MYB transcription factors and their role in Medicinal plants

Integrative analysis of the R2R3-MYB gene family revealed that BsMYB36 and BsMYB51 significantly regulate the accumulation of flavonoids in Bletilla striata (Orchidaceae)

The R2R3-MYB transcription factors constitute a critical family involved in a variety of biological processes. They have been found to be essential participants in flavonoid biosynthesis in various plants. Bletilla striata (Thunb.) Reichb. f. is an orchid species rich in flavonoid compounds, with anti-inflammatory and antioxidant properties. In this study, we identified 94 R2R3-MYB genes, 89 of them were classified into 22 subgroups, and 92 were mapped to 16 chromosomes. The S5 and S7 subfamilies contained three and four members, respectively which might play roles in the biosynthesis of anthocyanin, proanthocyanidin, and flavonoid. Additionally, BsR2R3-MYBs exhibited tissue-specific expression. There were 36 genes, and 35 genes exhibited high expression in roots and pseudobulbs, respectively. The 25 R2R3-MYB genes from different subfamilies showed varying responses to drought, low temperature, and MeJA treatments. Furthermore, the S5 subfamily member BsMYB51 and the S7 subfamily member BsMYB36 were heterologous expressed in A.thaliana. Phenotypic observations of A.thaliana showed that BsMYB36 and BsMYB51 could compensate for the growth differences caused by the atmyb12 and atmyb123 mutations, respectively. Moreover, the overexpression of BsMYB36 increased flavonoid content, while decreasing the accumulation of anthocyanin and proanthocyanidin in A.thaliana. The overexpression of BsMYB51 promoted the accumulation of flavonoid, anthocyanin, and proanthocyanidin. Overexpression of BsMYB36 and BsMYB51 significantly upregulated relative genes in the phenylpropanoid and flavonoid biosynthesis pathways, such as PAL, CHS, F3'H, and DFR. This study provids the foundation for exploring the regulation of flavonoid content by BsMYBs in B.striata.

Genome-wide identification and expression profiling of MYB transcription factors in Artemisia argyi

Artemisia argyi, a significant medicinal plant in China, is known for its high content of essential oils, flavonoids, and other bioactive compounds. MYB transcription factors are the largest gene family in plants and are widely reported to play important roles in plant development, metabolism, defense, and stress resistance. However, the MYB family of A. argyi has not been systematically studied. The aim of this study was to comprehensively analyze the MYB gene family of A. argyi and explore its potential role in flavonoid biosynthesis. Here, the phylogeny, chromosome location, gene structure, cis-acting elements, expression patterns and Gene ontology (GO) annotation of MYB gene family members were investigated using bioinformatics methods based on the whole-genome and transcriptome data of A. argyi. In total, 227 AYMYB transcription factors were identified from A. argyi genome, including 22 1R-MYB, 165 R2R3-MYB, 16 3R-MYB, 5 4R-MYB and 19 atypical MYB members. These AYMYBs were unevenly distributed across the A. argyi genome. Subcellular localization prediction revealed that all the AYMYBs were localized in the nucleus. The protein motifs, conserved domains, and gene structures of AYMYBs were identified, and the results showed that AYMYBs from the same subfamily exhibited similar motifs and gene structures. Cis-acting elements and GO analysis suggested that AYMYBs may be involved in many biological processes related to plant development, metabolism, defense, and stress resistance. Moreover, quantitative real-time PCR (qRT-PCR) analysis showed that approximately 50 genes showed high expression levels in the leaves of A. argyi and AYMYBs showed specific expression patterns under MeJA treatment. Together, our research will offer useful information for future investigations into the functions of MYB genes in A. argyi, especially in regulating the process of flavonoid biosynthesis in leaves and in response to MeJA treatment.

MYB polymorphism molecular marker: A novel molecular marker for authenticity and geographical origin identification of Citri Reticulatae Pericarpium

Objective

Citri Reticulatae Pericarpium (Chenpi, CRP) is one of the most used traditional Chinese medicines with great medicinal, dietary and collection values, among which the Citrus reticulata cv. 'Chachi' (Citrus reticulata cv. Chachiensis) from Guangdong Xinhui is the geoherb of CRP. Xinhui CRP in the market was often counterfeited with other varieties or origins, molecular identification method can effectively distinguish different CRP varieties, but it's still a difficult problem to identify the same CRP variety from different origin. It is necessary to discover a new molecular marker to ensure the safe and effective application of Xinhui CRP.

