbHLH could enhance promoter-binding activity to target genes and improve SS biosynthesis efficiency. These findings provide a reference framework for harnessing transcriptional regulators to optimize SS production in Bupleurum chinense DC.

Engineering scutellarin biosynthesis in Artemisia annua

KEY MESSAGE

Heterologous synthesis of scutellarin was successfully achieved in Artemisia annua by supplementing missing enzymes and optimizing flavone 6 hydroxylase in the biosynthetic pathway after identifying two crucial precursors in wild type plants. Artemisia annua, a plant renowned for its antimalarial properties, harbors a diverse array of terpenoids, phenols and other natural products along with their respective precursors. Engineering A. annua plants through synthetic biology holds significant promise to produce drugs in scarcity. Herein, we identified two essential precursors of scutellarin, an ingredient known for its remarkable therapeutic efficacy in treating cerebrovascular and cardiovascular diseases, within wild-type A. annua plants. To facilitate the heterologous synthesis of this bioactive compound in A. annua, we co-expressed three key genes derived from the original host, Erigeron breviscapus: the flavone synthase II gene (EbFSII), the flavonoid-7-O-glucuronosyltransferase gene (EbF7GAT), and the flavone-6-hydroxylase gene (EbF6H). These engineered plants successfully synthesized scutellarin at levels ranging from 0.18 to 0.24 mg/g DW. Furthermore, the introduction of the flavone-6-hydroxylase gene from Scutellaria baicalensis (SbF6H), which demonstrated superior catalytic activity, significantly increased scutellarin generation, achieving concentrations of up to 0.64 mg/g DW. Notably, the insertion of these exogenous genes did not negatively affect the synthesis of artemisinin and its derivatives in A. annua. These findings suggest that A. annua offers a formidable foundation for the biosynthesis of scutellarin. Additionally, the results imply that enhancing the activity of critical enzymes boosts the yield of the valuable terminal products.

AaMYB121, a Novel R2-MYB-like Transcription Factor, Regulates Artemisinin Biosynthesis in Artemisia annua

Artemisinin, a crucial antimalarial compound synthesized in Artemisia annua, is tightly controlled by various transcription factors. Despite significant progress in understanding this regulatory network, further exploration of additional factors is needed to improve artemisinin biosynthesis. Here, we identified a novel R2-MYB-like transcription factor, AaMYB121, which responds to methyl jasmonate (MeJA). Overexpression of AaMYB121 in transgenic A. annua plants resulted in dihydroartemisinic acid (DHAA) content being elevated 2~3 times compared to the control, while artemisinin levels increased to 1.4~2 times, significantly boosting artemisinin biosynthesis. Dual-Luciferase (Dual-LUC) assay and yeast one-hybrid (Y1H) analysis demonstrated that AaMYB121 directly binds to the promoter motifs of DBR2 (-1146~-1103) and ALDH1 (-1558~-1504), thereby triggering the transcriptional initiation of these genes. Notably, AaMYB121 features an elongated DNA-binding domain that specifically recognizes AT-rich cis-elements in the promoters of key artemisinin biosynthetic genes. These findings established AaMYB121 as a novel MYB-like transcription factor with strong potential to enhance the regulation of artemisinin production through targeted modulation, offering a valuable approach to improve artemisinin yields for therapeutic purposes.

Comprehensive characterization of the bHLH transcription factor family in Curcuma wenyujin and functional elucidation of CwbHLH27 in jasmonate-regulated sesquiterpenoid biosynthesis

