Myb14, a direct activator of STS, is associated with resveratrol content variation in berry skin in two grape cultivars

Combined analysis of Polygonum cuspidatum transcriptome and metabolome revealed that PcMYB62, a transcription factor, responds to methyl jasmonate and inhibits resveratrol biosynthesis

A comparative transcriptomic and metabolomic analysis of Polygonum cuspidatum leaves treated with MeJA was carried out to investigate the regulatory mechanisms of its active compounds. A total of 692 metabolites and 77,198 unigenes were obtained, including 200 differentially accumulated metabolites and 6819 differentially expressed genes. We screened potential regulatory transcription factors involved in resveratrol and flavonoids biosynthesis, and successfully identified an MYB transcription factor, PcMYB62, which could significantly decrease the resveratrol content in P. cuspidatum leaves when over-expressed. PcMYB62 could directly bind to the MBS motifs in the promoter region of stilbene synthase (PcSTS) gene and repress its expression. Besides, PcMYB62 could also repress PcSTS expression and resveratrol biosynthesis in transgenic Arabidopsis thaliana. Our results provide abundant candidate genes for further investigation, and the new finding of the inhibitory role of PcMYB62 on the resveratrol biosynthesis could also potentially be used in metabolic engineering of resveratrol in P. cuspidatum.

Vitis Myb14 confer cold and drought tolerance by activating lipid transfer protein genes expression and reactive oxygen species scavenge

The R2R3 Myb transcription factor exhibits a wide range of functions and participates in various biological processes in plant development, secondary metabolism, and abiotic stress tolerance, among others. Vitis Myb14 initially identified for its involvement in resveratrol synthesis in grapevines. In this study, we investigate its role in abiotic stress tolerance. Significant differences in expression were observed between two grape varieties, Vitis amurensis (Cold-hardy) and V. vinifera (Cold-sentitive), under abiotic and hormone treatments. Both VvMyb14 and VaMyb14 demonstrated responsiveness to cold, drought and high salt treatment, but VaMyb14 exhibited a quicker and more pronounced response. To investigate further, we overexpressed VaMyb14 in A. thalina and found that VaMyb14 OE plants showed significantly enhanced cold and drought tolerance compared to wild-type plants. Additionally, the transgenic lines exhibited increased antioxidant enzyme activity, particularly POD activity, and reduced MDA content. Microarray analysis of VaMyb14 OE plants revealed up-regulation of several ABA metabolism and signal transduction genes, including several LTPs, PP2Cs, RD29B, COR78 and other structural genes, indicating that VaMyb14 has the capacity to reprogram a significant signaling pathway. Furthermore, comparative mRNA sequencing profiling of 35S:VaMyb14 grapevine callus indicated its involvement its function involved in ROS scavenging and ABA signaling. These findings collectively demonstrate that Vitis Myb14 serves as a critical regulator in grapevine stress responses, contributing to improved defense against necrotrophic pathogens, enhanced phytoalexin resveratrol production, and increased drought or cold tolerance.

The R2R3-MYB transcription factor CsMYB42 regulates theanine biosynthesis in albino tea leaves

Theanine is a unique secondary metabolite in tea plants and contributes to the umami taste and health benefits of tea. However, theanine biosynthesis in tea plants is not fully understood, and its mechanism of transcriptional regulation remains poorly reported. Theanine content was significantly correlated with the expression of theanine biosynthesis-related gene CsGS1c and transcription factor CsMYB42 in different leaf positions and picking times, but there was no significant correlation in different tissues of albino tea plant 'Anjibaicha'. This suggests that CsMYB42 may regulate CsGS1c to synthesize theanine in albino tea leaves, and the regulation is tissue specific. CsMYB42 is a nuclear-localized R2R3-MYB transcription factor gene with transcriptional activation activity. Yeast one-hybrid assay and electrophoretic mobility shift assay confirmed the direct binding of CsMYB42 to the promoter of CsGS1c. Luciferase assay showed that CsMYB42 activates the CsGS1c expression. Furthermore, the inhibition of CsMYB42 using an antisense oligonucleotide in tea leaves decreased CsGS1c expression and theanine content. These results indicate that CsMYB42 plays a crucial role in activating the expression of CsGS1c and may be involved in the biosynthesis of theanine in albino tea leaves. This study provides fresh insights into the tissue-specific regulation of theanine biosynthesis, which laid a foundation for breeding high-theanine tea plants.

