The 2-oxoglutarate-dependent dioxygenase superfamily participates in tanshinone production in Salvia miltiorrhiza

Phenanthrene metabolism in Panicum miliaceum: anatomical adaptations, degradation pathway, and computational analysis of a dioxygenase enzyme

Polycyclic aromatic compounds (PAHs) are persistent organic pollutants of environmental concern due to their potential impacts on food chain, with plants being particularly vulnerable. While plants can uptake, transport, and transform PAHs, the precise mechanisms underlying their localization and degradation are not fully understood. Here, a cultivation experiment conducted with Panicum miliaceum exposed different concentrations of phenanthrene (PHE). Intermediate PHE degradation compounds were identified via GC-MS analysis, leading to the proposal of a phytodegradation pathway featuring three significant benzene ring cleavage steps. Our results showed that P. miliaceum exhibited the ability to effectively degrade high levels of PHE, resulting in the production of various intermediate products through several chemical changes. Examination of the localization and anatomical characteristics revealed structural alterations linked to PHE stress, with an observed enhancement in PHE accumulation density in both roots and shoots as treatment levels increased. Following a 2-week aging period, a decrease in the amount of PHE accumulation was observed, along with a change in its localization. Bioinformatics analysis of the P. miliaceum 2-oxoglutarate-dependent dioxygenase (2-ODD) DAO-like protein revealed a 299 amino acid structure with two highly conserved domains, namely 2OG-FeII_Oxy and DIOX_N. Molecular docking analysis aligned with experimental results, strongly affirming the potential link and direct action of 2-ODD DAO-like protein with PHE. Our study highlights P. miliaceum capacity for PAHs degradation and elucidates the mechanisms behind enhanced degradation efficiency. By integrating experimental evidence with bioinformatics analysis, we offer valuable insights into the potential applications of plant-based remediation strategies for PAHs-contaminated environments.

Genome-wide characterization of 2OGD superfamily for mining of susceptibility factors responding to various biotic stresses in Musa spp

Bananas are an important staple food and cash crop, but they are vulnerable to a variety of pests and diseases that substantially reduce yield and quality. Banana diseases are challenging to control and necessitate an integrated strategy, and development of resistant cultivars is one of the effective ways of managing diseases. Lasting disease resistance is the main goal in crop improvement and resistance mediated by a single resistant (R) gene mostly lack durability. However, long-term resistance can be obtained by inactivating susceptibility factors (S), which facilitate pathogen infection and proliferation. Identification and inactivation of susceptibility factors against the major pathogens like Fusarium oxysporum f. sp. cubense (Foc), Pseudocercospora eumusae and Pratylenchus coffeae in banana will be an effective way in developing banana varieties with more durable resistance. Downy mildew resistance 6 (DMR6) and DMR-like oxygenases (DLO1) are one such susceptibility factors and they belong to 2-oxoglutarate Fe(II) dependent oxygenases (2OGD) superfamily. 2OGDs are known to catalyze a plethora of reactions and also confer resistance to different pathogens in various crops, but not much is known about the 2OGD in Musa species. Through a comprehensive genome-wide analysis, 133 and 122 potential 2OGDs were systematically identified and categorized from the A and B genomes of banana, respectively. Real time expression of dmr6 and dlo1 genes showed positive correlation with transcriptome data upon Foc race1 and TR4 infection and examination of expression pattern of Macma4_04_g22670 (Ma04_g20880) and Macma4_02_g13590 (Ma02_g12040) genes revealed their involvement in Foc race1 and TR4 infections, respectively. Further the expression profile of 2OGDs, specifically Macma4_04_g25310 (Ma04_g23390), Macma4_08_g11980 (Ma08_g12090) and Macma4_04_g38910 (Ma04_g36640) shows that they may play a significant role as a susceptibility factor, particularly against P. eumusae and P. coffeae, implying that they can be exploited as a candidate gene for editing in developing resistant cultivars against these diseases. In summary, our findings contribute to a deeper comprehension of the evolutionary and functional aspects of 2OGDs in Musa spp. Furthermore, they highlight the substantial functions of these family constituents in the progression of diseases. These insights hold significance in the context of enhancing the genetic makeup of bananas to attain extended and more durable resistance against pathogens.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01380-y.

Chromosome-level genome assembly of Salvia miltiorrhiza with orange roots uncovers the role of Sm2OGD3 in catalyzing 15,16-dehydrogenation of tanshinones

Salvia miltiorrhiza is well known for its clinical practice in treating heart and cardiovascular diseases. Its roots, used for traditional Chinese medicine materials, are usually brick-red due to accumulation of red pigments, such as tanshinone IIA and tanshinone I. Here we report a S. miltiorrhiza line (shh) with orange roots. Compared with the red roots of normal S. miltiorrhiza plants, the contents of tanshinones with a single bond at C-15,16 were increased, whereas those with a double bond at C-15,16 were significantly decreased in shh. We assembled a high-quality chromosome-level genome of shh. Phylogenomic analysis showed that the relationship between two S. miltiorrhiza lines with red roots was closer than the relationship with shh. It indicates that shh could not be the mutant of an extant S. miltiorrhiza line with red roots. Comparative genomic and transcriptomic analyses showed that a 1.0 kb DNA fragment was deleted in shh Sm2OGD3m. Complementation assay showed that overexpression of intact Sm2OGD3 in shh hairy roots recovered furan D-ring tanshinone accumulation. Consistently, in vitro protein assay showed that Sm2OGD3 catalyzed the conversion of cyptotanshinone, 15,16-dihydrotanshinone I and 1,2,15,16-tetrahydrotanshinone I into tanshinone IIA, tanshinone I and 1,2-dihydrotanshinone I, respectively. Thus, Sm2OGD3 functions as tanshinone 15,16-dehydrogenase and is a key enzyme in tanshinone biosynthesis. The results provide novel insights into the metabolic network of medicinally important tanshinone compounds.