Methods

We selected one of the most studied transcription factor families in Citrus genus, MYB, to design the specific candidate primers on the conserved region. The primers with good band repeatability and high polymorphism were screened for PCR amplification of the test materials, and the genetic similarity coefficient among different families, genera, species, and origins were calculated. The cluster analysis was performed by unweighted pair group method using arithmetic average (UPGMA).

Results

A total of ten MYB primers were screened out to identify Xinhui CRP from plants from different family (Panax ginseng and Morus alba), genus (Clausena lansium and Zanthoxylum schinifolium), and species (Citrus reticulata, C. sinensis and C. maxima). Furthermore, two from the ten primers, M1 and M10, were found to distinguish Xinhui CRP from other origins. There were 169, 113, 133 and 134 polymorphic bands in the identification of different families, genera, species, and origins respectively, and the accordingly polymorphism ration were 79.88%, 76.87%, 79.20% and 82.84%. Moreover, M1 was discovered to be the best primer to identify Xinhui CRP from other seven origins, the cluster analysis results based on the genetic similarity coefficients were consistent with the geographical distribution.

Conclusion

This study established a novel molecular identification method according to MYB transcription factor, which can analyze the potential parental relationship of CRP germplasm, as well as identify the quality and origins of Xinhui CPR.

Transcription factor KUA1 positively regulates tomato resistance against Phytophthora infestans by fine-tuning reactive oxygen species accumulation

Tomato is a horticultural crop of global significance. However, the pathogen Phytophthora infestans causing the late blight disease imposes a severe threat to tomato production and quality. Many transcription factors (TFs) are known to be involved in responses to plant pathogens, however, the key TFs in tomato resistant to P. infestans remain to be explored. Here, we identified six TFs related to tomato responses to P. infestans infection. In particular, we found overexpression of SlKUA1 could significantly improve tomato resistance to P. infestans; moreover, reactive oxygen species (ROS) accumulation was significantly increased in OE-SlKUA1 compared with WT after P. infestans infection along with higher expression of SlRBOHD. Surprisingly, we found that SlKUA1 could not bind to the promoter of SlRBOHD. Further experiments revealed that SlKUA1 inhibited the expression of SlPrx1 by binding to its promoter region, thereby decreasing POD enzyme abundance and causing compromised ROS scavenge. Meanwhile, we identified that SlKUA1 also binds to the promoter region of two plant immune-related genes, SlMAPK7 and SlRLP4, promoting their expression and enhancing tomato disease resistance. Together, our results have unraveled that SlKUA1 can boost tomato resistance against P. infestans through quantitatively regulating ROS accumulation and related immune gene expression, thus, providing promising new targets for breeding late blight resistance tomatoes.

Identification and functional characterization of the MYB transcription factor GmMYBLJ in soybean leaf senescence

Leaf senescence is an important agronomic trait that significantly influences the quality and yield of soybeans. v-Myb avian myeloblastosis viral oncogene homolog (MYB) transcription factors are considered crucial regulators governing leaf senescence, which can be utilized to improve agronomic traits in crops. However, our knowledge regarding the functional roles of soybean MYBs in leaf senescence is extremely limited. In this study, GmMYBLJ, a CCA1-like MYB, was identified and functionally characterized with respect to leaf senescence. The GmMYBLJ protein is localized in the nucleus, and a high accumulation of its transcripts was observed in nodules and embryos. Notably, GmMYBLJ was highly expressed in soybean senescent leaves and was transcriptionally induced by dark or NaCl treatment, as confirmed by histochemical GUS staining analysis. Ectopic overexpression of GmMYBLJ in Arabidopsis not only led to earlier leaf senescence, reduced chlorophyll content, and increased MDA accumulation but also promoted the expression of several WRKY family transcription factors and senescence-associated genes, such as SAG12 and ORE1. Further investigation showed that overexpression of GmMYBLJ accelerated Arabidopsis leaf senescence under darkness and in response to Pst DC3000 infection. Moreover, transgenic soybean plants overexpressing GmMYBLJ grew faster and exhibited accelerated senescence under salt stress. DAB staining analysis showed that GmMYBLJ induced ROS accumulation in soybean hairy roots and Arabidopsis leaves. Collectively, our results provided useful information into the functional roles of GmMYBLJ in both age-dependent and stress-induced senescence.