VqMAPK3/VqMAPK6, VqWRKY33, and VqNSTS3 constitute a regulatory node in enhancing resistance to powdery mildew in grapevine

Grapevine powdery mildew is caused by Erysiphe necator, which seriously harms grape production in the world. Stilbene synthase makes phytoalexins that contribute to the resistance of grapevine against powdery mildew. A novel VqNSTS3 was identified and cloned from Chinese wild Vitis quinquangularis accession Danfeng-2. The novel VqNSTS3 was transferred into susceptible 'Thompson Seedless' by Agrobacterium-mediated transformation. The transgenic plants showed resistance to the disease and activated other resistance-related genes. VqNSTS3 expression in grapevine is regulated by VqWRKY33, and which binds to TTGACC in the VqNSTS3 promoter. Furthermore, VqWRKY33 was phosphorylated by VqMAPK3/VqMAPK6 and thus led to enhanced signal transduction and increased VqNSTS3 expression. ProVqNSTS3::VqNSTS3-GFP of transgenic VqNSTS3 in Arabidopsis thaliana was observed to move to and wrap the pathogen's haustoria and block invasion by Golovinomyces cichoracearum. These results demonstrate that stilbene accumulation of novel VqNSTS3 of the Chinese wild Vitis quinquangularis accession Danfeng-2 prevented pathogen invasion and enhanced resistance to powdery mildew. Therefore, VqNSTS3 can be used in generating powdery mildew-resistant grapevines.

Advances in understanding cold tolerance in grapevine

Grapevine (Vitis ssp.) is a deciduous perennial fruit crop, and the canes and buds of grapevine should withstand low temperatures annually during winter. However, the widely cultivated Vitis vinifera is cold-sensitive and cannot survive the severe winter in regions with extremely low temperatures, such as viticulture regions in northern China. By contrast, a few wild Vitis species like V. amurensis and V. riparia exhibit excellent freezing tolerance. However, the mechanisms underlying grapevine cold tolerance remain largely unknown. In recent years, much progress has been made in elucidating the mechanisms, owing to the advances in sequencing and molecular biotechnology. Assembly of grapevine genomes together with resequencing and transcriptome data enable researchers to conduct genomic and transcriptomic analyses in various grapevine genotypes and populations to explore genetic variations involved in cold tolerance. In addition, a number of pivotal genes have been identified and functionally characterized. In this review, we summarize recent major advances in physiological and molecular analyses of cold tolerance in grapevine and put forward questions in this field. We also discuss the strategies for improving the tolerance of grapevine to cold stress. Understanding grapevine cold tolerance will facilitate the development of grapevines for adaption to global climate change.

Genome-wide characterization and functional identification of MYB genes in Malus sieversii infected by Valsa mali

Among the most important transcription factors in plants, the v-myb avian myeloblastosis viral oncogene homolog (MYB) regulates the expression network of response genes under stresses such as fungal infection. In China, the canker disease Valsa mali threatens the survival of Malus sieversii, an ancestor of cultivated apples. Using the M. sieversii genome, we identified 457 MsMYB and 128 R2R3-MsMYB genes that were randomly distributed across 17 chromosomes. Based on protein sequence and structure, the R2R3-MsMYB genes were phylogenetically divided into 29 categories, and 26 conserved motifs were identified. We further predicted cis-elements in the 2000-kb promoter region of R2R3-MsMYBs based on the genome. Transcriptome analysis of M. sieversii under V. mali infection showed that 27 R2R3-MsMYBs were significantly differentially expressed, indicating their key role in the response to V. mali infection. Using transient transformation, MsMYB14, MsMYB24, MsMYB39, MsMYB78, and MsMYB108, which were strongly induced by V. mali infection, were functionally identified. Among the five MsMYBs, MsMYB14 and MsMYB78 were both important in enhancing resistance to diseases, whereas MsMYB24 inhibited resistance. Based on the results of this study, we gained a better understanding of the MsMYB transcription factor family and laid the foundation for a future research program on disease prevention strategies in M. sieversii.

