The grapevine R2R3-MYB transcription factor VvMYBF1 regulates flavonol synthesis in developing grape berries

Combinatorial Regulation of Stilbene Synthase Genes by WRKY and MYB Transcription Factors in Grapevine (Vitis vinifera L.)

Stilbene synthase (STS) is the key enzyme leading to the biosynthesis of resveratrol. Recently we reported two R2R3-MYB transcription factor (TF) genes that regulate the stilbene biosynthetic pathway in grapevine: VviMYB14 and VviMYB15. These genes are strongly co-expressed with STS genes under a range of stress and developmental conditions, in agreement with the specific activation of STS promoters by these TFs. Genome-wide gene co-expression analysis using two separate transcriptome compendia based on microarray and RNA sequencing data revealed that WRKY TFs were the top TF family correlated with STS genes. On the basis of correlation frequency, four WRKY genes, namely VviWRKY03, VviWRKY24, VviWRKY43 and VviWRKY53, were further shortlisted and functionally validated. Expression analyses under both unstressed and stressed conditions, together with promoter-luciferase reporter assays, suggested different hierarchies for these TFs in the regulation of the stilbene biosynthetic pathway. In particular, VviWRKY24 seems to act as a singular effector in the activation of the VviSTS29 promoter, while VviWRKY03 acts through a combinatorial effect with VviMYB14, suggesting that these two regulators may interact at the protein level as previously reported in other species.

Grape Berry Acclimation to Excessive Solar Irradiance Leads to Repartitioning between Major Flavonoid Groups

Warm viticulture regions are associated with inferior wines, resulting from the interaction between microclimate and fruit biochemistry. Solar irradiance triggers biosynthetic processes in the fruit and dominates its thermal balance. Therefore, deciphering its impact on fruit metabolism is pivotal to develop strategies for fruit protection and ameliorate its quality traits. Here, we modified light quality and intensity in the fruit-zone and integrated micrometeorology with grape and wine metabolomics, allowing a complete assessment, from field to bottle. We analyzed the dynamics of fruit's adaptation to altered conditions during ripening and constructed temporal-based metabolic networks. Micrometeorological modifications shifted the balance between the major flavonoids, associating increased solar exposure with lower levels of anthocyanins and flavan-3-ols, and higher flavonols. Differences were fixed from 2 weeks postveraison until harvest, suggesting a controlled acclimation response rather than external modulation. Differences in grape composition manifested in the wine and resulted in higher color intensity and improved wine hue under partial shading.

The R2R3 transcription factor HlMYB8 and its role in flavonoid biosynthesis in hop (Humulus lupulus L.)

Hop is an important source of medicinally valuable secondary metabolites including bioactive prenylated chalcones. To gain in-depth knowledge of the regulatory mechanisms of hop flavonoids biosynthesis, full-length cDNA of HlMyb8 transcription factor gene was isolated from lupulin glands. The deduced amino acid sequence of HlMyb8 showed high similarity to a flavonol-specific regulator of phenylpropanoid biosynthesis AtMYB12 from Arabidopsis thaliana. Transient expression studies and qRT-PCR analysis of transgenic hop plants overexpressing HlMyb8 revealed that HlMYB8 activates expression of chalcone synthase HlCHS_H1 as well as other structural genes from the flavonoid pathway branch leading to the production of flavonols (F3H, F'3H, FLS) but not prenylflavonoids (PT1, OMT1) or bitter acids (VPS, PT1). HlMyb8 could cross-activate Arabidopsis flavonol-specific genes but to a much lesser extent than AtMyb12. Reciprocally, AtMyb12 could cross-activate hop flavonol-specific genes. Transcriptome sequence analysis of hop leaf tissue overexpressing HlMyb8 confirmed the modulation of several other genes related to flavonoid biosynthesis pathways (PAL, 4CL, ANR, DFR, LDOX). Analysis of metabolites in hop female cones confirmed that overexpression of HlMyb8 does not increase prenylflavonoid or bitter acids content in lupulin glands. It follows from our results that HlMYB8 plays role in a competition between flavonol and prenylflavonoid or bitter acid pathways by diverting the flux of CHS_H1 gene product and thus, may influence the level of these metabolites in hop lupulin.

Transcriptome Analysis Reveals Molecular Signatures of Luteoloside Accumulation in Senescing Leaves of Lonicera macranthoides

Lonicera macranthoides is an important medicinal plant widely used in traditional Chinese medicine. Luteoloside is a critical bioactive compound in L. macranthoides. To date, the molecular mechanisms underlying luteoloside biosynthesis are still largely unknown. In this work, high performance liquid chromatography (HPLC) was employed to determine the luteoloside contents in leaves, stems, and flowers at different developmental stages. Results showed that senescing leaves can accumulate large amounts of luteoloside, extremely higher than that in young and semi-lignified leaves and other tissues. RNA-Seq analysis identified that twenty-four differentially expressed unigenes (DEGs) associated with luteoloside biosynthesis were significantly up-regulated in senescing leaves, which are positively correlated with luteoloside accumulation. These DEGs include phenylalanine ammonia lyase 2, cinnamate 4-hydroxylase 2, thirteen 4-coumarate-CoA ligases, chalcone synthase 2, six flavonoid 3'-monooxygenase (F3'H) and two flavone 7-O-β-glucosyltransferase (UFGT) genes. Further analysis demonstrated that two F3'Hs (CL11828.Contig1 and CL11828.Contig2) and two UFGTs (Unigene2918 and Unigene97915) might play vital roles in luteoloside generation. Furthermore, several transcription factors (TFs) related to flavonoid biosynthesis including MYB, bHLH and WD40, were differentially expressed during leaf senescence. Among these TFs, MYB12, MYB75, bHLH113 and TTG1 were considered to be key factors involved in the regulation of luteoloside biosynthesis. These findings provide insights for elucidating the molecular signatures of luteoloside accumulation in L. macranthoides.

Solar UV light regulates flavonoid metabolism in apple (Malus x domestica)

Ultraviolet-B light (UV-B) is one environmental signal perceived by plants that affects the flavonoid pathway and influences the levels of anthocyanins, flavonols, and proanthocyanidins. To understand the mechanisms underlying UV exposure, apple trees were grown under spectral filters that altered transmission of solar UV light. Fruit analysis showed that UV induced changes in physiology, metabolism, and gene expression levels during development over a season. These changes were sustained after storage. Under low UV, ripening was delayed, fruit size decreased, and anthocyanin and flavonols were reduced. Expression analysis showed changes in response to UV light levels for genes in the regulation and biosynthesis of anthocyanin and flavonols. Transcription of flavonol synthase (FLS), ELONGATED HYPOCOTYL 5 (HY5), MYB10, and MYB22 were down-regulated throughout fruit development under reduced UV. Functional testing showed that the FLS promoter was activated by HY5, and this response was enhanced by the presence of MYB22. The MYB22 promoter can also be activated by the anthocyanin regulator, MYB10. As ambient levels of UV light vary around the globe, this study has implications for future crop production, the quality of which can be determined by the response to UV.

Isolation and Characterization of the Flavonol Regulator CcMYB12 From the Globe Artichoke [Cynara cardunculus var. scolymus (L.) Fiori]

Flavonoids are a well-studied group of secondary metabolites, belonging to the phenylpropanoid pathway. Flavonoids are known to exhibit health promoting effects such as antioxidant capacities, anti-cancer and anti-inflammatory activity. Globe artichoke is an important source of bioactive phenolic compounds, including flavonoids. To study the regulation of their biosynthesis, a R2R3-MYB transcription factor, CcMYB12, was isolated from artichoke leaves. Phylogenetic analysis showed that this protein belongs to the MYB subgroup 7 (flavonol-specific MYB), which includes Arabidopsis AtMYB12, grapevine VvMYBF1, and tomato SlMYB12. CcMYB12 transcripts were detected specifically in artichoke immature inflorescence and young leaves and overlapped with the profiles of flavonol biosynthetic genes. Electrophoretic mobility shift assays (EMSAs) revealed that recombinant CcMYB12 protein is able to bind to ACII element, a DNA binding site ubiquitously present in the promoters of genes encoding flavonol biosynthetic enzymes. In transgenic Arabidopsis plants, the overexpression of CcMYB12 activated the expression of endogenous flavonol biosynthesis genes, leading to an increase of flavonol accumulation and a decrease of anthocyanins in leaves. Likewise, in transgenic tobacco petals and leaves, the overexpression of CcMYB12 decreased anthocyanin levels and increased flavonols.

TRANSPARENT TESTA GLABRA 1-Dependent Regulation of Flavonoid Biosynthesis

The flavonoid composition of various tissues throughout plant development is of biological relevance and particular interest for breeding. Arabidopsis thaliana TRANSPARENT TESTA GLABRA 1 (AtTTG1) is an essential regulator of late structural genes in flavonoid biosynthesis. Here, we provide a review of the regulation of the pathway's core enzymes through AtTTG1-containing R2R3-MYELOBLASTOSIS-basic HELIX-LOOP-HELIX-WD40 repeat (MBW(AtTTG1)) complexes embedded in an evolutionary context. We present a comprehensive collection of A. thalianattg1 mutants and AtTTG1 orthologs. A plethora of MBW(AtTTG1) mechanisms in regulating the five major TTG1-dependent traits is highlighted.