Identification and expression profiling of microRNAs in leaf tissues of Foeniculum vulgare Mill. under salinity stress

Foeniculum vulgare Mill. commonly known as fennel, is a globally recognized aromatic medicinal plant and culinary herb with widespread popularity due to its antimicrobial, antioxidant, carminative, and diuretic properties, among others. Although the phenotypic effects of salinity stress have been previously explored in fennel, the molecular mechanisms underlying responses to elevated salinity in this plant remain elusive. MicroRNAs (miRNAs) are tiny, endogenous, and extensively conserved non-coding RNAs (ncRNAs) typically ranging from 20 to 24 nucleotides (nt) in length that play a major role in a myriad of biological functions. In fact, a number of miRNAs have been extensively associated with responses to abiotic stress in plants. Consequently, employing computational methodologies and rigorous filtering criteria, 40 putative miRNAs belonging to 25 different families were characterized from fennel in this study. Subsequently, employing the psRNATarget tool, a total of 67 different candidate target transcripts for the characterized fennel miRNAs were predicted. Additionally, the expression patterns of six selected fennel miRNAs (i.e. fvu-miR156a, fvu-miR162a-3p, fvu-miR166a-3p, fvu-miR167a-5p, fvu-miR171a-3p, and fvu-miR408-3p) were analyzed under salinity stress conditions via qPCR. This article holds notable significance as it identifies not only 40 putative miRNAs in fennel, a non-model plant, but also pioneers the analysis of their expression under salinity stress conditions.

Transcriptome-based analysis of key functional genes in the triterpenoid saponin synthesis pathway of Platycodon grandiflorum

BACKGROUND

Platycodon grandiflorum (P. grandiflorum) is a commonly used medicinal plant in China. Transcriptome sequencing studies of different tissues of P. grandiflorum have been widely conducted. However, studies on transcriptome sequencing and expression patterns of key genes in the saponin synthesis pathway of Tongcheng P. grandiflorum, a high-quality medicinal resource of different years, are relatively limited.

RESULTS

This study involved transcriptome sequencing and bioinformatics analysis of the roots from annual, biennial, and triennial P. grandiflorum in the Tongcheng area. After data filtering and assembly, we obtained 111.44 Gb of clean base data, including 742,880616 clean reads. We identified 5,156 differential expression unigenes between at least two sample groups, with differences noted among annual, biennial, and triennial P. grandiflorum plants. GO enrichment analysis annotated 3509, 1819, and 1393 DEGs in comparison TC1vsTC2, TC1vsTC3, and TC2vsTC3, respectively. Furthermore, KEGG enrichment analysis identified 16 genes encoding key enzymes in the terpene skeleton biosynthesis, sesquiterpene and triterpene biosynthesis pathways, including SE, AACT, FPPS, DXR, HMGR, HMGS, and DXS. The results of qRT-PCR experiments showed that most of the genes were most highly expressed in annual P. grandiflorum.

CONCLUSIONS

The present study provided transcriptomic data from the roots of Tongcheng P. grandiflorum of different years, which provides critical bioinformatics data on the growth and development of P. grandiflorum, laying a foundation for further research on saponins and identifying key enzymes involved in this process across different growth stages.

Comparative and functional analysis unveils the contribution of photoperiod to DNA methylation, sRNA accumulation, and gene expression variations in short-day and long-day grasses