Effect of VaMyb40 and VaMyb60 Overexpression on Stilbene Biosynthesis in Cell Cultures of Grapevine Vitis amurensis Rupr

Stilbenes are plant defense compounds known to rapidly accumulate in grapevine and some other plant species in response to microbial infection and several abiotic stresses. Stilbenes have attracted considerable attention due to valuable biological effects with multi-spectrum therapeutic application. However, there is a lack of information on natural signaling pathways and transcription factors regulating stilbene biosynthesis. It has been previously shown that MYB R2R3 transcription factor genes VaMyb40 and VaMyb60 were up-regulated in cell cultures of wild-growing grapevine Vitis amurensis Rupr. in response to UV irradiation. In this study, the effects of VaMyb40 or VaMyb60 overexpression in cell cultures of V. amurensis on their capability to produce stilbenes were investigated. Overexpression of the VaMyb60 gene led to a considerable increase in the content of stilbenes in three independently transformed transgenic lines in 5.9–13.9 times, while overexpression of the VaMyb40 gene also increased the content of stilbenes, although to a lesser extent (in 3.4–4.0 times) in comparison with stilbene levels in the empty vector-transformed calli. Stilbene content and stilbene production in the VaMyb60-transgenic calli reached 18.8 mg/g of dry weight (DW) and 150.8 mg/L, respectively. Using HPLC analysis, we detected eight individual stilbenes: t-resveratrol diglucoside, t-piceid, t-resveratrol, ε-viniferin, δ-viniferin, cis-resveratrol, cis-piceid, t-piceatannol. T-resveratrol prevailed over other stilbenoid compounds (53.1–89.5% of all stilbenes) in the VaMyb-overexpressing cell cultures. Moreover, the VaMyb40- and VaMyb60-transformed calli were capable of producing anthocyanins up to 0.035 mg/g DW, while the control calli did not produce anthocyanins. These findings show that the VaMyb40 and VaMyb60 genes positively regulate the stilbene biosynthesis as strong positive transcription regulators and can be used in biotechnological applications for stilbene production or high-quality viticulture and winemaking.

Effect of Calmodulin-like Gene (CML) Overexpression on Stilbene Biosynthesis in Cell Cultures of Vitis amurensis Rupr

Stilbenes are plant phenolics known to rapidly accumulate in grapevine and other plants in response to injury or pathogen attack and to exhibit a great variety of healing beneficial effects. It has previously been shown that several calmodulin-like protein (CML) genes were highly up-regulated in cell cultures of wild-growing grapevine Vitis amurensis Rupr. in response to stilbene-modulating conditions, such as stress hormones, UV-C, and stilbene precursors. Both CML functions and stilbene biosynthesis regulation are still poorly understood. In this study, we investigated the effect of overexpression of five VaCML genes on stilbene and biomass accumulation in the transformed cell cultures of V. amurensis. We obtained 16 transgenic cell lines transformed with the VaCML52, VaCML65, VaCML86, VaCML93, and VaCML95 genes (3–4 independent lines per gene) under the control of the double CaMV 35S promoter. HPLC-MS analysis showed that overexpression of the VaCML65 led to a considerable and consistent increase in the content of stilbenes of 3.8–23.7 times in all transformed lines in comparison with the control calli, while biomass accumulation was not affected. Transformation of the V. amurensis cells with other analyzed VaCML genes did not lead to a consistent and considerable effect on stilbene biosynthesis in the cell lines. The results indicate that the VaCML65 gene is implicated in the signaling pathway regulating stilbene biosynthesis as a strong positive regulator and can be useful in viticulture and winemaking for obtaining grape cultivars with a high content of stilbenes and stress resistance.

VqMYB154 promotes polygene expression and enhances resistance to pathogens in Chinese wild grapevine

Resveratrol plays a crucial phytoalexin role in the grapevine and is beneficial to human health. However, the molecular mechanism of resveratrol accumulation in the enhancement of disease resistance is unclear. Here, we report that the transcription factor VqMYB154 from Vitis quinquangularis accession Danfeng-2 is strongly expressed under artificial inoculation with Uncinula necator and regulates resveratrol accumulation. Unlike its homolog, VqMYB154 has a pathogen-induced promoter and responds to stimulation by U. necator, Pseudomonas syringae, and other treatments. Yeast one-hybrid and GUS activity assays confirmed that VqMYB154 can activate the stilbene synthase genes VqSTS9, VqSTS32, and VqSTS42 by directly binding to their promoters. Overexpression of VqMYB154 in grape leaves resulted in activation of the stilbene pathway, upregulation of STS genes, and accumulation of stilbenoids. In addition, heterologous overexpression of VqMYB154 in Arabidopsis activated resistance-related genes and resulted in greater programmed cell death and accumulation of reactive oxygen species, which led to resistance against P. syringae. These results suggest that the transcription factor VqMYB154 from V. quinquangularis accession Danfeng-2 participates in the regulatory mechanism that improves the biosynthesis and accumulation of stilbenes and enhances resistance to disease in grapevine.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