Plant (di)terpenoid evolution: from pigments to hormones and beyond

Covering: up to 2014-2022.Diterpenoid biosynthesis in plants builds on the necessary production of (E,E,E)-geranylgeranyl diphosphate (GGPP) for photosynthetic pigment production, with diterpenoid biosynthesis arising very early in land plant evolution, enabling stockpiling of the extensive arsenal of (di)terpenoid natural products currently observed in this kingdom. This review will build upon that previously published in the Annual Review of Plant Biology, with a stronger focus on enzyme structure-function relationships, as well as additional insights into the evolution of (di)terpenoid metabolism since generated.

Hormone biosynthesis and metabolism members of 2OGD superfamily are involved in berry development and respond to MeJA and ABA treatment of Vitis vinifera L

BACKGROUND

Hormones play an indispensable role during fruit ripening, nine clades in 2-oxoglutarate-dependent dioxygenase (2OGD) superfamily are responsible for the hormone biosynthesis and metabolism, but less information is known about them.

RESULTS

A total of 163 Vv2OGD superfamily members were identified from grape genome, which were mainly expanded by local (tandem and proximal) duplication. Phylogenetic analysis of 2OGD members in grape and Arabidopsis indicates 37 members in Vv2OGD superfamily are related to hormone biosynthesis and metabolism process (Vv2OGD-H), which could be divided into 9 clades, gibberellin (GA) 3-oxidase (GA3ox), GA 20-oxidase (GA20ox), carbon-19 GA 2-oxidase (C₁₉-GA2ox), carbon-20 GA 2-oxidase (C₂₀-GA2ox), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), dioxygenase for auxin oxidation (DAO), lateral branching oxidoreductas (LBO), downy mildew resistant 6 and DMR6-like oxygenase (DMR6/DLO) and jasmonate-induced oxygenase (JOX). Sixteen of these 37 Vv2OGD-Hs are expressed in grape berry, in which the expression patterns of VvGA2oxs, VvDAOs and VvJOXs shows a correlation with the change patterns of GAs, indole-3-acetic acid (IAA) and jasmonates (JAs), indicating the involvement of these genes in grape berry development by regulating corresponding hormones. Twelve Vv2OGD-Hs respond to methyl JA (MeJA) treatment, of which eight may lead to the inhibition of the ripening process by the crosstalk of JAs-salicylic acids (SAs), JAs-GAs and JAs-JAs, while seven Vv2OGD-Hs respond to ABA treatment may be responsible for the promotion of ripening process by the interplay of abscisic acid (ABA)-strigolactones (SLs), ABA-SAs, ABA-GAs, ABA-JAs. Especially, VvLBO1 reach an expression peak near véraison and up-regulate about four times after ABA treatment, which implies SLs and ABA-SLs crosstalk may be related to the onset of berry ripening in grape.

CONCLUSIONS

This study provides valuable clues and new insights for the mechanism research of Vv2OGD-Hs in hormones regulation during the grape berry development.

Functional Characterization of a 2OGD Involved in Abietane-Type Diterpenoids Biosynthetic Pathway in Salvia miltiorrhiza

Salvia miltiorrhiza is one of the most commonly used Chinese medicinal herbs. Tanshinones, the most abundant lipid-soluble bioactive constituents of S. miltiorrhiza, are a class of structural highly oxidized abietane-type diterpenoids with multiple pharmacological activities. Although several enzymes, including diterpene synthase, cytochrome P450, and Fe(II)/2-oxoglutarate-dependent dioxygenase (2OGD), have been functionally characterized in biosynthesis of abietane-type diterpenoids, the highly oxidized structure and complex secondary metabolic network of tanshinones imply that more oxidases should be characterized. Here, we identified a new 2OGD (Sm2OGD25) from S. miltiorrhiza. Molecular cloning and functional studies in vitro showed that Sm2OGD25 could catalyze the hydroxylation of sugiol at C-15 and C-16 positions to produce hypargenin B and crossogumerin C, respectively. The phylogenetic analysis of the DOXC family demonstrated that Sm2OGD25 belongs to the DOXC54 clade. Furthermore, structural modeling and site-directed mutagenesis characterization revealed the importance of the hydrogen-bonding residue Y339 and the hydrophobic residues (V122, F129, A144, A208, F303, and L344) in substrate binding and enzyme activity. This study will promote further studies on the catalytic characterization of plant 2OGDs and the secondary metabolic biosynthesis network of diterpenoids.