Photoperiod employs complicated networks to regulate various developmental processes in plants, including flowering transition. However, the specific mechanisms by which photoperiod affects epigenetic modifications and gene expression variations in plants remain elusive. In this study, we conducted a comprehensive analysis of DNA methylation, small RNA (sRNA) accumulation, and gene expressions under different daylengths in facultative long-day (LD) grass Brachypodium distachyon and short-day (SD) grass rice. Our results showed that while overall DNA methylation levels were minimally affected by different photoperiods, CHH methylation levels were repressed under their favorable light conditions, particularly in rice. We identified numerous differentially methylated regions (DMRs) that were influenced by photoperiod in both plant species. Apart from differential sRNA clusters, we observed alterations in the expression of key components of the RNA-directed DNA methylation pathway, DNA methyltransferases, and demethylases, which may contribute to the identified photoperiod-influenced CHH DMRs. Furthermore, we identified many differentially expressed genes in response to different daylengths, some of which were associated with the DMRs. Notably, we discovered a photoperiod-responsive gene MYB11 in the transcriptome of B. distachyon, and further demonstrated its role as a flowering inhibitor by repressing FT1 transcription. Together, our comparative and functional analysis sheds light on the effects of daylength on DNA methylation, sRNA accumulation, and gene expression variations in LD and SD plants, thereby facilitating better designing breeding programs aimed at developing high-yield crops that can adapt to local growing seasons.

Effects of MhMYB1 and MhMYB2 transcription factors on the monoterpenoid biosynthesis pathway in l-menthol chemotype of Mentha haplocalyx Briq

MAIN CONCLUSION

Transcription factors MhMYB1 and MhMYB2 correlate with monoterpenoid biosynthesis pathway in l-menthol chemotype of Mentha haplocalyx Briq, which could affect the contents of ( -)-menthol and ( -)-menthone. Mentha haplocalyx Briq., a plant with traditional medicinal and edible uses, is renowned for its rich essential oil content. The distinct functional activities and aromatic flavors of mint essential oils arise from various chemotypes. While the biosynthetic pathways of the main monoterpenes in mint are well understood, the regulatory mechanisms governing different chemotypes remain inadequately explored. In this investigation, we identified and cloned two transcription factor genes from the M. haplocalyx MYB family, namely MhMYB1 (PP236792) and MhMYB2 (PP236793), previously identified by our research group. Bioinformatics analysis revealed that MhMYB1 possesses two conserved MYB domains, while MhMYB2 contains a conserved SANT domain. Yeast one-hybrid (Y1H) analysis results demonstrated that both MhMYB1 and MhMYB2 interacted with the promoter regions of MhMD and MhPR, critical enzymes in the monoterpenoid biosynthesis pathway of M. haplocalyx. Subsequent virus-induced gene silencing (VIGS) of MhMYB1 and MhMYB2 led to a significant reduction (P < 0.01) in the relative expression levels of MhMD and MhPR genes in the VIGS groups of M. haplocalyx. In addition, there was a noteworthy decrease (P < 0.05) in the contents of ( -)-menthol and ( -)-menthone in the essential oil of M. haplocalyx. These findings suggest that MhMYB1 and MhMYB2 transcription factors play a positive regulatory role in ( -)-menthol biosynthesis, consequently influencing the essential oil composition in the l-menthol chemotype of M. haplocalyx. This study serves as a pivotal foundation for unraveling the regulatory mechanisms governing monoterpenoid biosynthesis in different chemotypes of M. haplocalyx.

Characteristics and Functions of MYB (v-Myb avivan myoblastsis virus oncogene homolog)-Related Genes in Arabidopsis thaliana

The MYB (v-Myb avivan myoblastsis virus oncogene homolog) transcription factor family is one of the largest families of plant transcription factors which plays a vital role in many aspects of plant growth and development. MYB-related is a subclass of the MYB family. Fifty-nine Arabidopsis thaliana MYB-related (AtMYB-related) genes have been identified. In order to understand the functions of these genes, in this review, the promoters of AtMYB-related genes were analyzed by means of bioinformatics, and the progress of research into the functions of these genes has been described. The main functions of these AtMYB-related genes are light response and circadian rhythm regulation, root hair and trichome development, telomere DNA binding, and hormone response. From an analysis of cis-acting elements, it was found that the promoters of these genes contained light-responsive elements and plant hormone response elements. Most genes contained elements related to drought, low temperature, and defense and stress responses. These analyses suggest that AtMYB-related genes may be involved in A. thaliana growth and development, and environmental adaptation through plant hormone pathways. However, the functions of many genes do not occur independently but instead interact with each other through different pathways. In the future, the study of the role of the gene in different pathways will be conducive to a comprehensive understanding of the function of the gene. Therefore, gene cloning and protein functional analyses can be subsequently used to understand the regulatory mechanisms of AtMYB-related genes in the interaction of multiple signal pathways. This review provides theoretical guidance for the follow-up study of plant MYB-related genes.