Coexpression analysis of a large-scale transcriptome identified a calmodulin-like protein regulating the development of adventitious roots in poplar

Poplars are important woody plants, and the ability to form adventitious roots (ARs) is the key factor for their cultivation because most poplars are propagated by cloning. In previous studies, Ca2+ was confirmed to regulate AR formation in poplar. In this study, wild-type poplar cuttings grown in 1.0 mM Ca2+ solution showed the best visible performance of AR development. Coexpression analysis of a large-scale RNA-Seq transcriptome was conducted to identify Ca2+-related genes that regulate AR development in poplar. A total of 15 coexpression modules (CMs) were identified, and two CMs showed high association with AR development. Functional analysis identified a number of biological pathways, including 'oxidation-reduction process', 'response to biotic stimulus' and 'metabolic process', in tissues of AR development. The Ca2+-related pathway was specifically selected, and its regulation in poplar AR development was predicted. A Ca2+ sensor, PdeCML23-1, which is a member of the calmodulin-like protein (CML) family, was found to promote AR development by phenotypic assay of overexpressed PdeCML23-1 transgenic lines at various growing conditions. By measuring cytosolic Ca2+ in AR tips, PdeCML23-1 seemed to play a role in decreasing cytosolic Ca2+ concentration. Additionally, the expression profiles of some genes and phytohormone indole acetic acid (IAA) were also changed in the overexpressed PdeCML23-1 transgenic lines. According to this study, we were able to provide a global view of gene regulation for poplar AR development. Moreover, we also observed the regulation of cytosolic Ca2+ concentration by PdeCML23-1, and this regulation was involved in AR development in poplar. We also predicted that PdeCML23-1 possibly regulates AR development by modulating IAA content in poplar.

The WRKY53 transcription factor enhances stilbene synthesis and disease resistance by interacting with MYB14 and MYB15 in Chinese wild grape

Resveratrol is notable not only for its functions in disease resistance in plants but also for its health benefits when it forms part of the human diet. Identification of new transcription factors helps to reveal the regulatory mechanisms of stilbene synthesis. Here, the WRKY53 transcription factor was isolated from the Chinese wild grape, Vitis quinquangularis. Vqwrky53 was expressed in a variety of tissues and responded to powdery mildew infection and to exogenous hormone application. VqWRKY53 was located in the nucleus and had transcriptional activation activity in yeast. A yeast two-hybrid assay and a bimolecular fluorescence complementation assay confirmed that VqWRKY53 interacted physically with VqMYB14 and VqMYB15, which have previously been reported to regulate stilbene synthesis. When Vqwrky53 was overexpressed in grape leaves, the expression of VqSTS32 and VqSTS41 and the content of stilbenes were increased. A yeast one-hybrid assay demonstrated that VqWRKY53 could bind directly to the promoters of STS genes. Overexpression of Vqwrky53 activated β-glucuronidase expression, driven by STS promoters, and co-expressing Vqwrky53 with VqMYB14 and VqMYB15 showed stronger regulatory functions. Heterologous overexpression of Vqwrky53 in Arabidopsis accelerated leaf senescence and disease resistance to PstDC3000.

Role of Resveratrol in Regulating Cutaneous Functions

Protective role of the skin is against external insults and maintenance of electrolyte homeostasis of the body. Cutaneous dysfunction can account for the development of both cutaneous and systemic disorders. Thus, improvements in cutaneous functions can benefit a number of extracutaneous and cutaneous functions. Resveratrol, a natural ingredient, displays multiple benefits for various systems/organs, including the skin. The benefits of resveratrol for cutaneous functions include stimulation of keratinocyte differentiation and antimicrobial peptide expression, inhibition of keratinocyte proliferation and cutaneous inflammation, UV protection, anticancer, antiaging, and inhibition of melanogenesis. The mechanisms of action of resveratrol include activation of sirtuin 1 and nuclear factor erythroid 2-related factor 2, and inhibition of mitogen-activated protein kinase signaling. Evidence suggests that topical resveratrol could be a valuable alternative not only for daily skin care, but also for the prevention and treatment of various cutaneous disorders. This review summarizes the benefits of resveratrol for cutaneous functions.