One-Step Regeneration of Hairy Roots to Induce High Tanshinone Plants in Salvia miltiorrhiza

Salvia miltiorrhiza is a traditional Chinese medicinal plant of Labiatae, which has been widely utilized to treat a variety of cardiovascular and cerebrovascular diseases. However, due to the long growth cycle, low content of active ingredients, and serious quality deterioration of S. miltiorrhiza, the use of biotechnology to improve S. miltiorrhiza to meet the growing demand for clinical applications has become a research hotspot. In this study, a novel one-step hairy root regeneration method was developed, which could rapidly obtain hairy roots and regenerated plants with high tanshinone content. By optimizing the parameters of Agrobacterium rhizogenes transformation in S. miltiorrhiza, it was finally established that the explants were infected in Ar.qual (OD₆₀₀ = 0.6) for 10 min, co-cultured for 3 days, and then screened on the screening medium containing 7.5 mg/l hygromycin, the maximum transformation frequency can reach 73.85%. GFP and PCR detection yielded a total of 9 positive transgenic hairy root lines and 11 positive transgenic regenerated plants. SmGGPPS1 was successfully overexpressed in positive transgenic regenerated plants, according to the results of qRT-PCR. The content of tanshinone IIA and cryptotanshinone were dramatically enhanced in transgenic regenerated plants and hairy roots by Ultra Performance Liquid Chromatography analysis. Based on the Agrobacterium-mediated transformation of S. miltiorrhiza, this study developed a new method for regenerating plants with transgenic hairy roots. This method provides a foundation for the breeding of S. miltiorrhiza and the sustainable development of medicinal plant resources, as well as provides a useful reference for the application of other species.

AetSRG1 contributes to the inhibition of wheat Cd accumulation by stabilizing phenylalanine ammonia lyase

Cadmium (Cd) is a toxic heavy metal that poses a serious threat to crop safety, productivity, and human health. Aegilops tauschii is the D genome donor of common wheat and shows abundant genetic variation. However, the tolerance of Ae. tauschii toward Cd at the molecular level is poorly understood. In this study, key factors involved in the Cd stress response of Ae. tauschii were investigated by RNA sequencing. Differentially expressed genes (DEGs) under Cd stress were identified in Ae. tauschii roots and shoots. A Fe(II)/2-oxoglutarate dependent dioxygenase (designated as AetSRG1), with an unknown function in Cd stress, was of particular interest. The open reading frame of AetSRG1 was cloned and overexpressed in wheat, which resulted in reduced Cd accumulation along with a lower Cd²⁺ flux, decreased electrolyte leakage, and higher reactive oxygen species production. The protein of AetSRG1 interacted with phenylalanine ammonia lyase (PAL). Finally, we found that AetSRG1 stabilizes PAL and promotes the synthesis of endogenous salicylic acid. This study provides novel insights into the molecular mechanisms underlying the response of Ae. tauschii toward Cd stress. The key genes identified in this work serve as potential targets for developing low cadmium wheat.

Tanshinones: Leading the way into Lamiaceae labdane-related diterpenoid biosynthesis

Tanshinones are the bioactive diterpenoid constituents of the traditional Chinese medicinal herb Danshen (Salvia miltiorrhiza), and are examples of the phenolic abietanes widely found within the Lamiaceae plant family. Due to the significant interest in these labdane-related diterpenoid natural products, their biosynthesis has been intensively investigated. In addition to providing the basis for metabolic engineering efforts, this work further yielded pioneering insights into labdane-related diterpenoid biosynthesis in the Lamiaceae more broadly. This includes stereochemical foreshadowing of aromatization, with novel protein domain loss in the relevant diterpene synthase, as well as broader phylogenetic conservation of the relevant enzymes. Beyond such summary of more widespread metabolism, formation of the furan ring that characterizes the tanshinones also has been recently elucidated. Nevertheless, the biocatalysts for the pair of demethylations remain unknown, and the intriguing potential connection of these reactions to the further aromatization observed in the tanshinones are speculated upon here.

A 2-oxoglutarate-dependent dioxygenase converts dihydrofuran to furan in Salvia diterpenoids

Tanshinone ⅡA (TⅡA), a diterpene quinone with a furan ring, is a bioactive compound found in the medicinal herb redroot sage (Salvia miltiorrhiza Bunge), in which both furan and dihydrofuran analogs are present in abundance. Progress has been made recently in elucidating the tanshinone biosynthetic pathway, including heterocyclization of the dihydrofuran D-ring by cytochrome P450s; however, dehydrogenation of dihydrofuran to furan, a key step of furan ring formation, remains uncharacterized. Here, by differential transcriptome mining, we identified six 2-oxoglutarate-dependent dioxygenase (2-ODD) genes whose expressions corresponded to tanshinone biosynthesis. We showed that Sm2-ODD14 acts as a dehydrogenase catalyzing the furan ring aromatization. In vitro Sm2-ODD14 converted cryptotanshinone to TⅡA and thus was designated TⅡA synthase (SmTⅡAS). Furthermore, SmTⅡAS showed a strict substrate specificity, and repression of SmTⅡAS expression in hairy root by RNAi led to increased accumulation of total dihydrofuran-tanshinones and decreased production of furan-tanshinones. We conclude that SmTⅡAS controls the metabolite flux from dihydrofuran- to furan-tanshinones, which influences medicinal properties of S. miltiorrhiza.