Curcuma wenyujin is acknowledged as a crucial medicinal plant containing essential oils, primarily composed of sesquiterpenoids. While numerous sesquiterpenoids exhibit versatile physiological activities, their levels in C. wenyujin are generally low, particularly the pivotal anti-cancer component elemene. Our previous research demonstrated that basic helix-loop-helix (bHLH) is involved in modulating jasmonate-mediated sesquiterpenoid biosynthesis. In this study, a total of 106 CwbHLHs were identified and systematically analyzed. Under MeJA treatment, the expression levels of CwbHLH15, CwbHLH27, CwbHLH58, CwbHLH73, and CwbHLH89 were significantly upregulated, whereas CwbHLH81 was downregulated. Subsequently, CwbHLH27 was selected for further functional characterization. CwbHLH27 overexpression resulted in increased levels of β-elemene, γ-elemene, β-caryophyllene, and curzerene in C. wenyujin leaves. The expression levels of CwHMGS, CwHMGR, CwDXS, CwDXR, CwFPPS, and CwHDR, key enzyme genes in sesquiterpenoid biosynthesis, were upregulated in transgenic lines. Conversely, CwbHLH27 silencing resulted in the opposite effects. Further analysis revealed that CwbHLH27 activated the transcription of CwHMGS, CwHMGR, and CwDXS by directly binding to the E-box cis-elements within their promoters. Moreover, CwbHLH27 interacts with CwJAZ1/17, thereby executing JA signal transduction and regulating sesquiterpenoid biosynthesis in C. wenyujin. Finally, we elucidated the molecular mechanism by which the CwJAZs-CwbHLH27 regulatory module regulates sesquiterpenoid biosynthesis in response to JA signaling. Our research provides a molecular foundation for biotechnological-assisted breeding of varieties with enhanced active ingredient content.

Genome-wide characterization and expression analysis of the bHLH gene family in response to abiotic stresses in Zingiber officinale Roscoe

BACKGROUND

The basic helix-loop-helix (bHLH) transcription factors play important physiological functions in the processes of plant growth, development, and response to abiotic stresses. However, a comprehensive genome-scale study of the ginger bHLH gene family has not been documented.

RESULTS

In this study, 142 ZobHLH genes were identified in the ginger genome. Using Arabidopsis bHLH proteins as a reference, ZobHLH genes were classified into 15 subfamilies and unevenly distributed on 11 chromosomes of ginger. Sequence characterization, multiple sequence alignment, phylogenetic analysis, conserved protein motifs and exon-intron distribution patterns were conducted to further analyze the evolutionary relationships among these ZobHLH proteins. The results of the duplicated event analysis demonstrated that the pivotal role of segment duplication in promoting the expansion of the ZobHLH gene family. Additionally, analysis of cis-regulatory elements as well as protein interaction networks indicated the potential involvement of ginger ZobHLH family proteins in plant growth and development, and response to adversity stress. RNA-seq and RT-qPCR results showed that ZobHLH083 and ZobHLH108 play key roles in response to salt stress and waterlogging stress, respectively.

CONCLUSION

In this study, we systematically analyzed the characteristics of ZobHLH proteins in ginger, discovering that these genes play critical roles in ginger rhizome expansion and response to salt and waterlogging stresses. The present study provides a theoretical foundation for the further research on ZobHLHs and will help to explore the functional properties of ZobHLH genes.

Genome-Wide Characterization and Analysis of the bHLH Gene Family in Perilla frutescens

Perilla frutescens (L.) Britt. is a traditional medicinal and culinary plant with a long history of cultivation and significant potential for broader utilization. The basic helix-loop-helix (bHLH) gene family is essential for regulating plant growth, development, stress responses, and secondary metabolism. However, the bHLH gene family in P. frutescens has not yet been characterized. In this study, a total of 205 bHLH genes were identified in P. frutescens through genome mining and analysis. Phylogenetic analysis classified these PfbHLH genes into 23 distinct subfamilies. Promoter analysis revealed an enrichment of cis-acting elements linked to plant hormone signaling and stress responses, suggesting their potential regulatory roles in development, growth, and stress adaptation. Expression profiling based on publicly available RNA-seq data demonstrated tissue-specific expression patterns of PfbHLH genes in roots, stems, and leaves. Four PfbHLH genes (PfbHLH66, PfbHLH45, PfbHLH13, and PfbHLH5) showed significant responses to methyl jasmonate (MeJA) induction. Yeast one-hybrid assays confirmed that these PfbHLH proteins could bind to the cis-acting G-box (CACGTG) element. This study offers new perspectives on the evolution, regulatory mechanisms, and functional roles of the bHLH gene family in P. frutescens. The findings deepen our understanding of the functional diversity within this gene family and establish a foundation for genetic enhancement and the biosynthesis of medicinal compounds in the species.