Molecular Analysis of UV-C Induced Resveratrol Accumulation in Polygonum cuspidatum Leaves

Resveratrol is one of the most studied plant secondary metabolites owing to its numerous health benefits. It is accumulated in some plants following biotic and abiotic stress pressures, including UV-C irradiation. Polygonum cuspidatum represents the major natural source of concentrated resveratrol but the underlying mechanisms as well as the effects of UV-C irradiation on resveratrol content have not yet been documented. Herein, we found that UV-C irradiation significantly increased by 2.6-fold and 1.6-fold the resveratrol content in irradiated leaf samples followed by a dark incubation for 6 h and 12 h, respectively, compared to the untreated samples. De novo transcriptome sequencing and assembly resulted into 165,013 unigenes with 98 unigenes mapped to the resveratrol biosynthetic pathway. Differential expression analysis showed that P.cuspidatum strongly induced the genes directly involved in the resveratrol synthesis, including phenylalanine ammonia-lyase, cinnamic acid 4-hydroxylase, 4-coumarate-CoA ligase and stilbene synthase (STS) genes, while strongly decreased the chalcone synthase (CHS) genes after exposure to UV-C. Since CHS and STS share the same substrate, P. cuspidatum tends to preferentially divert the substrate to the resveratrol synthesis pathway under UV-C treatment. We identified several members of the MYB, bHLH and ERF families as potential regulators of the resveratrol biosynthesis genes.

VqbZIP1 isolated from Chinese wild Vitis quinquangularis is involved in the ABA signaling pathway and regulates stilbene synthesis

Resveratrol is an important phytoalexin in grapevine. Not only does it confer increased disease resistance and but as a food component it offers significant benefits in human health. Abscisic acid (ABA) is an important phytohormone involved in many biological processes in plants and can also promote the accumulation of stilbenes. Stilbene synthase (STS) is an important enzyme which catalyzes the last step of resveratrol synthesis. Our study characterizes a basic leucine zipper (bZIP) transcription factor, VqbZIP1, isolated from Chinese wild Vitis quinquangularis accession Danfeng-2. The results show that VqbZIP1 encodes 299 amino acids and belongs to the Group A subfamily of the bZIP family. VqbZIP1 showed transcriptional activation activity in yeast and is predicted to be located in the nucleus. The yeast two-hybrid assay and bimolecular fluorescence complementation (BiFC) assay together show that VqbZIP1 interacts with VqSnRK2.4 and VqSnRK2.6. VqbZIP1, the STS genes, VqSnRK2.4 and VqSnRK2.6 can all be induced by ABA treatment. A GUS activity experiment indicates VqbZIP1 can activate the GUS reporter gene driven by STS promoters. Further studies show that co-expression of VqbZIP1 with VqSnRK2.4 or VqSnRK2.6 can confer higher efficiency than expression of VqbZIP1 alone in activating the STS promoters. Overexpression of VqbZIP1 in grape leaves promoted the transcript level of the STS genes and the accumulation of stilbenes. Overexpression of VqbZIP1 in Arabidopsis thaliana can confer ABA sensitivity. In summary, our results suggest VqbZIP1 participates in the ABA signaling pathway and regulates stilbene synthesis.

Transcription factor VqERF114 regulates stilbene synthesis in Chinese wild Vitis quinquangularis by interacting with VqMYB35

VqERF114 regulates stilbene synthesis by interacting with VqMYB35. Resveratrol is a stilbene, an important class of secondary metabolites that accumulates in some plant species, including grapevine. In the plant, these are involved in the response to attack by plant pathogens and, as a component of the human diet, they offer a range of significant health benefits. Stilbene synthase (STS), the key enzyme responsible for resveratrol synthesis, has been characterised in a small number of plant species. However, the regulatory mechanisms for stilbene synthesis are uncertain. Here, an ERF family transcription factor from Chinese wild Vitis quinquangularis, VqERF114, was characterised as an indirect regulator of stilbene synthesis. A transient overexpression assay of VqERF114 in grapevine leaves led to increased STS expression and stilbene accumulation. However, VqERF114 did not bind to the promoters of VqSTSs but the MYB transcription factor, VqMYB35, did interact with VqERF114. This interaction was confirmed by a yeast two-hybrid assay and bimolecular fluorescence complementation. Furthermore, VqMYB35 showed activation effects on the expressions of VqSTS15, VqSTS28, VqSTS42 and VqSTS46 by binding directly to the MBS elements in their promoters. Co-overexpression of VqERF114 and VqMYB35 resulted in higher VqSTSs expression and more stilbene synthesis. These results demonstrate that VqERF114 regulates stilbene synthesis by interacting with VqMYB35.