Integrated Transcriptomics and Proteomics to Reveal Regulation Mechanism and Evolution of SmWRKY61 on Tanshinone Biosynthesis in Salvia miltiorrhiza and Salvia castanea

Tanshinones found in Salvia species are the main active compounds for the treatment of cardiovascular and cerebrovascular diseases, but their contents are hugely different in different species. For example, tanshinone IIA content in Salvia castanea Diels f. tomentosa Stib. is about 49 times higher than that in Salvia miltiorrhiza Bunge. The molecular mechanism responsible for this phenomenon remains largely unknown. To address this, we performed comparative transcriptomic and proteomic analyses of S. miltiorrhiza and S. castanea. A total of 296 genes in S. castanea and 125 genes in S. miltiorrhiza were highly expressed at both the transcriptional and proteome levels, including hormone signal regulation, fungus response genes, transcription factors, and CYP450. Among these differentially expressed genes, the expression of SmWRKY61 was particularly high in S. castanea. Overexpression of SmWRKY61 in S. miltiorrhiza could significantly increase the content of tanshinone I and tanshinone IIA, which were 11.09 and 33.37 times of the control, respectively. Moreover, SmWRKY61 had a strong regulatory effect, elevating the expression levels of tanshinone pathway genes such as DXS2, CMK, HMGS2, 1, KSL1, KSL2, CYP76AH1, and CYP76AK3. For the WRKY family, 79 SmWRKYs were originally obtained and classified into three main groups. Collinearity analysis indicated a more specific extension of WRKY gene family in Salvia genus. In 55 Salvia species, only 37 species contained the WRKY61 sequence, and high SmWRKY61 expression in some Salvia L. species was often accompanied by high tanshinone accumulation. The above results suggest that SmWRKY61 is a highly effective regulator of tanshinone accumulation and may be a key factor resulting in high tanshinone accumulation in S. castanea.

Genome-Wide Identification of Circular RNAs Potentially Involved in the Biosynthesis of Secondary Metabolites in Salvia miltiorrhiza

Circular RNAs (circRNAs) play various roles in cellular functions. However, no studies have been reported on the potential involvement of circRNAs in the biosynthesis of secondary metabolites in plants. Here, we performed a genome-wide discovery of circRNAs from root, stem and leaf samples of Salvia miltiorrhiza using RNA-Seq. We predicted a total of 2,476 circRNAs with at least two junction reads using circRNA_finder and CIRI, of which 2,096, 151 and 229 were exonic, intronic and intergenic circRNAs, respectively. Sequence similarity analysis showed that 294 out of 2,476 circRNAs were conserved amongst multiple plants. Of the 55 predicted circRNAs, 31 (56%) were validated successfully by PCR and Sanger sequencing using convergent and divergent primer pairs. Alternative circularisation analysis showed that most parental genes produced two circRNAs. Functional enrichment analyses of the parental genes showed that the primary metabolism pathways were significantly enriched, particularly the carbon metabolism. Differential expression analysis showed that the expression profiles of circRNAs were tissue-specific. Co-expression analysis showed 275 circRNAs, and their parental genes had significantly positive correlations. However, 14 had significantly negative correlations. Weighted gene co-expression network analysis showed that nine circRNAs were co-expressed with four modules of protein-coding genes. Next, we found 416 exonic circRNAs with miRNA-binding sites, suggesting possible interactions between circRNAs and miRNAs. Lastly, we found six validated circRNAs, namely, SMscf2473-46693-46978, SMscf3091-29256-29724, SMscf16-111773-112193, SMscf432-13232-13866, SMscf7007-10563-10888 and SMscf1730-1749-2013, which were originated from the genes involved in the biosynthesis of secondary metabolites. Their parental genes were acetyl-CoA C-acetyltransferase 1 (SmAACT1), 1-deoxy-d-xylulose-5-phosphate synthase 2 (SmDXS2), 4-hydroxy-3-methylbut-2-enyl diphosphate reductase 1 (SmHDR1), kaurene synthase-like 2 (SmKSL2), DWF4 and CYP88A3, respectively. In particular, the correlation coefficient of SMscf2473-46693-46978 and SmDXS2 gene was 0.86 (p = 0.003), indicating a potential interaction between this pair of circRNA and its parent gene. Our results provided the first comprehensive catalogue of circRNAs in S. miltiorrhiza and identified one circRNA that might play important roles in the biosynthesis of secondary metabolites.

Genome-Wide Identification and Expression Profiling of 2OGD Superfamily Genes from Three Brassica Plants

The 2-oxoglutarate and Fe(II)-dependent dioxygenase (2OGD) superfamily is the second largest enzyme family in the plant genome, and its members are involved in various oxygenation and hydroxylation reactions. Due to their important biochemical significance in metabolism, a systematic analysis of the plant 2OGD genes family is necessary. Here, we identified 160, 179, and 337 putative 2OGDs from Brassica rapa, Brassica oleracea, and Brassica napus. According to their gene structure, domain, phylogenetic features, function, and previous studies, we also divided 676 2OGDs into three subfamilies: DOXA, DOXB, and DOXC. Additionally, homologous and phylogenetic comparisons of three subfamily genes provided valuable insight into the evolutionary characteristics of the 2OGD genes from Brassica plants. Expression profiles derived from the transcriptome and Genevestigator database exhibited distinct expression patterns of the At2OGD, Br2OGD, and Bo2OGD genes in different developmental stages, tissues, or anatomical parts. Some 2OGD genes showed high expression levels in various tissues, such as callus, seed, silique, and root tissues, while other 2OGD genes were expressed at very low levels in other tissues. Analysis of six Bo2OGD genes in different tissues by qRT-PCR indicated that these genes are involved in the metabolism of gibberellin, which in turn regulates plant growth and development. Our working system analysed 2OGD gene families of three Brassica plants and laid the foundation for further study of their functional characterization.