The Tartary Buckwheat Genome Provides Insights into Rutin Biosynthesis and Abiotic Stress Tolerance

Tartary buckwheat (Fagopyrum tataricum) is an important pseudocereal crop that is strongly adapted to growth in adverse environments. Its gluten-free grain contains complete proteins with a well-balanced composition of essential amino acids and is a rich source of beneficial phytochemicals that provide significant health benefits. Here, we report a high-quality, chromosome-scale Tartary buckwheat genome sequence of 489.3 Mb that is assembled by combining whole-genome shotgun sequencing of both Illumina short reads and single-molecule real-time long reads, sequence tags of a large DNA insert fosmid library, Hi-C sequencing data, and BioNano genome maps. We annotated 33 366 high-confidence protein-coding genes based on expression evidence. Comparisons of the intra-genome with the sugar beet genome revealed an independent whole-genome duplication that occurred in the buckwheat lineage after they diverged from the common ancestor, which was not shared with rosids or asterids. The reference genome facilitated the identification of many new genes predicted to be involved in rutin biosynthesis and regulation, aluminum stress resistance, and in drought and cold stress responses. Our data suggest that Tartary buckwheat's ability to tolerate high levels of abiotic stress is attributed to the expansion of several gene families involved in signal transduction, gene regulation, and membrane transport. The availability of these genomic resources will facilitate the discovery of agronomically and nutritionally important genes and genetic improvement of Tartary buckwheat.

Characterization and functional analysis of a MYB gene (GbMYBFL) related to flavonoid accumulation in Ginkgo biloba

Flavonoids are a group of metabolites in Ginkgo biloba thought to provide health benefits. R2R3-MYB transcription factors (TFs) play key roles in the transcriptional regulation of the flavonoid biosynthesis in plants. In this study, an R2R3-MYB transcription factor gene, GbMYBFL, was isolated from G. biloba and characterized. Results of bioinformatic analysis indicated that GbMYBFL is more closely related to the R2R3-MYB involved in flavonoid biosynthesis and displayed high similarity to MYB from other plants. The genmomic sequence of GbMYBFL had three exons and two introns, with its upstream sequence containing cis-acting regulatory elements Myb binding site, Myc recognition sites, and light, SA, MeJA responsive elements. Subcellular localization analysis indicates that GbMYBFL was located in the nucleus. Quantitative real-time PCR revealed that GbMYBFL was expressed in leaves, stems, roots, young fruits, male flower and female flower, and the level of transcription in male flower and leaves were higher than that in female flower, stems, roots, and young fruits. During G. biloba leaf growth, the transcription of GbMYBFL is positively correlated with the flavonoid content, suggesting that the GbMYBFL is involved in the flavonoid biosynthesis. Overexpression of GbMYBFL under the control of the CaMV35S promoter in Ginkgo callus notably enhanced the accumulation of flavonoids and anthocyanin compared with non-transformed callus. This finding suggested that GbMYBFL positively related to flavonoid biosynthesis, and the overexpression of GbMYBFL was sufficient to induce flavonoids and anthocyanin accumulation.

PbrMYB21, a novel MYB protein of Pyrus betulaefolia, functions in drought tolerance and modulates polyamine levels by regulating arginine decarboxylase gene

MYB comprises a large family of transcription factors that play significant roles in plant development and stress response in plants. However, knowledge concerning the functions of MYBs and the target genes remains poorly understood. Here, we report the identification and functional characterization of a novel stress-responsive MYB gene from Pyrus betulaefolia. The MYB gene, designated as PbrMYB21, belongs to the R2R3-type and shares high degree of sequence similarity to MdMYB21. The transcript levels of PbrMYB21 were up-regulated under various abiotic stresses, particularly dehydration. PbrMYB21 was localized in the nucleus with transactivation activity. Overexpression of PbrMYB21 in tobacco conferred enhanced tolerance to dehydration and drought stresses, whereas down-regulation of PbrMYB21 in Pyrus betulaefolia by virus-induced gene silencing (VIGS) resulted in elevated drought sensitivity. Transgenic tobacco exhibited higher expression levels of ADC (arginine decarboxylase) and accumulated larger amount of polyamine in comparison with wild type (WT). VIGS of PbrMYB21 in Pyrus betulaefolia down-regulated ADC abundance and decreased polyamine level, accompanied by compromised drought tolerance. The promoter region of PbrADC contains one MYB-recognizing cis-element, which was shown to be interacted with PbrMYB21, indicating the ADC may be a target gene of PbrMYB21. Take together, these results demonstrated that PbrMYB21 plays a positive role in drought tolerance, which may be, at least in part, due to the modulation of polyamine synthesis by regulating the ADC expression.

Understanding the molecular mechanisms underlying the effects of light intensity on flavonoid production by RNA-seq analysis in Epimedium pseudowushanense B.L.Guo

Epimedium pseudowushanense B.L.Guo, a light-demanding shade herb, is used in traditional medicine to increase libido and strengthen muscles and bones. The recognition of the health benefits of Epimedium has increased its market demand. However, its resource recycling rate is low and environmentally dependent. Furthermore, its natural sources are endangered, further increasing prices. Commercial culture can address resource constraints of it.Understanding the effects of environmental factors on the production of its active components would improve the technology for cultivation and germplasm conservation. Here, we studied the effects of light intensities on the flavonoid production and revealed the molecular mechanism using RNA-seq analysis. Plants were exposed to five levels of light intensity through the periods of germination to flowering, the flavonoid contents were measured using HPLC. Quantification of epimedin A, epimedin B, epimedin C, and icariin showed that the flavonoid contents varied with different light intensity levels. And the largest amount of epimedin C was produced at light intensity level 4 (I4). Next, the leaves under the treatment of three light intensity levels ("L", "M" and "H") with the largest differences in the flavonoid content, were subjected to RNA-seq analysis. Transcriptome reconstruction identified 43,657 unigenes. All unigene sequences were annotated by searching against the Nr, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. In total, 4008, 5260, and 3591 significant differentially expressed genes (DEGs) were identified between the groups L vs. M, M vs. H and L vs. H. Particularly, twenty-one full-length genes involved in flavonoid biosynthesis were identified. The expression levels of the flavonol synthase, chalcone synthase genes were strongly associated with light-induced flavonoid abundance with the highest expression levels found in the H group. Furthermore, 65 transcription factors, including 31 FAR1, 17 MYB-related, 12 bHLH, and 5 WRKY, were differentially expressed after light induction. Finally, a model was proposed to explain the light-induced flavonoid production. This study provided valuable information to improve cultivation practices and produced the first comprehensive resource for E. pseudowushanense transcriptomes.

PtrMYB57 contributes to the negative regulation of anthocyanin and proanthocyanidin biosynthesis in poplar

A novel R2R3 MYB transcription factor PtrMYB57 interacted with bHLH131 and PtrTTG1 to form the MBW complex and negatively regulated the biosynthesis of both anthocyanins and PAs in poplar. R2R3-MYB transcription factors (TFs) are important regulators of secondary metabolite biosynthesis in woody species. A series of R2R3-MYB TFs involved in anthocyanin and proanthocyanidin (PA) biosynthesis have been identified in poplar. In this study, we report the identification and characterization of a subgroup 4 MYB member PtrMYB57, which contains a repressor domain (LxLxL) at the C-terminal end. PtrMYB57 encodes an R2R3 MYB protein localized in the nucleus and is predominantly expressed in mature leaves. Transgenic poplar overexpressing PtrMYB57 showed a reduction in anthocyanin and PA accumulation compared to wild-type plants. By contrast, a high anthocyanin and PA phenotype was observed in Ptrmyb57 mutants generated by the CRISPR/Cas9 system. Furthermore, transient expression assays revealed that PtrMYB57 interacted with bHLH131 (bHLH) and PtrTTG1 (WDR) to form the MBW complex and bound to the flavonoid gene promoters, leading to inhibition of these promoters. Taken together, our results suggest that PtrMYB57 plays a negative role in the regulation of anthocyanin and PA biosynthesis in poplar.

Genome-wide identification, functional prediction, and evolutionary analysis of the R2R3-MYB superfamily in Brassica napus

R2R3-MYB transcription factors (TFs) have been shown to play important roles in plants, including in development and in various stress conditions. Phylogenetic analysis showed the presence of 249 R2R3-MYB TFs in Brassica napus, called BnaR2R3-MYB TFs, clustered into 38 clades. BnaR2R3-MYB TFs were distributed on 19 chromosomes of B. napus. Sixteen gene clusters were identified. BnaR2R3-MYB TFs were characterized by motif prediction, gene structure analysis, and gene ontology. Evolutionary analysis revealed that BnaR2R3-MYB TFs are mainly formed as a result of whole-genome duplication. Orthologs and paralogs of BnaR2R3-MYB TFs were identified in B. napus, B. rapa, B. oleracea, and Arabidopsis thaliana using synteny-based methods. Purifying selection was pervasive within R2R3-MYB TFs. K_n/K_s values lower than 0.3 indicated that BnaR2R3-MYB TFs are being functionally converged. The role of gene conversion in the formation of BnaR2R3-MYB TFs was significant. Cis-regulatory elements in the upstream regions of BnaR2R3-MYB genes, miRNA targeting BnaR2R3MYB TFs, and post translational modifications were identified. Digital expression data revealed that BnaR2R3-MYB genes were highly expressed in the roots and under high salinity treatment after 24 h. BnaMYB21, BnaMYB141, and BnaMYB148 have been suggested for improving salt-tolerant B. napus. BnaR2R3-MYB genes were mostly up regulated on the 14th day post inoculation with Leptosphaeria biglobosa and L. maculan. BnaMYB150 is a candidate for increased tolerance to Leptospheria in B. napus.