Transcriptional regulation of stilbene synthases in grapevine germplasm differentially susceptible to downy mildew

BACKGROUND

To limit the impact of the downy mildew disease of grapevine and reduce the need to recur to chemical treatments, an effective strategy might be recovering adaptive resistance traits in both cultivated and wild V. vinifera germplasm. Considering that stilbenes represent the most important class of phytoalexins in the Vitaceae, the constitutive expression and transcriptional activation of all the functional members of the stilbene synthase gene family were analysed in a group of nine grapevine genotypes following artificial infection with the oomycete Plasmopara viticola, the causal agent of the disease. In addition, in the same genotypes we analyzed the expression of genes encoding for two transcription factors involved in the transcriptional regulation of the stilbene synthase genes, namely VvMYB14 and VvMYB15, and of genes encoding for chalcone synthases.

RESULTS

Downy mildew incidence and severity ranged from nihil to high in the grapevine genotypes considered, being low to moderate in a subgroup of V. vinifera genotypes. The constitutive expression of the stilbene synthase genes as well as the extent of their transcriptional activation following P. viticola inoculation appeared to be inversely related to the proneness to develop disease symptoms upon infection. In a specular manner, following P. viticola inoculation all the chalcone synthase genes were up-regulated in the susceptible grapevine genotypes and down-regulated in the resistant ones. The infection brought by P. viticola appeared to elicit a co-ordinated and sequential transcriptional activation of distinct stilbene synthase genes subsets, each of which may be regulated by a distinct and specific MYB transcription factor.

CONCLUSIONS

The present results suggest that the induction of stilbene biosynthesis may contribute to the basal immunity against the downy mildew of grapevine, thus representing an adaptive resistance trait to recover, in both cultivated and wild V. vinifera germplasm. During the early stages of P. viticola infection, an antagonistic interaction between flavonol and stilbene biosynthesis might occur, whose outcome might determine the subsequent extent of disease symptoms. Further studies are needed to decipher the possible regulatory mechanisms involved in the antagonistic crosstalk between these two metabolic pathways in resistant and susceptible genotypes in response to P. viticola.

Grapevine comparative early transcriptomic profiling suggests that Flavescence dorée phytoplasma represses plant responses induced by vector feeding in susceptible varieties

Background

Flavescence dorée is the most serious grapevine yellows disease in Europe. It is caused by phytoplasmas which are transmitted from grapevine to grapevine by the leafhopper Scaphoideus titanus. Differences in susceptibility among grapevine varieties suggest the existence of specific genetic features associated with resistance to the phytoplasma and/or possibly with its vector. In this work, RNA-Seq was used to compare early transcriptional changes occurring during the three-trophic interaction between the phytoplasma, its vector and the grapevine, represented by two different cultivars, one very susceptible to the disease and the other scarcely susceptible.

Results

The comparative analysis of the constitutive transcriptomic profiles suggests the existence of passive defense strategies against the insect and/or the phytoplasma in the scarcely-susceptible cultivar. Moreover, the attack by the infective vector on the scarcely-susceptible variety prompted immediate and substantial transcriptomic changes that led to the rapid erection of further active defenses. On the other hand, in the most susceptible variety the response was delayed and mainly consisted of the induction of phytoalexin synthesis. Surprisingly, the jasmonic acid- and ethylene-mediated defense reactions, activated by the susceptible cultivar following FD-free insect feeding, were not detected in the presence of the phytoplasma-infected vector.

Conclusions

The comparison of the transcriptomic response in two grapevine varieties with different levels of susceptibility to Flavescence dorèe highlighted both passive and active defense mechanisms against the vector and/or the pathogen in the scarcely-susceptible variety, as well as the capacity of the phytoplasmas to repress the defense reaction against the insect in the susceptible variety.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5908-6) contains supplementary material, which is available to authorized users.

