VvMYB14 participates in melatonin-induced proanthocyanidin biosynthesis by upregulating expression of VvMYBPA1 and VvMYBPA2 in grape seeds

Ethylene increases the NaHCO3 stress tolerance of grapevines partially via the VvERF1B-VvMYC2-VvPMA10 pathway

Here, we evaluated the role of ethylene in regulating the NaHCO3 stress tolerance of grapevines and clarified the mechanism by which VvERF1B regulates the response to NaHCO3 stress. The exogenous application of ACC and VvACS3 overexpression in grapevines and grape calli revealed that ethylene increased NaHCO3 stress tolerance, and this was accompanied by increased plasma membrane H+-ATPase (PMA) activity. The expression of VvERF1B was strongly induced by ACC, and overexpression of this gene in grapevines conferred increased NaHCO3 stress tolerance and enhanced PMA activity and H+ and oxalate secretion. Additionally, the function of VvERF1B was also verified using mutant transgenic grape calli and overexpression in Arabidopsis plants. The expression of VvPMA10 was strongly induced following the overexpression of VvERF1B in grapevine roots, and VvPMA10 was shown to regulate PMA activity, oxalate and H+ secretion, and NaHCO3 stress tolerance via its overexpression and mutation in grapevine roots, calli, and/or Arabidopsis. However, VvPMA10 was not a direct target gene of VvERF1B but was directly transactivated by VvMYC2. The function of VvMYC2 was shown to be similar to that of VvPMA10 via its overexpression and mutation in grape calli. Additional experiments revealed that the interaction of VvERF1B with VvMYC2 increased its ability to activate VvPMA10 expression and that VvMYC2 played a role in the VvERF1B-mediated pathway. Overall, the VvERF1B-VvMYC2-VvPMA pathway played a role in regulating ethylene-induced NaHCO3 stress tolerance in grapevines, and this process contributed to increases in PMA activity and H+ and oxalate secretion.

An activator-represssor complex of VvWRKYs regulate proanthocyanidins biosynthesis through co-targeting VvLAR in grape

Proanthocyanidins (PAs) are vital polyphenolic compounds in plants with various biological functions. Although WRKY transcription factors are known to play important roles, their specific involvement in regulating PAs metabolism in grapes remains underexplored. In this study, we identified six candidate WRKY genes potentially involved in PAs synthesis by transiently overexpressing them in Nicotiana tabacum leaves. Among these, VvWRKY57 was found to enhance PAs synthesis. Further functional analysis, achieved by overexpressing of VvWRKY57 in grape calli, confirmed its positive role in PAs biosynthesis. Using yeast one-hybrid (Y1H), dual-luciferase reporter (DLR) assays, and electrophoretic mobility shift assay (EMSA), we demonstrated that VvWRKY57 binds to the promoter of leucocyanidin reductase (VvLAR2) and stimulates its activity. Additionally, yeast two-hybrid (Y2H), bimolecular fluorescence complementary (BiFC), and pull-down assays revealed that VvWRKY57 forms heterodimers with VvWRKY20, while VvWTKY20 also forms homodimers. Interestingly, overexpression of VvWRKY20 was found to inhibit PAs synthesis. Y1H, DLR, and EMSA further showed that VvWRKY20 binds to the promoters of VvLAR1 and VvLAR2, repressing their transcription activity. When VvWRKY57 and VvWRKY20 were co-expressed, VvLAR2 promoter activity and PAs synthesis were suppressed. Moreover, we discovered that VvPUB26, an E3 ubiquitin ligase physically interacts with both VvWRKY57 and VvWRKY20. VvPUB26 mediated the degradation of VvWRKY20 but did not influence the degradation of VvWRKY57. In conclusion, this study highlights the regulatory interplay between WRKY transcription factors in PAs biosynthesis, offering insights into their distinct roles in modulating this important metabolic pathway in grapes.