Chromosome-scale genome assembly of Docynia delavayi provides new insights into the α-farnesene biosynthesis

Docynia delavayi is an economically significant fruit species with a high market potential due to the special aroma of its fruit. Here, a 653.34 Mb high-quality genome of D. delavayi was first reported, of which 93.8 % of the sequences (612.98 Mb) could be anchored to 17 chromosomes, containing 48,325 protein-coding genes. Ks analysis proved that two whole genome duplication (WGD) events occurred in D. delavayi, resulting in the expansion of genes associated with terpene biosynthesis, which promoted its fruit-specific aroma production. Combined multi-omics analysis, α-farnesene was detected as the most abundant aroma substance emitted by D. delavayi fruit during storage, meanwhile one α-farnesene synthase gene (AFS) and 15 transcription factors (TFs) were identified as the candidate genes potentially involved in α-farnesene biosynthesis. Further studies for the regulation network of α-farnesene biosynthesis revealed that DdebHLH, DdeERF1 and DdeMYB could activate the transcription of DdeAFS. To our knowledge, it is the first report that MYB TF plays a regulatory role in α-farnesene biosynthesis, which will greatly facilitate future breeding programs for D. delavayi.

Advanced metabolic engineering strategies for increasing artemisinin yield in Artemisia annua L

Artemisinin, also known as 'Qinghaosu', is a chemically sesquiterpene lactone containing an endoperoxide bridge. Due to the high activity to kill Plasmodium parasites, artemisinin and its derivatives have continuously served as the foundation for antimalarial therapies. Natural artemisinin is unique to the traditional Chinese medicinal plant Artemisia annua L., and its content in this plant is low. This has motivated the synthesis of this bioactive compound using yeast, tobacco, and Physcomitrium patens systems. However, the artemisinin production in these heterologous hosts is low and cannot fulfil its increasing clinical demand. Therefore, A. annua plants remain the major source of this bioactive component. Recently, the transcriptional regulatory networks related to artemisinin biosynthesis and glandular trichome formation have been extensively studied in A. annua. Various strategies including (i) enhancing the metabolic flux in artemisinin biosynthetic pathway; (ii) blocking competition branch pathways; (iii) using transcription factors (TFs); (iv) increasing peltate glandular secretory trichome (GST) density; (v) applying exogenous factors; and (vi) phytohormones have been used to improve artemisinin yields. Here we summarize recent scientific advances and achievements in artemisinin metabolic engineering, and discuss prospects in the development of high-artemisinin yielding A. annua varieties. This review provides new insights into revealing the transcriptional regulatory networks of other high-value plant-derived natural compounds (e.g., taxol, vinblastine, and camptothecin), as well as glandular trichome formation. It is also helpful for the researchers who intend to promote natural compounds production in other plants species.

Genome-Wide Identification and Expression Analysis of the bHLH Transcription Factor Family in Wintersweet (Chimonanthus praecox)

Wintersweet (Chimonanthus praecox (L.) Link, Calycanthaceae) is an esteemed ornamental flowering shrub known for its distinct blooming period in winter, vibrant color petals, and captivating floral fragrance. Basic helix-loop-helix (bHLH) transcription factors (TFs) play pivotal roles as key regulators in secondary metabolites biosynthesis, growth, and development in plants. However, the systematic analysis of the bHLH family members and their role in the regulation of floral traits in Wintersweet remains insufficiently understood. To bridge this knowledge gap, we conducted a comprehensive genome-wide analysis of the C. praecox bHLH (CpbHLH) gene family, identifying a total of 131 CpbHLH genes across 11 chromosomes. Phylogenetic analysis classified these CpbHLH genes into 23 subfamilies, wherein most members within the same subfamily exhibited analogous intron/exon patterns and motif composition. Moreover, the expansion of the CpbHLH gene family was primarily driven by segmental duplication, with duplicated gene pairs experiencing purifying selection during evolution. Transcriptomic analysis revealed diverse expression patterns of CpbHLH genes in various tissues and distinct stages of Wintersweet flower development, thereby suggesting their involvement in a diverse array of physiological processes. Furthermore, yeast 2-hybrid assay demonstrated interaction between CpbHLH25 and CpbHLH59 (regulators of floral scent and color) as well as with CpbHLH112 and CpMYB2, suggesting potential coordinately regulation of secondary metabolites biosynthesis in Wintersweet flowers. Collectively, our comprehensive analysis provides valuable insights into the structural attributes, evolutionary dynamics, and expression profiles of the CpbHLH gene family, laying a solid foundation for further explorations of the multifaceted physiological and molecular roles of bHLH TFs in Wintersweet.