VvWRKY8 represses stilbene synthase genes through direct interaction with VvMYB14 to control resveratrol biosynthesis in grapevine

Resveratrol (Res) is a stilbenoid, a group of plant phenolic metabolites derived from stilbene that possess activities against pests, pathogens, and abiotic stresses. Only a few species, including grapevine (Vitis), synthesize and accumulate Res. Although stilbene synthases (STSs) have been isolated and characterized in several species, the gene regulatory mechanisms underlying stilbene biosynthesis are still largely unknown. Here, we characterize a grapevine WRKY transcription factor, VvWRKY8, that regulates the Res biosynthetic pathway. Transient and stable overexpression of VvWRKY8 in grapevine results in decreased expression of VvSTS15/21 and VvMYB14, as well as in a reduction of Res accumulation. VvWRKY8 does not bind to or activate the promoters of VvMYB14 and VvSTS15/21; however, it physically interacts with VvMYB14 proteins through their N-terminal domains to prevent them from binding to the VvSTS15/21 promoter. Application of exogenous Res results in the stimulation of VvWRKY8 expression and in a decrease of VvMYB14 and VvSTS15/21 expression in grapevine suspension cells, and in the activation of the VvWRKY8 promoter in tobacco leaves. These results demonstrate that VvWRKY8 represses VvSTS15/21 expression and Res biosynthesis through interaction with VvMYB14. In this context, the VvMYB14-VvSTS15/21-Res-VvWRKY8 regulatory loop may be an important mechanism for the fine-tuning of Res biosynthesis in grapevine.

MYBs Drive Novel Consumer Traits in Fruits and Vegetables

Eating plant-derived compounds can lead to a longer and healthier life and also benefits the environment. Innovation in the fresh food sector, as well as new cultivars, can improve consumption of fruit and vegetables, with MYB transcription factors being a target to drive this novelty. Plant MYB transcription factors are implicated in diverse roles including development, hormone signalling, and metabolite biosynthesis. The reds and blues of fruit and vegetables provided by anthocyanins, phlobaphenes, and betalains are controlled by specific R2R3 MYBs. New studies are now revealing that MYBs also control carotenoid biosynthesis and other quality traits, such as flavour and texture. Future breeding techniques may manipulate or create alleles of key MYB transcription factors.

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.

Regulation of stilbene biosynthesis in plants

This review analyzes the advances in understanding the natural signaling pathways and environmental factors regulating stilbene biosynthesis. We also discuss the studies reporting on stilbene content and repertoire in plants. Stilbenes, including the most-studied stilbene resveratrol, are a family of phenolic plant secondary metabolites that have been the subject of intensive research due to their valuable pharmaceutical effects and contribution to plant disease resistance. Understanding the natural mechanisms regulating stilbene biosynthesis in plants could be useful for both the development of new plant protection strategies and for commercial stilbene production. In this review, we focus on the environmental factors and cell signaling pathways regulating stilbene biosynthesis in plants and make a comparison with the regulation of flavonoid biosynthesis. This review also analyzes the recent data on stilbene biosynthetic genes and summarizes the available studies reporting on both stilbene content and stilbene composition in different plant families.

Factor Analysis of MYB Gene Expression and Flavonoid Affecting Petal Color in Three Crabapple Cultivars

Flavonoid biosynthesis has received much attention concerning the structural genes and expression of the associated transcription factors (TFs). In the present study, we examined the gene expression patterns for petals of three colors using a statistical method. Factor analysis was successfully used to examine the expression patterns most present during regulation. The first expression patterns in the white and red petals were clearly demonstrated and have revealed different mechanisms of producing the proper components, whereas that in the pink petals was more complex, requiring factor analysis to supplement the other results. Combining the results of the correlation analysis between TFs and structural genes, the effects of each TF on the main expression pattern in each cultivar were determined. Moreover, McMYB10 was implicated in the regulation of the gene expression pattern in red petals, and McMYB5 was implicated in the maintenance of the balance of the pigment components and proanthocyanin (PA) production in cooperation with McMYB4 to generate pigmentation in the pink petals.