AcMYB96 promotes anthocyanin accumulation in onion (Allium cepa L) without forming the MBW complex

Anthocyanins are major flavonoid compounds with established health benefits. Although the molecular mechanisms of MYB transcription factors (TFs) within the MYB-basic helix-loop-helix (bHLH)-WD-repeat protein (MBW) complex in anthocyanin biosynthesis have been revealed, the functions of other MYB TFs that are unable to form the MBW complex in this process remain unclear. In this study, we uncovered and extensively characterized an R2R3-MYB TF in onion (Allium cepa L.), named AcMYB96, which was identified as a potential anthocyanin activator. AcMYB96 was classified into subgroup 1 of the R2R3-MYB TF family and lacked the conserved sequences required for interactions with bHLH IIIf TFs. Consistently, yeast two-hybrid assays showed that AcMYB96 did not interact with any bHLH IIIf TFs examined, including AcB2 and AtTT8. The transcription pattern of AcMYB96 correlated with the level of anthocyanin accumulation, and its role in activating anthocyanin biosynthesis was confirmed through overexpression in the epithelial cells of onion bulbs and Arabidopsis. Yeast one-hybrid, electrophoretic mobility shift, and promoter transactivation assays further demonstrated that AcMYB96 promoted anthocyanin biosynthesis by binding to the promoters of the chalcone synthase (AcCHS1), anthocyanidin synthase (AcANS), and UDP-glucose-flavonoid 3-O-glucosyltransferase (AcUFGT) genes, thereby activating their expression independent of bHLH IIIf TFs. These results demonstrate that AcMYB96 activates anthocyanin biosynthesis without forming the MBW complex, providing a theoretical foundation to further enrich the gene resources for promoting anthocyanin accumulation and breeding red onions with high anthocyanin content.

Ubiquitin ligase VvPUB26 in grapevine promotes proanthocyanidin synthesis and resistance to powdery mildew

Proanthocyanidins (PAs) are an important group of flavonoids that contribute to astringency, color, and flavor in grapes (Vitis vinifera) and wines. They also play a crucial role in enhancing plant resistance to various stresses. However, the underlying regulatory mechanism governing PAs biosynthesis, particularly in relation to conferring resistance to powdery mildew, has not been extensively explored. This study focused on identifying a key player in PAs biosynthesis, namely the plant U-box (PUB) E3 ubiquitin ligase VvPUB26. We discovered that overexpression of VvPUB26 in grapes leads to a significant increase in PAs content, whereas interfering with VvPUB26 has the opposite effect. Additionally, our findings demonstrated that overexpression of VvPUB26 in transgenic grapevines enhances defense against powdery mildew while interfering with VvPUB26 results in increased susceptibility to the pathogen. Interestingly, we observed that VvPUB26 interacts with the WRKY transcription factor VvWRKY24, thereby facilitating ubiquitination and degradation processes. Through RNA-Seq analysis, we found that VvWRKY24 primarily participates in secondary metabolites biosynthesis, metabolic pathways, and plant-pathogen interaction. Notably, VvWRKY24 directly interacts with the promoters of dihydroflavonol-4-reductase (DFR) and leucoanthocyanidin reductase (LAR) to inhibit PAs biosynthesis. Meanwhile, VvWRKY24 also influences the expression of MYB transcription factor genes related to PAs synthesis. In conclusion, our results unveil a regulatory module involving VvPUB26-VvWRKY24-VvDFR/VvLAR that plays a fundamental role in governing PAs biosynthesis in grapevines. These findings enhance our understanding of the relationship between PAs biosynthesis and defense mechanisms against powdery mildew.

Regulatory Mechanism of Proanthocyanidins in Grape Peels Using vvi-miR828a and Its Target Gene VvMYBPA1