A transcriptome analysis of two grapevine populations segregating for tendril phyllotaxy

The shoot structure of cultivated grapevine Vitis vinifera L. typically exhibits a three-node modular repetitive pattern, two sequential leaf-opposed tendrils followed by a tendril-free node. In this study, we investigated the molecular basis of this pattern by characterizing differentially expressed genes in 10 bulk samples of young tendril tissue from two grapevine populations showing segregation of mutant or wild-type shoot/tendril phyllotaxy. One population was the selfed progeny and the other one, an outcrossed progeny of a Vitis hybrid, 'Roger's Red'. We analyzed 13 375 expressed genes and carried out in-depth analyses of 324 of them, which were differentially expressed with a minimum of 1.5-fold changes between the mutant and wild-type bulk samples in both selfed and cross populations. A significant portion of these genes were direct cis-binding targets of 14 transcription factor families that were themselves differentially expressed. Network-based dependency analysis further revealed that most of the significantly rewired connections among the 10 most connected hub genes involved at least one transcription factor. TCP3 and MYB12, which were known important for plant-form development, were among these transcription factors. More importantly, TCP3 and MYB12 were found in this study to be involved in regulating the lignin gene PRX52, which is important to plant-form development. A further support evidence for the roles of TCP3-MYB12-PRX52 in contributing to tendril phyllotaxy was the findings of two other lignin-related genes uniquely expressed in the mutant phyllotaxy background.

SmMYB36, a Novel R2R3-MYB Transcription Factor, Enhances Tanshinone Accumulation and Decreases Phenolic Acid Content in Salvia miltiorrhiza Hairy Roots

Phenolic acids and tanshinones are two major bioactive components in Salvia miltiorrhiza Bunge. A novel endogenous R2R3-MYB transcription factor, SmMYB36, was identified in this research. This transcript factor can simultaneously influence the content of two types of components in SmMYB36 overexpression hairy roots. SmMYB36 was mainly localized in the nucleus of onion epidermis and it has transactivation activity. The overexpression of SmMYB36 promoted tanshinone accumulation but inhibited phenolic acid and flavonoid biosynthesis in Salvia miltiorrhiza hairy roots. The altered metabolite content was due to changed metabolic flow which was regulated by transcript expression of metabolic pathway genes. The gene transcription levels of the phenylpropanoid general pathway, tyrosine derived pathway, methylerythritol phosphate pathway and downstream tanshinone biosynthetic pathway changed significantly due to the overexpression of SmMYB36. The wide distribution of MYB binding elements (MBS, MRE, MBSI and MBSII) and electrophoretic mobility shift assay results indicated that SmMYB36 may be an effective tool to regulate metabolic flux shifts.

Chicory R2R3-MYB transcription factors CiMYB5 and CiMYB3 regulate fructan 1-exohydrolase expression in response to abiotic stress and hormonal cues

In the biennial Cichorium intybus, inulin-type fructans accumulate in the taproot during the first year. Upon cold or drought exposure, fructans are degraded by fructan exohydrolases, affecting inulin yield and degree of polymerization. While stress-induced expression of 1-FEH genes has been thoroughly explored, the transcriptional network mediating these responses has remained unknown. In this study, several R2R3-MYB transcriptional regulators were analysed for their possible involvement in 1-FEH regulation via transient transactivation of 1-FEH target promoters and for in vivo co-expression with target genes under different stress and hormone treatments. CiMYB3 and CiMYB5 selectively enhanced promoter activities of 1-FEH1, 1-FEH2a, and 1-FEH2b genes, without affecting promoter activities of fructosyltransferase genes. Both factors recognized the MYB-core motifs (C/TNGTTA/G) that are abundantly present in 1-FEH promoters. In chicory hairy root cultures, CiMYB5 displayed co-expression with its target genes in response to different abiotic stress and phytohormone treatments, whereas correlations with CiMYB3 expression were less consistent. Oligofructan levels indicated that the metabolic response, while depending on the balance of the relative expression levels of fructan exohydrolases and fructosyltransferases, could be also affected by differential subcellular localization of different FEH isoforms. The results indicate that in chicory hairy root cultures CiMYB5 and CiMYB3 act as positive regulators of the fructan degradation pathway.

A group of grapevine MYBA transcription factors located in chromosome 14 control anthocyanin synthesis in vegetative organs with different specificities compared with the berry color locus

Grapevine organs accumulate anthocyanins in a cultivar-specific and environmentally induced manner. The MYBA1-A2 genes within the berry color locus in chromosome 2 represent the major genetic determinants of fruit color. The simultaneous occurrence of transposon insertions and point mutations in these genes is responsible for most white-skinned phenotypes; however, the red pigmentation found in vegetative organs suggests the presence of additional regulators. This work describes a genomic region of chromosome 14 containing three closely related R2R3-MYB genes, named MYBA5, MYBA6 and MYBA7. Ectopic expression of the latter two genes in grapevine hairy roots promoted anthocyanin accumulation without affecting other phenylpropanoids. Transcriptomic profiling of hairy roots expressing MYBA1, MYBA6 and MYBA7 showed that these regulators share the activation of late biosynthetic and modification/transport-related genes, but differ in the activation of the FLAVONOID-3'5'-HYDROXYLASE (F3'5'H) family. An alternatively spliced MYBA6 variant was incapable of activating anthocyanin synthesis, however, because of the lack of an MYC1 interaction domain. MYBA1, MYBA6.1 and MYBA7 activated the promoters of UDP-GLUCOSE:FLAVONOID 3-O-GLUCOSYLTRANSFERASE (UFGT) and ANTHOCYANIN 3-O-GLUCOSIDE-6″-O-ACYLTRANSFERASE (3AT), but only MYBA1 induced F3'5'H in concordance with the low proportion of tri-hydroxylated anthocyanins found in MYBA6-A7 hairy roots. This putative new color locus is related to the red/cyanidic pigmentation of vegetative organs in black- and white-skinned cultivars, and forms part of the UV-B radiation response pathway orchestrated by ELONGATED HYPOCOTYL 5 (HY5). These results demonstrate the involvement of additional anthocyanin regulators in grapevine and suggest an evolutionary divergence between the two grape color loci for controlling additional targets of the flavonoid pathway.

CiMYB17, a stress-induced chicory R2R3-MYB transcription factor, activates promoters of genes involved in fructan synthesis and degradation

In Cichorium intybus, inulin metabolism is mediated by fructan-active enzymes (FAZYs): sucrose:sucrose 1-fructosyltransferase (1-SST), fructan:fructan 1-fructosyltransferase (1-FFT), and fructan 1-exohydrolases 1, 2a and 2b (1-FEH1, -2a and -2b), respectively. While these enzymes have been rigorously characterized, the transcriptional network orchestrating their development- and stress-related expression has remained largely unknown. Here, the possible role of R2R3-MYB transcription factors in FAZY regulation was explored via bioinformatic identification of R2R3-MYBs (using an RNA sequencing (RNAseq) database), studies of co-expression of these factors with target genes, in vivo transient transactivation assays of FAZY target promoters (dual luciferase assay), and a yeast one-hybrid assay investigating the specificity of the binding of these factors to cis-elements. The chicory MYB transcription factor CiMYB17 specifically activated promoters of 1-SST and 1-FFT by binding to the consensus DNA-motif DTTHGGT. Unexpectedly, CiMYB17 also activated promoters of fructan exohydrolase genes. The stimulatory effect on promoter activities of sucrose transporter and cell wall invertase genes points to a general role in regulating the source-sink relationship. Co-induction of CiMYB17 with 1-SST and 1-FFT (and, less consistently, with 1-FEH1/2) in nitrogen-starved or abscisic acid (ABA)-treated chicory seedlings and in salt-stressed chicory hairy roots supports a role in stress-induced fructan metabolism, including de novo fructan synthesis and trimming of pre-existing fructans, whereas the reduced expression of CiMYB17 in developing taproots excludes a role in fructan accumulation under normal growth conditions.

Genome-wide sequential, evolutionary, organizational and expression analyses of phenylpropanoid biosynthesis associated MYB domain transcription factors in Arabidopsis

The MYB gene family represents one of the largest groups of transcription factors in plants. Recent evidences have also demonstrated key role of MYB transcription factors in regulating the expression of major genes involved in the biosynthesis of phenylpropanoid compounds which confer biotic and abiotic stress tolerance in plant species. However, no comprehensive genome-wide analysis of the phenylpropanoid pathway-associated MYB transcription factors has been reported thus far. In this study, 11 Arabidopsis MYB proteins, such as MYB3, MYB4, MYB7, MYB11, MYB12, MYB32, MYB75, MYB90, MYB111, MYB113, and MYB114 were initially identified considering their reported regulatory function in phenylpropanoid biosynthesis pathway. Subsequent genome-wide analysis have identified the corresponding homologues from Glycine max, Vigna radiata, Oryza sativa, and Zea mays, while homologous of Arabidopsis MYB75, MYB90, MYB113, and MYB114 were not detected in rice and maize genomes. The identified MYB proteins were classified into three groups (I-III) based on phylogeny. Sequence and domain analysis revealed presence of two conserved DNA binding MYB domains in the selected MYB proteins. Promoter analysis indicated presence of cis-regulatory elements related to light signaling, development, and stress response. Expression analysis of selected Arabidopsis MYB genes revealed their function in plant development and abiotic stress response, consistent with gene ontology annotations. Together, these results provide a useful framework for further experimental studies for the functional characterization of the target MYB genes in the context of regulation of phenylpropanoid biosynthesis and plant stress response.