Insights into the Mechanisms Underlying Ultraviolet-C Induced Resveratrol Metabolism in Grapevine (V. amurensis Rupr.) cv. "Tonghua-3"

Stilbene compounds belong to a family of secondary metabolites that are derived from the phenylpropanoid pathway. Production of the stilbene phytoalexin, resveratrol, in grape (Vitis spp.) berries is known to be induced by ultraviolet-C radiation (UV-C), which has numerous regulatory effects on plant physiology. While previous studies have described changes in gene expression caused by UV-C light in several plant species, such information has yet to be reported for grapevine. We investigated both the resveratrol content and gene expression responses of berries from V. amurensis cv. Tonghua-3 following UV-C treatment, to accelerate research into resveratrol metabolism. Comparative RNA-Seq profiling of UV-C treated and untreated grape berries resulted in the identification of a large number of differentially expressed genes. Gene ontology (GO) term classification and biochemical pathway analyses suggested that UV-C treatment caused changes in various cellular processes, as well as in both hormone and secondary metabolism. The data further indicate that UV-C induced increases in resveratrol may be related to the transcriptional regulation of genes involved in the production of secondary metabolites and signaling, as well as several transcription factors. We also observed that following UV-C treatment, 22 stilbene synthase (STS) genes exhibited increases in their expression levels and a VaSTS promoter drove the expression of the GUS reporter gene when expressed in tobacco. We therefore propose that UV-C induction of VaSTS expression is an important factor in promoting resveratrol accumulation. This transcriptome data set provides new insight into the response of grape berries to UV-C treatment, and suggests candidate genes, or promoter activity of related genes, that could be used in future functional and molecular biological studies of resveratrol metabolism.

Short day transcriptomic programming during induction of dormancy in grapevine

Bud dormancy in grapevine is an adaptive strategy for the survival of drought, high and low temperatures and freeze dehydration stress that limit the range of cultivar adaptation. Therefore, development of a comprehensive understanding of the biological mechanisms involved in bud dormancy is needed to promote advances in selection and breeding, and to develop improved cultural practices for existing grape cultivars. The seasonally indeterminate grapevine, which continuously develops compound axillary buds during the growing season, provides an excellent system for dissecting dormancy, because the grapevine does not transition through terminal bud development prior to dormancy. This study used gene expression patterns and targeted metabolite analysis of two grapevine genotypes that are short photoperiod responsive (Vitis riparia) and non-responsive (V. hybrid, Seyval) for dormancy development to determine differences between bud maturation and dormancy commitment. Grapevine gene expression and metabolites were monitored at seven time points under long (LD, 15 h) and short (SD, 13 h) day treatments. The use of age-matched buds and a small (2 h) photoperiod difference minimized developmental differences and allowed us to separate general photoperiod from dormancy specific gene responses. Gene expression profiles indicated three distinct phases (perception, induction and dormancy) in SD-induced dormancy development in V. riparia. Different genes from the NAC DOMAIN CONTAINING PROTEIN 19 and WRKY families of transcription factors were differentially expressed in each phase of dormancy. Metabolite and transcriptome analyses indicated ABA, trehalose, raffinose and resveratrol compounds have a potential role in dormancy commitment. Finally, a comparison between V. riparia compound axillary bud dormancy and dormancy responses in other species emphasized the relationship between dormancy and the expression of RESVERATROL SYNTHASE and genes associated with C3HC4-TYPE RING FINGER and NAC DOMAIN CONTAINING PROTEIN 19 transcription factors.

Changing trends in biotechnology of secondary metabolism in medicinal and aromatic plants

Medicinal and aromatic plants are known to produce secondary metabolites that find uses as flavoring agents, fragrances, insecticides, dyes and drugs. Biotechnology offers several choices through which secondary metabolism in medicinal plants can be altered in innovative ways, to overproduce phytochemicals of interest, to reduce the content of toxic compounds or even to produce novel chemicals. Detailed investigation of chromatin organization and microRNAs affecting biosynthesis of secondary metabolites as well as exploring cryptic biosynthetic clusters and synthetic biology options, may provide additional ways to harness this resource. Plant secondary metabolites are a fascinating class of phytochemicals exhibiting immense chemical diversity. Considerable enigma regarding their natural biological functions and the vast array of pharmacological activities, amongst other uses, make secondary metabolites interesting and important candidates for research. Here, we present an update on changing trends in the biotechnological approaches that are used to understand and exploit the secondary metabolism in medicinal and aromatic plants. Bioprocessing in the form of suspension culture, organ culture or transformed hairy roots has been successful in scaling up secondary metabolite production in many cases. Pathway elucidation and metabolic engineering have been useful to get enhanced yield of the metabolite of interest; or, for producing novel metabolites. Heterologous expression of putative plant secondary metabolite biosynthesis genes in a microbe is useful to validate their functions, and in some cases, also, to produce plant metabolites in microbes. Endophytes, the microbes that normally colonize plant tissues, may also produce the phytochemicals produced by the host plant. The review also provides perspectives on future research in the field.