Recent progress and new perspectives for diterpenoid biosynthesis in medicinal plants

Diterpenoids, including more than 18,000 compounds, represent an important class of metabolites that encompass both phytohormones and some industrially relevant compounds. These molecules with complex, diverse structures and physiological activities, have high value in the pharmaceutical industry. Most medicinal diterpenoids are extracted from plants. Major advances in understanding the biosynthetic pathways of these active compounds are providing unprecedented opportunities for the industrial production of diterpenoids by metabolic engineering and synthetic biology. Here, we summarize recent developments in the field of diterpenoid biosynthesis from medicinal herbs. An overview of the pathways and known biosynthetic enzymes is presented. In particular, we look at the main findings from the past decade and review recent progress in the biosynthesis of different groups of ringed compounds. We also discuss diterpenoid production using synthetic biology and metabolic engineering strategies, and draw on new technologies and discoveries to bring together many components into a useful framework for diterpenoid production.

Genome-wide characterization of 2-oxoglutarate and Fe(II)-dependent dioxygenase family genes in tomato during growth cycle and their roles in metabolism

BACKGROUND

2-Oxoglutarate and Fe(II)-dependent dioxygenases (2ODDs) belong to the 2-oxoglutarate-dependent dioxygenase (2OGD) superfamily and are involved in various vital metabolic pathways of plants at different developmental stages. These proteins have been extensively investigated in multiple model organisms. However, these enzymes have not been systematically analyzed in tomato. In addition, type I flavone synthase (FNSI) belongs to the 2ODD family and contributes to the biosynthesis of flavones, but this protein has not been characterized in tomato.

RESULTS

A total of 131 2ODDs from tomato were identified and divided into seven clades by phylogenetic classification. The Sl2ODDs in the same clade showed similar intron/exon distributions and conserved motifs. The Sl2ODDs were unevenly distributed across the 12 chromosomes, with different expression patterns among major tissues and at different developmental stages of the tomato growth cycle. We characterized several Sl2ODDs and their expression patterns involved in various metabolic pathways, such as gibberellin biosynthesis and catabolism, ethylene biosynthesis, steroidal glycoalkaloid biosynthesis, and flavonoid metabolism. We found that the Sl2ODD expression patterns were consistent with their functions during the tomato growth cycle. These results indicated the significance of Sl2ODDs in tomato growth and metabolism. Based on this genome-wide analysis of Sl2ODDs, we screened six potential FNSI genes using a phylogenetic tree and coexpression analysis. However, none of them exhibited FNSI activity.

CONCLUSIONS

Our study provided a comprehensive understanding of the tomato 2ODD family and demonstrated the significant roles of these family members in plant metabolism. We also suggest that no FNSI genes in tomato contribute to the biosynthesis of flavones.

Metabolomics reveals the influences of smoke-water and karrikinolide on the biosynthesis of flavonoids and terpenoids in Salvia miltiorrhiza

Metabolomics was used to study the influences of smoke-water (SW) and karrikinolide (KAR1) on the biosynthesis of flavonoids and terpenoids in Salvia miltiorrhiza Bunge. The results showed that a total of 178 and 199 differential metabolites were obtained in SW and KAR1, respectively, compared to the control. The differential metabolites were assigned to the corresponding metabolic pathways. The results indicated that some metabolic pathways in treatments of SW and KAR1 overlapped, suggesting that treatments of SW and KAR1 showed similar effects on the metabolic mechanism of S. miltiorrhiza. To obtain a clear overview of changes in metabolic regulation, TCA cycle, glycolytic pathway, biosynthesis of flavonoids and terpenoids and amino acids metabolism pathway were mapped into a network. We found that treatments with SW and KAR1 could significantly promote the biosynthesis of flavonoids and terpenoids in S. miltiorrhiza. This study could help us better understand the influences of SW and KAR1 on secondary metabolites and their underlying mechanism.

Comparative Genome Analysis of Scutellaria baicalensis and Scutellaria barbata Reveals the Evolution of Active Flavonoid Biosynthesis

Scutellaria baicalensis (S. baicalensis) and Scutellaria barbata (S. barbata) are common medicinal plants of the Lamiaceae family. Both produce specific flavonoid compounds, including baicalein, scutellarein, norwogonin, and wogonin, as well as their glycosides, which exhibit antioxidant and antitumor activities. Here, we report chromosome-level genome assemblies of S. baicalensis and S. barbata with quantitative chromosomal variation (2n = 18 and 2n = 26, respectively). The divergence of S. baicalensis and S. barbata occurred far earlier than previously reported, and a whole-genome duplication (WGD) event was identified. The insertion of long terminal repeat elements after speciation might be responsible for the observed chromosomal expansion and rearrangement. Comparative genome analysis of the congeneric species revealed the species-specific evolution of chrysin and apigenin biosynthetic genes, such as the S. baicalensis-specific tandem duplication of genes encoding phenylalanine ammonia lyase and chalcone synthase, and the S. barbata-specific duplication of genes encoding 4-CoA ligase. In addition, the paralogous duplication, colinearity, and expression diversity of CYP82D subfamily members revealed the functional divergence of genes encoding flavone hydroxylase between S. baicalensis and S. barbata. Analyzing these Scutellaria genomes reveals the common and species-specific evolution of flavone biosynthetic genes. Thus, these findings would facilitate the development of molecular breeding and studies of biosynthesis and regulation of bioactive compounds.