Use of Natural Diversity and Biotechnology to Increase the Quality and Nutritional Content of Tomato and Grape

Improving fruit quality has become a major goal in plant breeding. Direct approaches to tackling fruit quality traits specifically linked to consumer preferences and environmental friendliness, such as improved flavor, nutraceutical compounds, and sustainability, have slowly been added to a breeder priority list that already includes traits like productivity, efficiency, and, especially, pest and disease control. Breeders already use molecular genetic tools to improve fruit quality although most advances have been made in producer and industrial quality standards. Furthermore, progress has largely been limited to simple agronomic traits easy-to-observe, whereas the vast majority of quality attributes, specifically those relating to flavor and nutrition, are complex and have mostly been neglected. Fortunately, wild germplasm, which is used for resistance against/tolerance of environmental stresses (including pathogens), is still available and harbors significant genetic variation for taste and health-promoting traits. Similarly, heirloom/traditional varieties could be used to identify which genes contribute to flavor and health quality and, at the same time, serve as a good source of the best alleles for organoleptic quality improvement. Grape (Vitis vinifera L.) and tomato (Solanum lycopersicum L.) produce fleshy, berry-type fruits, among the most consumed in the world. Both have undergone important domestication and selection processes, that have dramatically reduced their genetic variability, and strongly standardized fruit traits. Moreover, more and more consumers are asking for sustainable production, incompatible with the wide range of chemical inputs. In the present paper, we review the genetic resources available to tomato/grape breeders, and the recent technological progresses that facilitate the identification of genes/alleles of interest within the natural or generated variability gene pool. These technologies include omics, high-throughput phenotyping/phenomics, and biotech approaches. Our review also covers a range of technologies used to transfer to tomato and grape those alleles considered of interest for fruit quality. These include traditional breeding, TILLING (Targeting Induced Local Lesions in Genomes), genetic engineering, or NPBT (New Plant Breeding Technologies). Altogether, the combined exploitation of genetic variability and innovative biotechnological tools may facilitate breeders to improve fruit quality tacking more into account the consumer standards and the needs to move forward into more sustainable farming practices.

TaPIMP2, a pathogen-induced MYB protein in wheat, contributes to host resistance to common root rot caused by Bipolaris sorokiniana

MYB transcription factors (TFs) have been implicated in various biology processes in model plants. However, functions of the great majority of MYB TFs in wheat (Triticum aestivum L.) have not been characterized. The soil-borne fungal pathogens Bipolaris sorokiniana and Rhizoctonia cerealis are the causal agents of important destructive diseases of wheat. Here, the TaPIMP2 gene, encoding a pathogen-induced MYB protein in wheat, was isolated through comparative transcriptomic analysis, and its defensive role was studied. TaPIMP2 was proved to localize in nuclei. TaPIMP2 responded in a different extent and speed upon infections of B. sorokiniana or R. cerealis. TaPIMP2 displayed different expression patterns after exogenous application of phytohormones, including abscisic acid, ethylene, and salicylic acid. Silencing of TaPIMP2 repressed resistance of wheat cultivar Yangmai 6 to B. sorokiniana, but did not alter resistance of wheat line CI12633 to R. cerealis. TaPIMP2 overexpression significantly improved resistance to B. sorokiniana rather than R. cerealis in transgenic wheat. Moreover, TaPIMP2 positively modulated the expression of pathogenesis-related genes, including PR1a, PR2, PR5, and PR10. Collectively, TaPIMP2 positively contributes to wheat resistance to B. sorokiniana possibly through regulating the expression of defense-related genes, and TaPIMP2 plays distinct roles in defense responses to different fungal infection.

The molecular mechanism underlying anthocyanin metabolism in apple using the MdMYB16 and MdbHLH33 genes

MdMYB16 forms homodimers and directly inhibits anthocyanin synthesis via its C-terminal EAR repressor. It weakened the inhibitory effect of MdMYB16 on anthocyanin synthesis when overexpressing MdbHLH33 in callus overexpressing MdMYB16. MdMYB16 could interact with MdbHLH33. Anthocyanins are strong antioxidants that play a key role in the prevention of cardiovascular disease, cancer, and diabetes. The germplasm of Malus sieversii f. neidzwetzkyana is important for the study of anthocyanin metabolism. To date, only limited studies have examined the negative regulatory mechanisms underlying anthocyanin synthesis in apple. Here, we analyzed the relationship between anthocyanin levels and MdMYB16 expression in mature Red Crisp 1-5 apple (M. domestica) fruit, generated an evolutionary tree, and identified an EAR suppression sequence and a bHLH binding motif of the MdMYB16 protein using protein sequence analyses. Overexpression of MdMYB16 or MdMYB16 without bHLH binding sequence (LBSMdMYB16) in red-fleshed callus inhibited MdUFGT and MdANS expression and anthocyanin synthesis. However, overexpression of MdMYB16 without the EAR sequence (LESMdMYB16) in red-fleshed callus had no inhibitory effect on anthocyanin. The yeast one-hybrid assay showed that MdMYB16 and LESMdMYB16 interacted the promoters of MdANS and MdUFGT, respectively. Yeast two-hybrid, pull-down, and bimolecular fluorescence complementation assays showed that MdMYB16 formed homodimers and interacted with MdbHLH33, however, the LBSMdMYB16 could not interact with MdbHLH33. We overexpressed MdbHLH33 in callus overexpressing MdMYB16 and found that it weakened the inhibitory effect of MdMYB16 on anthocyanin synthesis. Together, these results suggested that MdMYB16 and MdbHLH33 may be important part of the regulatory network controlling the anthocyanin biosynthetic pathway.

MYB12 and MYB22 play essential roles in proanthocyanidin and flavonol synthesis in red-fleshed apple (Malus sieversii f. niedzwetzkyana)

Flavonoids are major polyphenol compounds in plant secondary metabolism. Wild red-fleshed apples (Malus sieversii f. niedzwetzkyana) are an excellent resource because of their much high flavonoid content than cultivated apples. In this work, R6R6, R6R1 and R1R1 genotypes were identified in an F₁ segregating population of M. sieversii f. niedzwetzkyana. Significant differences in flavonoid composition and content were detected among the three genotypes by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry analysis. Furthermore, two putative flavonoid-related genes encoding R2R3-MYB transcription factors, designated MYB12 and MYB22, were cloned and characterized. The expression patterns of MYB12 and MYB22 directly correlated with those of leucoanthocyanidin reductase and flavonol synthase, respectively. Their roles in flavonoid biosynthesis were identified by overexpression in apple callus and ectopic expression in Arabidopsis. MYB12 expression in the Arabidopsis TT2 mutant complemented its proanthocyanidin-deficient phenotype. Likewise, MYB22 expression in an Arabidopsis triple mutant complemented its flavonol-deficient phenotype. MYB12 could interact with bHLH3 and bHLH33 and played an essential role in proanthocyanidin synthesis. MYB22 was found to activate flavonol pathways by combining directly with the flavonol synthase promoter. Our findings provide a valuable perspective on flavonoid synthesis and provide a basis for breeding elite functional apples with a high flavonoid content.

The AtMYB12 activation domain maps to a short C-terminal region of the transcription factor

The Arabidopsis thaliana R2R3-MYB transcription factor MYB12 is a light-inducible, flavonol-specific activator of flavonoid biosynthesis. The transactivation activity of the AtMYB12 protein was analyzed using a C-terminal deletion series in a transient A. thaliana protoplast assay with the goal of mapping the activation domain (AD). Although the deletion of the last 46 C-terminal amino acids did not affect the activation capacity, the deletion of the last 98 amino acids almost totally abolished transactivation of two different target promoters. A domain swap experiment using the yeast GAL4 DNA-binding domain revealed that the region from positions 282 to 328 of AtMYB12 was sufficient for transactivation. In contrast to the R2R3-MYB ADs known thus far, that of AtMYB12 is not located at the rearmost C-terminal end of the protein. The AtMYB12 AD is conserved in other experimentally proven R2R3-MYB flavonol regulators from different species.

McMYB12 Transcription Factors Co-regulate Proanthocyanidin and Anthocyanin Biosynthesis in Malus Crabapple

The flavonoid compounds, proanthocyanidins (PAs), protect plants from biotic stresses, contribute to the taste of many fruits, and are beneficial to human health in the form of dietary antioxidants. In this study, we functionally characterized two Malus crabapple R2R3-MYB transcription factors, McMYB12a and McMYB12b, which co-regulate PAs and anthocyanin biosynthesis. McMYB12a was shown to be mainly responsible for upregulating the expression of anthocyanin biosynthetic genes by binding to their promoters, but to be only partially responsible for regulating PAs biosynthetic genes. In contrast, McMYB12b showed preferential binding to the promoters of PAs biosynthetic genes. Overexpression of McMYB12a and McMYB12b in tobacco (Nicotiana tabacum) altered the expression of flavonoid biosynthetic genes and promoted the accumulation of PAs and anthocyanins in tobacco petals. Conversely, transient silencing their expression in crabapple plants, using a conserved gene region, resulted in reduced PAs and anthocyanin production a green leaf phenotype. Meanwhile, transient overexpression of the two genes and silenced McMYB12s in apple (Malus domestica) fruit had a similar effect as overexpression in tobacco and silenced in crabapple. This study reveals a new mechanism for the coordinated regulation of PAs and anthocyanin accumulation in crabapple leaves, which depends on an auto-regulatory balance involving McMYB12a and McMYB12b expression.