Downregulation of a transcription factor associated with resistance to Bt toxin Vip3Aa in the invasive fall armyworm

Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have revolutionized control of some major pests. However, more than 25 cases of field-evolved practical resistance have reduced the efficacy of transgenic crops producing crystalline (Cry) Bt proteins, spurring adoption of alternatives including crops producing the Bt vegetative insecticidal protein Vip3Aa. Although practical resistance to Vip3Aa has not been reported yet, better understanding of the genetic basis of resistance to Vip3Aa is urgently needed to proactively monitor, delay, and counter pest resistance. This is especially important for fall armyworm (Spodoptera frugiperda), which has evolved practical resistance to Cry proteins and is one of the world's most damaging pests. Here, we report the identification of an association between downregulation of the transcription factor gene SfMyb and resistance to Vip3Aa in S. frugiperda. Results from a genome-wide association study, fine-scale mapping, and RNA-Seq identified this gene as a compelling candidate for contributing to the 206-fold resistance to Vip3Aa in a laboratory-selected strain. Experimental reduction of SfMyb expression in a susceptible strain using RNA interference (RNAi) or CRISPR/Cas9 gene editing decreased susceptibility to Vip3Aa, confirming that reduced expression of this gene can cause resistance to Vip3Aa. Relative to the wild-type promoter for SfMyb, the promoter in the resistant strain has deletions and lower activity. Data from yeast one-hybrid assays, genomics, RNA-Seq, RNAi, and proteomics identified genes that are strong candidates for mediating the effects of SfMyb on Vip3Aa resistance. The results reported here may facilitate progress in understanding and managing pest resistance to Vip3Aa.

Multilayered regulation of secondary metabolism in medicinal plants

Medicinal plants represent a huge reservoir of secondary metabolites (SMs), substances with significant pharmaceutical and industrial potential. However, obtaining secondary metabolites remains a challenge due to their low-yield accumulation in medicinal plants; moreover, these secondary metabolites are produced through tightly coordinated pathways involving many spatiotemporally and environmentally regulated steps. The first regulatory layer involves a complex network of transcription factors; a second, more recently discovered layer of complexity in the regulation of SMs is epigenetic modification, such as DNA methylation, histone modification and small RNA-based mechanisms, which can jointly or separately influence secondary metabolites by regulating gene expression. Here, we summarize the findings in the fields of genetic and epigenetic regulation with a special emphasis on SMs in medicinal plants, providing a new perspective on the multiple layers of regulation of gene expression.

Genome-Wide Identification of the MYB and bHLH Families in Carnations and Expression Analysis at Different Floral Development Stages

Carnations are one of the most popular ornamental flowers in the world with varied flower colors that have long attracted breeders and consumers alike. The differences in carnation flower color are mainly the result of the accumulation of flavonoid compounds in the petals. Anthocyanins are a type of flavonoid compound that produce richer colors. The expression of anthocyanin biosynthetic genes is mainly regulated by MYB and bHLH transcription factors. However, these TFs have not been comprehensively reported in popular carnation cultivars. Herein, 106 MYB and 125 bHLH genes were identified in the carnation genome. Gene structure and protein motif analyses show that members of the same subgroup have similar exon/intron and motif organization. Phylogenetic analysis combining the MYB and bHLH TFs from Arabidopsis thaliana separates the carnation DcaMYBs and DcabHLHs into 20 subgroups each. Gene expression (RNAseq) and phylogenetic analysis shows that DcaMYB13 in subgroup S4 and DcabHLH125 in subgroup IIIf have similar expression patterns to those of DFR, ANS, and GT/AT, which regulate anthocyanin accumulation, in the coloring of carnations, and in red-flowered and white-flowered carnations, DcaMYB13 and DcabHLH125 are likely the key genes responsible for the formation of red petals in carnations. These results lay a foundation for the study of MYB and bHLH TFs in carnations and provide valuable information for the functional verification of these genes in studies of tissue-specific regulation of anthocyanin biosynthesis.