Transcriptome profiling at osmotic and ionic phases of salt stress response in bread wheat uncovers trait-specific candidate genes

BACKGROUND

Bread wheat is one of the most important crops for the human diet, but the increasing soil salinization is causing yield reductions worldwide. Improving salt stress tolerance in wheat requires the elucidation of the mechanistic basis of plant response to this abiotic stress factor. Although several studies have been performed to analyze wheat adaptation to salt stress, there are still some gaps to fully understand the molecular mechanisms from initial signal perception to the onset of responsive tolerance pathways. The main objective of this study is to exploit the dynamic salt stress transcriptome in underlying QTL regions to uncover candidate genes controlling salt stress tolerance in bread wheat. The massive analysis of 3'-ends sequencing protocol was used to analyze leave samples at osmotic and ionic phases. Afterward, stress-responsive genes overlapping QTL for salt stress-related traits in two mapping populations were identified.

RESULTS

Among the over-represented salt-responsive gene categories, the early up-regulation of calcium-binding and cell wall synthesis genes found in the tolerant genotype are presumably strategies to cope with the salt-related osmotic stress. On the other hand, the down-regulation of photosynthesis-related and calcium-binding genes, and the increased oxidative stress response in the susceptible genotype are linked with the greater photosynthesis inhibition at the osmotic phase. The specific up-regulation of some ABC transporters and Na+/Ca2+ exchangers in the tolerant genotype at the ionic stage indicates their involvement in mechanisms of sodium exclusion and homeostasis. Moreover, genes related to protein synthesis and breakdown were identified at both stress phases. Based on the linkage disequilibrium blocks, salt-responsive genes within QTL intervals were identified as potential components operating in pathways leading to salt stress tolerance. Furthermore, this study conferred evidence of novel regions with transcription in bread wheat.

CONCLUSION

The dynamic transcriptome analysis allowed the comparison of osmotic and ionic phases of the salt stress response and gave insights into key molecular mechanisms involved in the salt stress adaptation of contrasting bread wheat genotypes. The leveraging of the highly contiguous chromosome-level reference genome sequence assembly facilitated the QTL dissection by targeting novel candidate genes for salt tolerance.

Genome-wide identification of the maize 2OGD superfamily genes and their response to Fusarium verticillioides and Fusarium graminearum

In maize, eat rot and stalk rot caused by Fusarium verticillioides and Fusarium graminearum lead to contamination of moldy grains to produce mycotoxins. Identification of resistance genes against these pathogens for maize breeding is an effective way for disease control. Several 2-oxoglutarate-dependent dioxygenase (2OGD) proteins have been found to confer resistance to different pathogens in diverse plant species. However, little is known about the 2OGD superfamily in maize. Here, we identified 103 putative 2OGD genes in maize from a genome-wide analysis, and divided them into three classes - DOXA, DOXB, and DOXC. We further comprehensively investigated their gene structure, chromosome distribution, phylogenetic tree, gene-function enrichment, and expression profiles among different tissues. The genes encoding three 2OGD proteins, ACO, F3H, and NCS involved in ethylene biosynthesis, flavonoids biosynthesis, and alkaloids biosynthesis pathways, respectively, were identified to be induced by F. verticillioides and F. graminearum. The promoters of the three genes contain the binding sites for the transcription factor ZmDOF and ZmHSF, which are also induced by the two pathogens. The results imply that the three 2OGDs and the two transcription factors might be involved in the resistance to the two pathogens. This study provided a comprehensive understanding of the 2OGD superfamily in maize and laid the foundation for the further functional analysis of their roles in maize resistance to eat rot and stalk rot.

Tanshinone and salvianolic acid biosynthesis are regulated by SmMYB98 in Salvia miltiorrhiza hairy roots

Salvia miltiorrhiza Bunge is an herb rich in bioactive tanshinone and salvianolic acid compounds. It is primarily used as an effective medicine for treating cardiovascular and cerebrovascular diseases. Liposoluble tanshinones and water-soluble phenolic acids are a series of terpenoids and phenolic compounds, respectively. However, the regulation mechanism for the simultaneous promotion of tanshinone and salvianolic acid biosynthesis remains unclear. This study identified a R2R3-MYB subgroup 20 transcription factor (TF), SmMYB98, which was predominantly expressed in S. miltiorrhiza lateral roots. The accumulation of major bioactive metabolites, tanshinones, and salvianolic acids, was improved in SmMYB98 overexpression (OE) hairy root lines, but reduced in SmMYB98 knockout (KO) lines. The qRT-PCR analysis revealed that the transcriptional expression levels of tanshinone and salvianolic acid biosynthesis genes were upregulated by SmMYB98-OE and downregulated by SmMYB98-KO. Dual-Luciferase (Dual-LUC) assays demonstrated that SmMYB98 significantly activated the transcription of SmGGPPS1, SmPAL1, and SmRAS1. These results suggest that SmMYB98-OE can promote tanshinone and salvianolic acid production. The present findings illustrate the exploitation of R2R3-MYB in terpenoid and phenolic biosynthesis, as well as provide a feasible strategy for improving tanshinone and salvianolic acid contents by MYB proteins in S. miltiorrhiza.

Genome-Wide Characterization and Analysis of bHLH Transcription Factors Related to Crocin Biosynthesis in Gardenia jasminoides Ellis (Rubiaceae)

Crocins, enriched in Gardenia jasminoides fruits, have a pharmacological activity against central nervous system diseases, cardiovascular diseases, and cancer cell growth. The biosynthesis of crocins has been widely explored, but its regulatory mechanism remains unknown. Here, the basic helix-loop-helix (bHLH) transcription factors related to crocin biosynthesis were systematically identified on the basis of the genome of G. jasminoides. A total of 95 GjbHLH transcription factor genes were identified, and their phylogenetic analysis indicated that they could be classified into 23 subfamilies. The combination of gene-specific bHLH expression patterns, the coexpression analysis of biosynthesis genes, and the analysis of promoter sequences in crocin biosynthesis pathways suggested that nine bHLHs in G. jasminoides might negatively regulate crocin biosynthesis. This study laid a foundation for understanding the regulatory mechanism of crocin biosynthesis and the improvement and breeding of G. jasminoides varieties.