Isolation and molecular characterization of a Lotus japonicus R2R3-MYB subgroup 7 transcription factor gene

We isolated an ortholog (LjMYB12) of the Arabidopsis R2R3-MYB transcription factor (TF) gene from Lotus japonicus to investigate the regulation of flavonoid biosynthesis, which is driven by many paralogous genes in L. japonicus. We characterized the spatial and temporal expression of LjMYB12 in leaves, stems, roots, flowers, immature seeds, seedling leaves, and seedling roots. Expression was much higher in flowers than in other tissues. To verify the relationship between the expression of LjMYB12 and that of flavonoid biosynthesis genes, we generated transgenic L. japonicus plants overexpressing LjMYB12. Overexpression of LjMYB12 resulted in the upregulation of genes for a chalcone synthase paralog (CHS1), flavanone 3-hydroxylase, and flavonol synthase. Interestingly, LjMYB12 strongly activated CHS1 but did not activate other CHS paralogs. This result suggests differences in the spatial or temporal activation of CHS paralogs by R2R3-MYB TFs. Molecular characterization of R2R3-MYB TFs in L. japonicus will reveal the effects of gene duplication on the regulation of diverse flavonoid biosynthesis.

Sunlight Modulates Fruit Metabolic Profile and Shapes the Spatial Pattern of Compound Accumulation within the Grape Cluster

Vineyards are characterized by their large spatial variability of solar irradiance (SI) and temperature, known to effectively modulate grape metabolism. To explore the role of sunlight in shaping fruit composition and cluster uniformity, we studied the spatial pattern of incoming irradiance, fruit temperature and metabolic profile within individual grape clusters under three levels of sunlight exposure. The experiment was conducted in a vineyard of Cabernet Sauvignon cv. located in the Negev Highlands, Israel, where excess SI and midday temperatures are known to degrade grape quality. Filtering SI lowered the surface temperature of exposed fruits and increased the uniformity of irradiance and temperature in the cluster zone. SI affected the overall levels and patterns of accumulation of sugars, organic acids, amino acids and phenylpropanoids, across the grape cluster. Increased exposure to sunlight was associated with lower accumulation levels of malate, aspartate, and maleate but with higher levels of valine, leucine, and serine, in addition to the stress-related proline and GABA. Flavan-3-ols metabolites showed a negative response to SI, whereas flavonols were highly induced. The overall levels of anthocyanins decreased with increased sunlight exposure; however, a hierarchical cluster analysis revealed that the members of this family were grouped into three distinct accumulation patterns, with malvidin anthocyanins and cyanidin-glucoside showing contrasting trends. The flavonol-glucosides, quercetin and kaempferol, exhibited a logarithmic response to SI, leading to improved cluster uniformity under high-light conditions. Comparing the within-cluster variability of metabolite accumulation highlighted the stability of sugars, flavan-3-ols, and cinnamic acid metabolites to SI, in contrast to the plasticity of flavonols. A correlation-based network analysis revealed that extended exposure to SI modified metabolic coordination, increasing the number of negative correlations between metabolites in both pulp and skin. This integrated study of micrometeorology and metabolomics provided insights into the grape-cluster pattern of accumulation of 70 primary and secondary metabolites as a function of spatial variations in SI. Studying compound-specific responses against an extended gradient of quantified conditions improved our knowledge regarding the modulation of berry metabolism by SI, with the aim of using sunlight regulation to accurately modulate fruit composition in warm and arid/semi-arid regions.

Whole Plant Temperature Manipulation Affects Flavonoid Metabolism and the Transcriptome of Grapevine Berries

Among environmental factors, temperature is the one that poses serious threats to viticulture in the present and future scenarios of global climate change. In this work, we evaluated the effects on berry ripening of two thermal regimes, imposed from veraison to harvest. Potted vines were grown in two air-conditioned greenhouses with High Temperature (HT) and Low Temperature (LT) regimes characterized by 26 and 21°C as average and 42 and 35°C as maximum air daily temperature, respectively. We conducted analyses of the main berry compositional parameters, berry skin flavonoids and berry skin transcriptome on HT and LT berries sampled during ripening. The two thermal conditions strongly differentiated the berries. HT regime increased sugar accumulation at the beginning of ripening, but not at harvest, when HT treatment contributed to a slight total acidity reduction and pH increase. Conversely, growing temperatures greatly impacted on anthocyanin and flavonol concentrations, which resulted as strongly reduced, while no effects were found on skin tannins accumulation. Berry transcriptome was analyzed with several approaches in order to identify genes with different expression profile in berries ripened under HT or LT conditions. The analysis of whole transcriptome showed that the main differences emerging from this approach appeared to be more due to a shift in the ripening process, rather than to a strong rearrangement at transcriptional level, revealing that the LT temperature regime could delay berry ripening, at least in the early stages. Moreover, the results of the in-depth screening of genes differentially expressed in HT and LT did not highlight differences in the expression of transcripts involved in the biosynthesis of flavonoids (with the exception of PAL and STS) despite the enzymatic activities of PALs and UFGT being significantly higher in LT than HT. This suggests only a partial correlation between molecular and biochemical data in our conditions and the putative existence of post-transcriptional and post-translational mechanisms playing significant roles in the regulation of flavonoid metabolic pathways and in particular of anthocyanins.

Transcriptome-Wide Identification of Novel UV-B- and Light Modulated Flavonol Pathway Genes Controlled by VviMYBF1

Flavonols constitute a group of flavonoids with important photoprotective roles in plants. In addition, flavonol content and composition greatly influences fruit quality. We previously demonstrated that the grapevine R2R3-MYB transcription factor (TF) VviMYBF1 promotes flavonol accumulation by inducing the expression of flavonol synthase (VviFLS1/VviFLS4), a key step of the initial flavonol pathway. Despite this, gene networks underlying flavonol modification in grapevine including both structural and regulatory genes remain poorly understood. In order to identify flavonol modifying genes and TFs acting downstream of VviMYBF1 a microarray-based transcriptome analysis was performed on grapevine hairy roots ectopically expressing VviMYBF1 or a Green Fluorescent Protein as control. VviFLS1 was induced in VviMYBF1 transgenic roots and glycosylated flavonols accumulated significantly compared with control lines. Among the differentially expressed genes, potential flavonol-modifying enzymes with predicted rhamnosyltransferase (e.g., RhaT1) or glycosyltransferase (e.g., GT3) activities were identified. In addition, important TFs of the MYB and bZIP families such as the proanthocyanidin regulator VviMYBPA1 and the UV-B light responsive HY5 homolog VviHYH were significantly altered in their expression pattern by overexpression of VviMYBF1. Co-temporal expression analysis demonstrated positive correlation of VviMYBF1 with VviFLS1, VviGT3, and VviRhaT1 during berry development and in fruits ripened with different light and UV-B radiation conditions at field. These results show that VviMYBF1 overexpression led to the identification of novel genes of the flavonol pathway and that the flavonol modifying machinery can be influenced by agricultural practices to optimize flavonol composition in grapes.

Functional Characterization of a Novel R2R3-MYB Transcription Factor Modulating the Flavonoid Biosynthetic Pathway from Epimedium sagittatum

Epimedium species have been widely used both as traditional Chinese medicinal plants and ornamental perennials. Both flavonols, acting as the major bioactive components (BCs) and anthocyanins, predominantly contributing to the color diversity of Epimedium flowers belong to different classes of flavonoids. It is well-acknowledged that flavonoid biosynthetic pathway is predominantly regulated by R2R3-MYB transcription factor (TF) as well as bHLH TF and WD40 protein at the transcriptional level. MYB TFs specifically regulating anthocyanin or flavonol biosynthetic pathway have been already isolated and functionally characterized from Epimedium sagittatum, but a R2R3-MYB TF involved in regulating both these two pathways has not been functionally characterized to date in Epimedium plants. In this study, we report the functional characterization of EsMYB9, a R2R3-MYB TF previously isolated from E. sagittatum. The previous study indicated that EsMYB9 belongs to a small subfamily of R2R3-MYB TFs containing grape VvMYB5a and VvMYB5b TFs, which regulate flavonoid biosynthetic pathway. The present studies show that overexpression of EsMYB9 in tobacco leads to increased transcript levels of flavonoid pathway genes and increased contents of anthocyanins and flavonols. Yeast two-hybrid assay indicates that the C-terminal region of EsMYB9 contributes to the autoactivation activity, and EsMYB9 interacts with EsTT8 or AtTT8 bHLH regulator. Transient reporter assay shows that EsMYB9 slightly activates the expression of EsCHS (chalcone synthase) promoter in transiently transformed leaves of Nicotiana benthamiana, but the addition of AtTT8 or EsTT8 bHLH regulator strongly enhances the transcriptional activation of EsMYB9 against five promoters of the flavonoid pathway genes except EsFLS (flavonol synthase). In addition, co-transformation of EsMYB9 and EsTT8 in transiently transfected tobacco leaves strongly induces the expressions of flavonoid biosynthetic genes. The potential role of EsMYB9 in modulating the biosynthesis and accumulation of sucrose-induced anthocyanin and flavonol-derived BCs is also discussed. These findings suggest that EsMYB9 is a novel R2R3-MYB TF, which regulates the flavonoid biosynthetic pathway in Epimedium, but distinctly different with the anthocyanin or flavonol-specific MYB regulators identified previously in Epimedium plants.