Anthocyanins and proanthocyanidins are considered to be essential secondary metabolites in grapes and are used to regulate metabolic processes, while miRNAs are involved in their synthesis of anthocyanins and proanthocyanidins to regulate metabolic processes. The present research work was carried out to investigate the underlying regulatory mechanism of target genes in the grape cultivars 'Italia' and 'Benitaka'. miRNA and transnscriptomic sequencing technology were employed to characterize both the profiles of miRNAs and the transcripts of grape peels at 10 and 11 weeks post flowering (10 wpf and 11 wpf). The results revealed that the expression level of vvi-miR828a in 'Italia' at 10 and 11 wpf was significantly higher than that in 'Benitaka'. miRNA-seq analysis predicted MYBPA1 to be the target gene of vvi-miR828a. In transcriptome analysis, the expression level of the VvMYBPA1 gene in 'Benitaka' was significantly higher than that in 'Italia'; in addition, the TPM values (expression levels) of VvMYBPA1 and miR828a also showed an evident negative correlation. The determination of the proanthocyanidin (PA) content in 'Italia' and 'Benitaka' peels at 11 wpf demonstrated that the PA content of 'Benitaka' was significantly higher than that of 'Italia'. The outcomes of RT-qRCR analysis exhibited that the expression levels of the VdPAL, VdCHS, VdCHI, VdDFR, VdMYB5b, VdANR, and VdMYBPA1 genes related anthocyanin and proanthocyanidin pathways were reduced, while the expression levels of all of the above genes were increased after the transient expression of the VvMYBPA1 vector into grape leaves. The results of the transient overexpression experiment of vvi-miR828a before the veraison period of strawberry fruits showed that vvi-miR828a can significantly slow down the coloration of strawberries. The vvi-miR828a negatively regulates the accumulation of proanthocyanidins in grape fruits by inhibiting the expression of VvMYBPA1.

Overexpression of a 'Beta' MYB Factor Gene, VhMYB15, Increases Salinity and Drought Tolerance in Arabidopsis thaliana

'Beta' is a hybrid of Vitis riparia L. and V. labrusca and has a strong ability to adapt to adverse growth environments and is mainly cultivated and used as a resistant rootstock. At present, the most extensively studied MYB TFs are R2R3-type, which have been found to be involved in plant growth, development, and stress response processes. In the present research, VhMYB15, a key transcription factor for abiotic stress tolerance, was screened by bioinformatics in 'Beta' rootstock, and its function under salinity and drought stresses was investigated. VhMYB15 was highly expressed in roots and mature leave under salinity and drought stresses. Observing the phenotype and calculating the survival rate of plants, it was found that VhMYB15-overexpressing plants exhibited relatively less yellowing and wilting of leaves and a higher survival rate under salinity and drought stresses. Consistent with the above results, through the determination of stress-related physiological indicators and the expression analysis of stress-related genes (AtSOS2, AtSOS3, AtSOS1, AtNHX1, AtSnRK2.6, AtNCED3, AtP5CS1, and AtCAT1), it was found that transgenic Arabidopsis showed better stress tolerance and stronger adaptability under salinity and drought stresses. Based on the above data, it was preliminarily indicated that VhMYB15 may be a key factor in salinity and drought regulation networks, enhancing the adaptability of 'Beta' to adverse environments.

The Influence of Melatonin Treatment in the Vinification of Feteasca Neagra and Cabernet Sauvignon Wines on the Profile of Polyphenolic Compounds and Antioxidant Activity

Until recently, the main antioxidant role among wine constituents was attributed to polyphenolic compounds, but once the presence of melatonin in wines was confirmed, an interesting new field of research opened up due to its possible synergistic effects with other antioxidants in the winemaking process, which may lead to a change in the profile of polyphenolic compounds and antioxidant activity. In order to investigate the evolution of active principles from the phenylpropanoid metabolism associated with the synergistic effects of melatonin, for the first time, a melatonin treatment was performed in the pre-stage of the different winemaking processes of Feteasca Neagra and Cabernet Sauvignon wines with different melatonin concentrations. After comparing the acquired results for the evolution of the polyphenolic compound profile and antioxidant activity of treated wines, we ascertained an increase in the antioxidant compound concentrations, especially in resveratrol, quercetin, and cyanidin-3-glucoside, directly proportional to the used melatonin concentration; an intensification in activity of PAL and C4H enzymes; and the modification in the expression of specific anthocyanin biosynthesis genes, especially UDP-D-glucose-flavonoid-3-O-glycosyltransferase. It was also shown that the application of melatonin in the pre-stage of the winemaking process can be successfully used to obtain red wines with increased antioxidant activity (almost 14%).