Transcriptomic analysis reveals potential genes involved in tanshinone biosynthesis in Salvia miltiorrhiza

Tanshinones are important bioactive components in Salvia miltiorrhiza and mainly accumulate in the periderms of mature roots. Tanshinone biosynthesis is a complicated process, and little is known about the third stage of the pathway. To investigate potential genes that are responsible for tanshinone biosynthesis, we conducted transcriptome profiling analysis of two S. miltiorrhiza cultivars. Differential expression analysis provided 2,149 differentially expressed genes (DEGs) for further analysis. GO and KEGG analysis showed that the DEGs were mainly associated with the biosynthesis of secondary metabolites. Weighted gene coexpression network analysis (WGCNA) was further performed to identify a “cyan” module associated with tanshinone biosynthesis. In this module, 25 cytochromes P450 (CYPs), three 2-oxoglutarate-dependent dioxygenases (2OGDs), one short-chain alcohol dehydrogenases (SDRs) and eight transcription factors were found to be likely involved in tanshinone biosynthesis. Among these CYPs, 14 CYPs have been reported previously, and 11 CYPs were identified in this study. Expression analysis showed that four newly identified CYPs were upregulated upon application of MeJA, suggesting their possible roles in tanshinone biosynthesis. Overall, this study not only identified candidate genes involved in tanshinone biosynthesis but also provided a basis for characterization of genes involved in important active ingredients of other traditional Chinese medicinal plants.

Expanding the roles for 2-oxoglutarate-dependent oxygenases in plant metabolism

Covering: up to 2018 2-Oxoglutarate-dependent oxygenases (2ODOs) comprise a large enzyme superfamily in plant genomes, second in size only to the cytochromes P450 monooxygenase (CYP) superfamily. 2ODOs participate in both primary and specialized plant pathways, and their occurrence across all life kingdoms points to an ancient origin. Phylogenetic evidence supports substantial expansion and diversification of 2ODOs following the split from the common ancestor of land plants. More conserved roles for these enzymes include oxidation within hormone metabolism, such as the recently described capacity of Dioxygenase for Auxin Oxidation (DAO) for governing auxin homeostasis. Conserved structural features among 2ODOs has provided a basis for continued investigation into their mechanisms, and recent structural work is expected to illuminate intriguing reactions such as that of 1-aminocyclopropane-1-carboxylic acid oxidase (ACCO). Phylogenetic radiation among this superfamily combined with neo- and subfunctionalization has enabled recruitment to highly specialized pathways, including those yielding medicines, flavours, dyes, poisons, and compounds important for plant-environment interactions. Catalytic versatility of 2ODOs in plants and across broader taxa continues to inspire biochemists tasked with the discovery of new enzymes. This highlight article summarizes recent reports up to 2018 of 2ODOs within plant metabolism. Furthermore, the respective contributions of 2ODOs and other oxidases to natural product biosynthesis are discussed as a framework for continued discovery.

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.

The AP2/ERF transcription factor SmERF128 positively regulates diterpenoid biosynthesis in Salvia miltiorrhiza

The novel AP2/ERF transcription factor SmERF128 positively regulates diterpenoid tanshinone biosynthesis by activating the expression of SmCPS1, SmKSL1, and SmCYP76AH1 in Salvia miltiorrhiza. Certain members of the APETALA2/ethylene-responsive factor (AP2/ERF) family regulate plant secondary metabolism. Although it is clearly documented that AP2/ERF transcription factors (TFs) are involved in sesquiterpenoid biosynthesis, the regulation of diterpenoid biosynthesis by AP2/ERF TFs remains elusive. Here, we report that the novel AP2/ERF TF SmERF128 positively regulates diterpenoid tanshinone biosynthesis in Salvia miltiorrhiza. Overexpression of SmERF128 increased the expression levels of copalyl diphosphate synthase 1 (SmCPS1), kaurene synthase-like 1 (SmKSL1) and cytochrome P450 monooxygenase 76AH1 (SmCYP76AH1), whereas their expression levels were decreased when SmERF128 was silenced. Accordingly, the content of tanshinone was reduced in SmERF128 RNA interference (RNAi) hairy roots and dramatically increased in SmERF128 overexpression hairy roots, as demonstrated through Ultra Performance Liquid Chromatography (UPLC) and Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) analysis. Furthermore, SmERF128 activated the expression of SmCPS1, SmKSL1, and SmCYP76AH1 by binding to the GCC box, and to the CRTDREHVCBF2 (CBF2) and RAV1AAT (RAA) motifs within their promoters during in vivo and in vitro assays. Our findings not only reveal the molecular basis of how the AP2/ERF transcription factor SmERF128 regulates diterpenoid biosynthesis, but also provide useful information for improving tanshinone production through genetic engineering.