Dissecting the Biochemical and Transcriptomic Effects of a Locally Applied Heat Treatment on Developing Cabernet Sauvignon Grape Berries

Reproductive development of grapevine and berry composition are both strongly influenced by temperature. To date, the molecular mechanisms involved in grapevine berries response to high temperatures are poorly understood. Unlike recent data that addressed the effects on berry development of elevated temperatures applied at the whole plant level, the present work particularly focuses on the fruit responses triggered by direct exposure to heat treatment (HT). In the context of climate change, this work focusing on temperature effect at the microclimate level is of particular interest as it can help to better understand the consequences of leaf removal (a common viticultural practice) on berry development. HT (+ 8°C) was locally applied to clusters from Cabernet Sauvignon fruiting cuttings at three different developmental stages (middle green, veraison and middle ripening). Samples were collected 1, 7, and 14 days after treatment and used for metabolic and transcriptomic analyses. The results showed dramatic and specific biochemical and transcriptomic changes in heat exposed berries, depending on the developmental stage and the stress duration. When applied at the herbaceous stage, HT delayed the onset of veraison. Heating also strongly altered the berry concentration of amino acids and organic acids (e.g., phenylalanine, γ-aminobutyric acid and malate) and decreased the anthocyanin content at maturity. These physiological alterations could be partly explained by the deep remodeling of transcriptome in heated berries. More than 7000 genes were deregulated in at least one of the nine experimental conditions. The most affected processes belong to the categories "stress responses," "protein metabolism" and "secondary metabolism," highlighting the intrinsic capacity of grape berries to perceive HT and to build adaptive responses. Additionally, important changes in processes related to "transport," "hormone" and "cell wall" might contribute to the postponing of veraison. Finally, opposite effects depending on heating duration were observed for genes encoding enzymes of the general phenylpropanoid pathway, suggesting that the HT-induced decrease in anthocyanin content may result from a combination of transcript abundance and product degradation.

System-Level and Granger Network Analysis of Integrated Proteomic and Metabolomic Dynamics Identifies Key Points of Grape Berry Development at the Interface of Primary and Secondary Metabolism

Grapevine is a fruit crop with worldwide economic importance. The grape berry undergoes complex biochemical changes from fruit set until ripening. This ripening process and production processes define the wine quality. Thus, a thorough understanding of berry ripening is crucial for the prediction of wine quality. For a systemic analysis of grape berry development we applied mass spectrometry based platforms to analyse the metabolome and proteome of Early Campbell at 12 stages covering major developmental phases. Primary metabolites involved in central carbon metabolism, such as sugars, organic acids and amino acids together with various bioactive secondary metabolites like flavonols, flavan-3-ols and anthocyanins were annotated and quantified. At the same time, the proteomic analysis revealed the protein dynamics of the developing grape berries. Multivariate statistical analysis of the integrated metabolomic and proteomic dataset revealed the growth trajectory and corresponding metabolites and proteins contributing most to the specific developmental process. K-means clustering analysis revealed 12 highly specific clusters of co-regulated metabolites and proteins. Granger causality network analysis allowed for the identification of time-shift correlations between metabolite-metabolite, protein- protein and protein-metabolite pairs which is especially interesting for the understanding of developmental processes. The integration of metabolite and protein dynamics with their corresponding biochemical pathways revealed an energy-linked metabolism before veraison with high abundances of amino acids and accumulation of organic acids, followed by protein and secondary metabolite synthesis. Anthocyanins were strongly accumulated after veraison whereas other flavonoids were in higher abundance at early developmental stages and decreased during the grape berry developmental processes. A comparison of the anthocyanin profile of Early Campbell to other cultivars revealed similarities to Concord grape and indicates the strong effect of genetic background on metabolic partitioning in primary and secondary metabolism.

The Transcriptional Responses and Metabolic Consequences of Acclimation to Elevated Light Exposure in Grapevine Berries

An increasing number of field studies that focus on grapevine berry development and ripening implement systems biology approaches; the results are highlighting not only the intricacies of the developmental programming/reprogramming that occurs, but also the complexity of how profoundly the microclimate influences the metabolism of the berry throughout the different stages of development. In a previous study we confirmed that a leaf removal treatment to Sauvignon Blanc grapes, grown in a highly characterized vineyard, primarily affected the level of light exposure to the berries throughout their development. A full transcriptomic analysis of berries from this model vineyard details the underlying molecular responses of the berries in reaction to the exposure and show how the berries acclimated to the imposing light stress. Gene expression involved in the protection of the photosynthetic machinery through rapid protein-turnover and the expression of photoprotective flavonoid compounds were most significantly affected in green berries. Overall, the transcriptome analysis showed that the berries implemented multiple stress-mitigation strategies in parallel and metabolite analysis was used to support the main findings. Combining the transcriptome data and amino acid profiling provided evidence that amino acid catabolism probably contributed to the mitigation of a likely energetic deficit created by the upregulation of (energetically) costly stress defense mechanisms. Furthermore, the rapid turnover of essential proteins involved in the maintenance of primary metabolism and growth in the photosynthetically active grapes appeared to provide precursors for the production of protective secondary metabolites such as apocarotenoids and flavonols in the ripening stages of the berries. Taken together, these results confirmed that the green grape berries responded to light stress much like other vegetative organs and were able to acclimate to the increased exposure, managing their metabolism and energy requirements to sustain the developmental cycle toward ripening. The typical metabolic consequences of leaf removal on grape berries can therefore now be linked to increased light exposure through mechanisms of photoprotection in green berries that leads toward acclimation responses that remain intact until ripening.

Light-induced Variation in Phenolic Compounds in Cabernet Sauvignon Grapes (Vitis vinifera L.) Involves Extensive Transcriptome Reprogramming of Biosynthetic Enzymes, Transcription Factors, and Phytohormonal Regulators

Light environments have long been known to influence grape (Vitis vinifera L.) berry development and biosynthesis of phenolic compounds, and ultimately affect wine quality. Here, the accumulation and compositional changes of hydroxycinnamic acids (HCAs) and flavonoids, as well as global gene expression were analyzed in Cabernet Sauvignon grape berries under sunlight exposure treatments at different phenological stages. Sunlight exposure did not consistently affect the accumulation of berry skin flavan-3-ol or anthocyanin among different seasons due to climatic variations, but increased HCA content significantly at véraison and harvest, and enhanced flavonol accumulation dramatically with its timing and severity degree trend. As in sunlight exposed berries, a highly significant correlation was observed between the expression of genes coding phenylalanine ammonia-lyase, 4-coumarate: CoA ligase, flavanone 3-hydroxylase and flavonol synthase family members and corresponding metabolite accumulation in the phenolic biosynthesis pathway, which may positively or negatively be regulated by MYB, bHLH, WRKY, AP2/EREBP, C2C2, NAC, and C2H2 transcription factors (TFs). Furthermore, some candidate genes required for auxin, ethylene and abscisic acid signal transductions were also identified which are probably involved in berry development and flavonoid biosynthesis in response to enhanced sunlight irradiation. Taken together, this study provides a valuable overview of the light-induced phenolic metabolism and transcriptome changes, especially the dynamic responses of TFs and signaling components of phytohormones, and contributes to the further understanding of sunlight-responsive phenolic biosynthesis regulation in grape berries.

Omics Approaches for Understanding Grapevine Berry Development: Regulatory Networks Associated with Endogenous Processes and Environmental Responses

Grapevine fruit development is a dynamic process that can be divided into three stages: formation (I), lag (II), and ripening (III), in which physiological and biochemical changes occur, leading to cell differentiation and accumulation of different solutes. These stages can be positively or negatively affected by multiple environmental factors. During the last decade, efforts have been made to understand berry development from a global perspective. Special attention has been paid to transcriptional and metabolic networks associated with the control of grape berry development, and how external factors affect the ripening process. In this review, we focus on the integration of global approaches, including proteomics, metabolomics, and especially transcriptomics, to understand grape berry development. Several aspects will be considered, including seed development and the production of seedless fruits; veraison, at which anthocyanin accumulation begins in the berry skin of colored varieties; and hormonal regulation of berry development and signaling throughout ripening, focusing on the transcriptional regulation of hormone receptors, protein kinases, and genes related to secondary messenger sensing. Finally, berry responses to different environmental factors, including abiotic (temperature, water-related stress and UV-B radiation) and biotic (fungi and viruses) stresses, and how they can significantly modify both, development and composition of vine fruit, will be discussed. Until now, advances have been made due to the application of Omics tools at different molecular levels. However, the potential of these technologies should not be limited to the study of single-level questions; instead, data obtained by these platforms should be integrated to unravel the molecular aspects of grapevine development. Therefore, the current challenge is the generation of new tools that integrate large-scale data to assess new questions in this field, and to support agronomical practices.

Dissecting the Variations of Ripening Progression and Flavonoid Metabolism in Grape Berries Grown under Double Cropping System

A double cropping system has been commercially adopted in southern China, where there is abundant sunshine and heat resources. In this viticulture system, the first growing season normally starts as a summer cropping cycle; then, the vine is pruned and forced, resulting in a second crop in winter. Due to climate differences between the summer and winter growing seasons, grape ripening progression and flavonoid metabolism vary greatly. Here, the metabolites and transcriptome of flavonoid pathways were analyzed in grapes grown under two growing seasons at different stages. Notably, the winter cropping cycle strongly increased flavonoid levels by several times in comparison to summer grapes, while the summer season took a major toll on anthocyanin and flavonol accumulation, since the winter cropping greatly triggered the expression of upstream genes in the flavonoid pathway in a coordinated expression pattern. Moreover, the ratio of VviF3'5'Hs (flavonoid 3'5'-hydroxylase) to VviF3'Hs (flavonoid 3'-hydroxylase) transcript levels correlated remarkably well with the ratio of 3'5'-substituted to 3'-substituted flavonoids, which was presumed to control the flux of intermediates into different flavonoid branches. On the other hand, the phenological phase also varied greatly in the two crops. Compared to summer cropping, winter growing season accelerated the duration from budburst to veraison, therefore advancing the onset of ripening, but also prolonging the duration of ripening progression due to the purposes to harvest high-quality grapes. The differential expression pattern of hormone-related genes between the two cropping cycles might explain this phenomenon.

