R2R3 MYB transcription factors: key regulators of the flavonoid biosynthetic pathway in grapevine

Abstract

Flavonoids compose one of the most abundant and important subgroups of secondary metabolites with more than 6,000 compounds detected so far in higher plants. They are found in various compositions and concentrations in nearly all plant tissues. Besides the attraction of pollinators and dispersers to fruits and flowers, flavonoids also protect against a plethora of stresses including pathogen attack, wounding and UV irradiation. Flavonoid content and composition of fruits such as grapes, bilberries, strawberries and apples as well as food extracts such as green tea, wine and chocolate have been associated with fruit quality including taste, colour and health-promoting effects. To unravel the beneficial potentials of flavonoids on fruit quality, research has been focused recently on the molecular basis of flavonoid biosynthesis and regulation in economically important fruit-producing plants such as grapevine (Vitis vinifera L.). Transcription factors and genes encoding biosynthetic enzymes have been characterized, studies that set a benchmark for future research on the regulatory networks controlling flavonoid biosynthesis and diversity. This review summarizes recent advances in the knowledge of regulatory cascades involved in flavonoid biosynthesis in grapevine. Transcriptional regulation of flavonoid biosynthesis during berry development is highlighted, with a particular focus on MYB transcription factors as molecular clocks, key regulators and powerful biotechnological tools to identify novel pathway enzymes to optimize flavonoid content and composition in grapes.

The R2R3-MYB Transcription Factors MYB14 and MYB15 Regulate Stilbene Biosynthesis in Vitis vinifera

“…To date, transcription factors (TFs) regulating the expression of structural genes for stilbene synthesis have not yet been identified. However, recently, a growing number of TFs have been demonstrated to be responsible for the regulation of PP biosynthesis in a range of plant species, including grapevine, which represents one of the most studied crop plants in terms of the regulation of the flavonoid biosynthetic pathway (Figure 1; reviewed in Czemmel et al, 2012). For example, the grapevine MYB TFs MYB5a and MYB5b were found to modulate several branches of the flavonoid pathway, regulating structural genes, such as LEUCOANTHOCYANIDIN REDUCTASE (LAR), ANTHO-CYANIDIN REDUCTASE (ANR), FLAVONOID 39-HYDROXYLASE, and CHALCONE ISOMERASE (Deluc et al, 2006(Deluc et al, , 2008.…”

Skin Browning and Expression of PPO, STS, and CHS Genes in the Grape Berries of ‘Shine Muscat’

“…5). A W-Box motif, a binding domain of the WRKY protein known as a stress responsive element (Ülker and Somssich, 2004), binding motifs of Myc and Myb genes, which are transcription factors involved in the flavonoid biosynthesis pathway (Czemmel et al, 2012), and phytohormone responsive motifs, including abscisic acid (ABA)-related, ethylene-related, and gibberellin acid (GA)-related motifs, were plotted on the promoter sequences (Table 3; Fig. 5).…”

“…In a comparison of VvPPO1 and VvPPO2 promoter sequences, without considering the motif directions, VvPPO1 contains more ABA-and ethylene-related motifs, whereas VvPPO2 contains more Myb binding and W-box motifs. ABA is generally considered an important phytohormone in grape berry maturation (Coombe and Hale, 1973) and recently, Myb transcription factor genes were also considered to be key regulators of polyphenol biosynthesis in grapevine (Czemmel et al, 2012;Höll et al, 2013). The specific increase in VvPPO2 gene expression during skin browning may be regulated and mediated by Myb transcription factors and W-box motifs responding to several stresses at the berry maturation stage.…”

“…In the context of biosynthesis progression, polyphenol oxidase, laccase, and peroxidase play important roles in metabolic pathways such as lignin biosynthesis and phenol compound polymerization (Pezet et al, 2003;Tavares et al, 2013;Zamboni et al, 2010). Recently, molecular bases for the regulation of these biosynthetic pathways have been researched intensively in grapevine (Czemmel et al, 2012;Tillett et al, 2011;Vannozzi et al, 2012). In the berry skin of 'Shine Muscat', similar induction and activation of those biosynthetic pathways could have been replaced by skin browning because increases in the expression levels of VvSTS type B and VvCHS1 were observed along with browning.…”

Identification of a Novel DFR-A Mutant Allele Determining the Bulb Color Difference between Red and Yellow Onions (Allium cepa L.)

“…In addition, regulatory genes controlling transcription of structural genes in the pathway have also been isolated in some model species such as Arabidopsis, petunia, and maize. The ternary complex consisting of R2R3-MYB, bHLH, and WD40 transcription factors is commonly identified as major regulatory genes (Ramsay and Glover 2005;Petroni and Tonelli 2011;Czemmel et al 2012).…”