Proteomic analysis reveals novel insights into tanshinones biosynthesis in Salvia miltiorrhiza hairy roots

Salvia miltiorrhiza is a medicinal plant highly appreciated by its content of tanshinones and salvianolic acids. Tanshinones are of particular relevance for their anti-oxidant, anti-tumoral and anti-inflammatory properties. Abiotic and biotic agents as silver nitrate and yeast extract have shown efficiently to stimulate tanshinone accumulation, but the underlying molecular mechanism remains essentially unknown. By using hairy roots as experimental material and the elicitors mentioned, were obtained up to 22 mg of tanshinones per gram of dry weight. Differential label-free quantitative proteomic analysis was applied to study the proteins involved in tanshinone biosynthesis. A total of 2650 proteins were identified in roots extracts, of which 893 showed statistically (p < 0.05) significant change in relative abundance compared to control roots, 251 proteins were upregulated and 642 downregulated. Among the upregulated proteins the predominant functional categories were metabolism (47%), stress defense (18%) and redox homeostasis (10%). Within the metabolism category, isoprenoid metabolism enzymes, cytochromes P450 and FAD-binding berberine proteins showed abundance profile linked to tanshinone concentration. The results presented here allowed to propose 5 new cytochromes P450 and 5 berberine enzymes as candidates to be involved into tanshinone biosynthesis, a novel finding that opens new avenues to improve tanshinone production through biotechnological approaches.

The genome of the medicinal plant Andrographis paniculata provides insight into the biosynthesis of the bioactive diterpenoid neoandrographolide

Andrographis paniculata is a herbaceous dicot plant widely used for its anti-inflammatory and anti-viral properties across its distribution in China, India and other Southeast Asian countries. A. paniculata was used as a crucial therapeutic treatment during the influenza epidemic of 1919 in India, and is still used for the treatment of infectious disease in China. A. paniculata produces large quantities of the anti-inflammatory diterpenoid lactones andrographolide and neoandrographolide, and their analogs, which are touted to be the next generation of natural anti-inflammatory medicines for lung diseases, hepatitis, neurodegenerative disorders, autoimmune disorders and inflammatory skin diseases. Here, we report a chromosome-scale A. paniculata genome sequence of 269 Mb that was assembled by Illumina short reads, PacBio long reads and high-confidence (Hi-C) data. Gene annotation predicted 25 428 protein-coding genes. In order to decipher the genetic underpinning of diterpenoid biosynthesis, transcriptome data from seedlings elicited with methyl jasmonate were also obtained, which enabled the identification of genes encoding diterpenoid synthases, cytochrome P450 monooxygenases, 2-oxoglutarate-dependent dioxygenases and UDP-dependent glycosyltransferases potentially involved in diterpenoid lactone biosynthesis. We further carried out functional characterization of pairs of class-I and -II diterpene synthases, revealing the ability to produce diversified labdane-related diterpene scaffolds. In addition, a glycosyltransferase able to catalyze O-linked glucosylation of andrograpanin, yielding the major active product neoandrographolide, was also identified. Thus, our results demonstrate the utility of the combined genomic and transcriptomic data set generated here for the investigation of the production of the bioactive diterpenoid lactone constituents of the important medicinal herb A. paniculata.

Trends in herbgenomics

From Shen Nong's Herbal Classic (Shennong Bencao Jing) to the Compendium of Materia Medica (Bencao Gangmu) and the first scientific Nobel Prize for the mainland of China, each milestone in the historical process of the development of traditional Chinese medicine (TCM) involves screening, testing and integrating. After thousands of years of inheritance and development, herbgenomics (bencaogenomics) has bridged the gap between TCM and international advanced omics studies, promoting the application of frontier technologies in TCM. It is a discipline that uncovers the genetic information and regulatory networks of herbs to clarify their molecular mechanism in the prevention and treatment of human diseases. The main theoretical system includes genomics, functional genomics, proteomics, transcriptomics, metabolomics, epigenomics, metagenomics, synthetic biology, pharmacogenomics of TCM, and bioinformatics, among other fields. Herbgenomics is mainly applicable to the study of medicinal model plants, genomic-assisted breeding, herbal synthetic biology, protection and utilization of gene resources, TCM quality evaluation and control, and TCM drug development. Such studies will accelerate the application of cutting-edge technologies, revitalize herbal research, and strongly promote the development and modernization of TCM.

Diverse responses of tanshinone biosynthesis to biotic and abiotic elicitors in hairy root cultures of Salvia miltiorrhiza and Salvia castanea Diels f. tomentosa

Salvia miltiorrhiza (S. miltiorrhiza) and Salvia castanea Diels f. tomentosa (S. castanea) are both used for treatment of cardiovascular diseases. They have the same bioactive compound tanshinones, but whose contents are hugely different. This study illustrated diverse responses of tanshinone biosynthesis to yeast extract (YE) and Ag⁺ in hairy roots of the two species. YE enhanced both the growth and tanshinone biosynthesis of two hairy roots, and contributed more to tanshinone accumulation in S. castanea than that in S. miltiorrhiza. Genes encoding 1-deoxy-d-xylulose 5-phosphate synthase (DXS2), geranylgeranyl diphosphatesynthase (GGPPS1), copalyl diphosphate synthase (CPS1), and two cytochromes P450 (CYP76AH1 and CYP76AH3) were also more responsive to YE in S. castanea than those in S. miltiorrhiza. Accumulations of dihydrotanshinone I and tanshinone I, and most biosynthetic genes in S. miltiorrhiza were more responsive to Ag⁺ than those in S. castanea. Accumulations of dihydrotanshinone I and cryptotanshinone were more responsive to YE, while tanshinone IIA accumulation was more responsive to Ag⁺ in S. miltiorrhiza. However, accumulations of other four tanshinones and related genes in S. castanea were more responsive to YE than Ag⁺. This study provides foundations for studying diverse specialized metabolism between the related species.