The Onion (Allium cepa L.) R2R3-MYB Gene MYB1 Regulates Anthocyanin Biosynthesis

Bulb color is an important consumer trait for onion (Allium cepa L., Allioideae, Asparagales). The bulbs accumulate a range of flavonoid compounds, including anthocyanins (red), flavonols (pale yellow), and chalcones (bright yellow). Flavonoid regulation is poorly characterized in onion and in other plants belonging to the Asparagales, despite being a major plant order containing many important crop and ornamental species. R2R3-MYB transcription factors associated with the regulation of distinct branches of the flavonoid pathway were isolated from onion. These belonged to sub-groups (SGs) that commonly activate anthocyanin (SG6, MYB1) or flavonol (SG7, MYB29) production, or repress phenylpropanoid/flavonoid synthesis (SG4, MYB4, MYB5). MYB1 was demonstrated to be a positive regulator of anthocyanin biosynthesis by the induction of anthocyanin production in onion tissue when transiently overexpressed and by reduction of pigmentation when transiently repressed via RNAi. Furthermore, ectopic red pigmentation was observed in garlic (Allium sativum L.) plants stably transformed with a construct for co-overexpression of MYB1 and a bHLH partner. MYB1 also was able to complement the acyanic petal phenotype of a defined R2R3-MYB anthocyanin mutant in Antirrhinum majus of the asterid clade of eudicots. The availability of sequence information for flavonoid-related MYBs from onion enabled phylogenetic groupings to be determined across monocotyledonous and dicotyledonous species, including the identification of characteristic amino acid motifs. This analysis suggests that divergent evolution of the R2R3-MYB family has occurred between Poaceae/Orchidaceae and Allioideae species. The DNA sequences identified will be valuable for future analysis of classical flavonoid genetic loci in Allium crops and will assist the breeding of these important crop species.

De novo Transcriptome Analysis Revealed Genes Involved in Flavonoid and Vitamin C Biosynthesis in Phyllanthus emblica (L.)

Phyllanthus emblica is an affluent source of various therapeutic components. A few of them like vitamin C and flavonoids are predominant bioactive compounds that are being used in immense pharmacological applications. In-spite of numerous applications, the genomic information of this plant was limited to a few expressed sequence tags (ESTs) in DNA databases. Herein, we developed in-depth transcriptome information of P. emblica using Illumina Hiseq 2000 platform and characterized. A total of 31,285,965 high-quality reads were assembled into 91,288 contigs with the N50 value 358. Out of them, 47,267 contigs were functionally annotated using BLASTX search against NCBI-non-redundant (NR) protein database. Further, 31,366 contigs showed similarity with various gene ontology (GO) terms, and 1299 were related to different enzymes and biosynthetic pathways. We identified the transcripts related to each gene involved in flavonoid and vitamin C biosynthesis. Several cytochrome P450s (CYPs) and glucosyltransferases (GTs) genes involved in flavonoid biosynthesis and various other metabolic pathways were also documented. Further, 6510 transcription factors and 4420 EST derived simple sequence repeat (SSR) markers were also predicted. The present study enlightened various characteristic features of P. emblica genome, and provided an important resource for future molecular and functional genomics studies.

The photomorphogenic factors UV-B RECEPTOR 1, ELONGATED HYPOCOTYL 5, and HY5 HOMOLOGUE are part of the UV-B signalling pathway in grapevine and mediate flavonol accumulation in response to the environment

Grapevine (Vitis vinifera L.) is a species well known for its adaptation to radiation. However, photomorphogenic factors related to UV-B responses have not been molecularly characterized. We cloned and studied the role of UV-B RECEPTOR (UVR1), ELONGATED HYPOCOTYL 5 (HY5), and HY5 HOMOLOGUE (HYH) from V. vinifera We performed gene functional characterizations, generated co-expression networks, and tested them in different environmental conditions. These genes complemented the Arabidopsis uvr8 and hy5 mutants in morphological and secondary metabolic responses to radiation. We combined microarray and RNA sequencing (RNA-seq) data with promoter inspections to identify HY5 and HYH putative target genes and their DNA binding preferences. Despite sharing a large set of common co-expressed genes, we found different hierarchies for HY5 and HYH depending on the organ and stress condition, reflecting both co-operative and partially redundant roles. New candidate UV-B gene markers were supported by the presence of HY5-binding sites. These included a set of flavonol-related genes that were up-regulated in a HY5 transient expression assay. We irradiated in vitro plantlets and fruits from old potted vines with high and low UV-B exposures and followed the accumulation of flavonols and changes in gene expression in comparison with non-irradiated conditions. UVR1, HY5, and HYH expression varied with organ, developmental stage, and type of radiation. Surprisingly, UVR1 expression was modulated by shading and temperature in berries, but not by UV-B radiation. We propose that the UV-B response machinery favours berry flavonol accumulation through the activation of HY5 and HYH at different developmental stages at both high and low UV-B exposures.

A stilbene synthase allele from a Chinese wild grapevine confers resistance to powdery mildew by recruiting salicylic acid signalling for efficient defence

Stilbenes are central phytoalexins in Vitis, and induction of the key enzyme stilbene synthase (STS) is pivotal for disease resistance. Here, we address the potential for breeding resistance using an STS allele isolated from Chinese wild grapevine Vitis pseudoreticulata (VpSTS) by comparison with its homologue from Vitis vinifera cv. 'Carigane' (VvSTS). Although the coding regions of both alleles are very similar (>99% identity on the amino acid level), the promoter regions are significantly different. By expression in Arabidopsis as a heterologous system, we show that the allele from the wild Chinese grapevine can confer accumulation of stilbenes and resistance against the powdery mildew Golovinomyces cichoracearum, whereas the allele from the vinifera cultivar cannot. To dissect the upstream signalling driving the activation of this promoter, we used a dual-luciferase reporter system in a grapevine cell culture. We show elevated responsiveness of the promoter from the wild grape to salicylic acid (SA) and to the pathogen-associated molecular pattern (PAMP) flg22, equal induction of both alleles by jasmonic acid (JA), and a lack of response to the cell death-inducing elicitor Harpin. This elevated SA response of the VpSTS promoter depends on calcium influx, oxidative burst by RboH, mitogen-activated protein kinase (MAPK) signalling, and JA synthesis. We integrate the data in the context of a model where the resistance of V. pseudoreticulata is linked to a more efficient recruitment of SA signalling for phytoalexin synthesis.

Genome-wide Expression Analysis and Metabolite Profiling Elucidate Transcriptional Regulation of Flavonoid Biosynthesis and Modulation under Abiotic Stresses in Banana

Flavonoid biosynthesis is largely regulated at the transcriptional level due to the modulated expression of genes related to the phenylpropanoid pathway in plants. Although accumulation of different flavonoids has been reported in banana, a staple fruit crop, no detailed information is available on regulation of the biosynthesis in this important plant. We carried out genome-wide analysis of banana (Musa acuminata, AAA genome) and identified 28 genes belonging to 9 gene families associated with flavonoid biosynthesis. Expression analysis suggested spatial and temporal regulation of the identified genes in different tissues of banana. Analysis revealed enhanced expression of genes related to flavonol and proanthocyanidin (PA) biosynthesis in peel and pulp at the early developmental stages of fruit. Genes involved in anthocyanin biosynthesis were highly expressed during banana fruit ripening. In general, higher accumulation of metabolites was observed in the peel as compared to pulp tissue. A correlation between expression of genes and metabolite content was observed at the early stage of fruit development. Furthermore, this study also suggests regulation of flavonoid biosynthesis, at transcriptional level, under light and dark exposures as well as methyl jasmonate (MJ) treatment in banana.

Kaolin Foliar Application Has a Stimulatory Effect on Phenylpropanoid and Flavonoid Pathways in Grape Berries

Drought, elevated air temperature, and high evaporative demand are increasingly frequent during summer in grape growing areas like the Mediterranean basin, limiting grapevine productivity and berry quality. The foliar exogenous application of kaolin, a radiation-reflecting inert mineral, has proven effective in mitigating the negative impacts of these abiotic stresses in grapevine and other fruit crops, however, little is known about its influence on the composition of the grape berry and on key molecular mechanisms and metabolic pathways notably important for grape berry quality parameters. Here, we performed a thorough molecular and biochemical analysis to assess how foliar application of kaolin influences major secondary metabolism pathways associated with berry quality-traits, leading to biosynthesis of phenolics and anthocyanins, with a focus on the phenylpropanoid, flavonoid (both flavonol- and anthocyanin-biosynthetic) and stilbenoid pathways. In grape berries from different ripening stages, targeted transcriptional analysis by qPCR revealed that several genes involved in these pathways-VvPAL1, VvC4H1, VvSTSs, VvCHS1, VvFLS1, VvDFR, and VvUFGT-were more expressed in response to the foliar kaolin treatment, particularly in the latter maturation phases. In agreement, enzymatic activities of phenylalanine ammonia lyase (PAL), flavonol synthase (FLS), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) were about two-fold higher in mature or fully mature berries from kaolin-treated plants, suggesting regulation also at a transcriptional level. The expression of the glutathione S-transferase VvGST4, and of the tonoplast anthocyanin transporters VvMATE1 and VvABCC1 were also all significantly increased at véraison and in mature berries, thus, when anthocyanins start to accumulate in the vacuole, in agreement with previously observed higher total concentrations of phenolics and anthocyanins in berries from kaolin-treated plants, especially at full maturity stage. Metabolomic analysis by reverse phase LC-QTOF-MS confirmed several kaolin-induced modifications including a significant increase in the quantities of several secondary metabolites including flavonoids and anthocyanins in the latter ripening stages, probably resulting from the general stimulation of the phenylpropanoid and flavonoid pathways.

Characterization of a New Pink-Fruited Tomato Mutant Results in the Identification of a Null Allele of the SlMYB12 Transcription Factor

The identification and characterization of new tomato (Solanum lycopersicum) mutants affected in fruit pigmentation and nutritional content can provide valuable insights into the underlying biology, as well as a source of new alleles for breeding programs. To date, all characterized pink-pigmented tomato fruit mutants appear to result from low SlMYB12 transcript levels in the fruit skin. Two new mutant lines displaying a pink fruit phenotype (pf1 and pf2) were characterized in this study. In the pf mutants, SlMYB12 transcripts accumulated to wild-type levels but exhibited the same truncation, which resulted in the absence of the essential MYB activation domain coding region. Allelism and complementation tests revealed that both pf mutants were allelic to the y locus and showed the same recessive null allele in homozygosis: Δy A set of molecular and metabolic effects, reminiscent of those observed in the Arabidopsis (Arabidopsis thaliana) myb11 myb12 myb111 triple mutant, were found in the tomato Δy mutants. To our knowledge, these have not been described previously, and our data support the idea of their being null mutants, in contrast to previously described transcriptional hypomorphic pink fruit lines. We detected a reduction in the expression of several flavonol glycosides and some associated glycosyl transferases. Transcriptome analysis further revealed that the effects of the pf mutations extended beyond the flavonoid pathway into the interface between primary and secondary metabolism. Finally, screening for Myb-binding sites in the candidate gene promoter sequences revealed that 141 of the 152 co-down-regulated genes may be direct targets of SlMYB12 regulation.

MicroRNA858 Is a Potential Regulator of Phenylpropanoid Pathway and Plant Development

MicroRNAs (miRNAs) are endogenous, noncoding small RNAs that function as critical regulators of gene expression. In plants, miRNAs have shown their potential as regulators of growth, development, signal transduction, and stress tolerance. Although the miRNA-mediated regulation of several processes is known, the involvement of miRNAs in regulating secondary plant product biosynthesis is poorly understood. In this study, we functionally characterized Arabidopsis (Arabidopsis thaliana) miR858a, which putatively targets R2R3-MYB transcription factors involved in flavonoid biosynthesis. Overexpression of miR858a in Arabidopsis led to the down-regulation of several MYB transcription factors regulating flavonoid biosynthesis. In contrast to the robust growth and early flowering of miR858OX plants, reduction of plant growth and delayed flowering were observed in Arabidopsis transgenic lines expressing an artificial miRNA target mimic (MIM858). Genome-wide expression analysis using transgenic lines suggested that miR858a targets a number of regulatory factors that modulate the expression of downstream genes involved in plant development and hormonal and stress responses. Furthermore, higher expression of MYBs in MIM858 lines leads to redirection of the metabolic flux towards the synthesis of flavonoids at the cost of lignin synthesis. Altogether, our study has established the potential role of light-regulated miR858a in flavonoid biosynthesis and plant growth and development.

Characterization of a Citrus R2R3-MYB Transcription Factor that Regulates the Flavonol and Hydroxycinnamic Acid Biosynthesis

Flavonols and hydroxycinnamic acids are important phenylpropanoid metabolites in plants. In this study, we isolated and characterized a citrus R2R3-MYB transcription factor CsMYBF1, encoding a protein belonging to the flavonol-specific MYB subgroup. Ectopic expression of CsMYBF1 in tomato led to an up-regulation of a series of genes involved in primary metabolism and the phenylpropanoid pathway, and induced a strong accumulation of hydroxycinnamic acid compounds but not the flavonols. The RNAi suppression of CsMYBF1 in citrus callus caused a down-regulation of many phenylpropanoid pathway genes and reduced the contents of hydroxycinnamic acids and flavonols. Transactivation assays indicated that CsMYBF1 activated several promoters of phenylpropanoid pathway genes in tomato and citrus. Interestingly, CsMYBF1 could activate the CHS gene promoter in citrus, but not in tomato. Further examinations revealed that the MYBPLANT cis-elements were essential for CsMYBF1 in activating phenylpropanoid pathway genes. In summary, our data indicated that CsMYBF1 possessed the function in controlling the flavonol and hydroxycinnamic acid biosynthesis, and the regulatory differences in the target metabolite accumulation between two species may be due to the differential activation of CHS promoters by CsMYBF1. Therefore, CsMYBF1 constitutes an important gene source for the engineering of specific phenylpropanoid components.

The grapevine VvibZIPC22 transcription factor is involved in the regulation of flavonoid biosynthesis

In grapevine, flavonoids constitute one of the most abundant subgroups of secondary metabolites, influencing the quality, health value, and typicity of wines. Their synthesis in many plant species is mainly regulated at the transcriptional level by modulation of flavonoid pathway genes either by single regulators or by complexes of different regulators. In particular, bZIP and MYB factors interact synergistically in the recognition of light response units present in the promoter of some genes of the pathway, thus mediating light-dependent flavonoid biosynthesis. We recently identified VvibZIPC22, a member of clade C of the grapevine bZIP family, in a quantitative trait locus (QTL) specifically associated with kaemperol content in mature berries. Here, to validate the involvement of this candidate gene in the fine regulation of flavonol biosynthesis, we characterized its function by in vitro and in vivo experiments. A role for this gene in the control of flavonol biosynthesis was indeed confirmed by its highest expression at flowering and during UV light-mediated induction, paralleled by accumulation of the flavonol synthase 1 transcript and flavonol compounds. The overexpression of VvibZIPC22 in tobacco caused a significant increase in several flavonoids in the flower, via induction of general and specific genes of the pathway. In agreement with this evidence, VvibZIPC22 was able to activate the promoters of specific genes of the flavonoid pathway, alone or together with other factors, as revealed by transient reporter assays. These findings, supported by in silico indications, allowed us to propose VvibZIPC22 as a new regulator of flavonoid biosynthesis in grapevine.

AtMYB12 regulates flavonoids accumulation and abiotic stress tolerance in transgenic Arabidopsis thaliana

In plants, transcriptional regulation is the most important tool for modulating flavonoid biosynthesis. The AtMYB12 gene from Arabidopsis thaliana has been shown to regulate the expression of key enzyme genes involved in flavonoid biosynthesis, leading to the increased accumulation of flavonoids. In this study, the codon-optimized AtMYB12 gene was chemically synthesized. Subcellular localization analysis in onion epidermal cells indicated that AtMYB12 was localized to the nucleus. Its overexpression significantly increased accumulation of flavonoids and enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of AtMYB12 resulted in the up-regulation of genes involved in flavonoid biosynthesis, abscisic acid (ABA) biosynthesis, proline biosynthesis, stress responses and ROS scavenging under salt and drought stresses. Further analyses under salt and drought stresses showed significant increases of ABA, proline content, superoxide dismutase (SOD) and peroxidase (POD) activities, as well as significant reduction of H2O2 and malonaldehyde (MDA) content. The results demonstrate the explicit role of AtMYB12 in conferring salt and drought tolerance by increasing the levels of flavonoids and ABA in transgenic Arabidopsis. The AtMYB12 gene has the potential to be used to enhance tolerance to abiotic stresses in plants.

Two MYB transcription factors regulate flavonoid biosynthesis in pear fruit (Pyrus bretschneideri Rehd.)

Flavonoid compounds play important roles in the modern diet, and pear fruits are an excellent dietary source of these metabolites. However, information on the regulatory network of flavonoid biosynthesis in pear fruits is rare. In this work, 18 putative flavonoid-related MYB transcription factors (TFs) were screened by phylogenetic analysis and four of them were correlated with flavonoid biosynthesis patterns in pear fruits. Among these MYB-like genes, the specific functions of two novel MYB TFs, designated as PbMYB10b and PbMYB9, were further verified by both overexpression and RNAi transient assays. PbMYB10b, a PAP-type MYB TF with atypical motifs in its conserved region, regulated the anthocyanin and proanthocyanidin pathways by inducing the expression of PbDFR, but its function could be complemented by other MYB TFs. PbMYB9, a TT2-type MYB, not only acted as the specific activator of the proanthocyanidin pathway by activating the PbANR promoter, but also induced the synthesis of anthocyanins and flavonols by binding the PbUFGT1 promoter in pear fruits. The MYBCORE-like element has been identified in both the PbUFGT1 promoter and ANR promoters in most species, but it was not found in UFGT promoters isolated from other species. This finding was also supported by a yeast one-hybrid assay and thus enhanced the likelihood of the interaction between PbMYB9 and the PbUFGT1 promoter.