The Arabidopsis Transcription Factor MYB12 Is a Flavonol-Specific Regulator of Phenylpropanoid Biosynthesis

Abstract

Comprehensive functional data on plant R2R3-MYB transcription factors is still scarce compared to the manifold of their occurrence. Here, we identified the Arabidopsis (Arabidopsis thaliana) R2R3-MYB transcription factor MYB12 as a flavonolspecific activator of flavonoid biosynthesis. Transient expression in Arabidopsis protoplasts revealed a high degree of functional similarity between MYB12 and the structurally closely related factor P from maize (Zea mays). Both displayed similar target gene specificity, and both activated target gene promoters only in the presence of a functional MYB recognition element. The genes encoding the flavonoid biosynthesis enzymes chalcone synthase, chalcone flavanone isomerase, flavanone 3-hydroxylase, and flavonol synthase were identified as target genes. Hence, our observations further add to the general notion of a close relationship between structure and function of R2R3-MYB factors. High-performance liquid chromatography analyses of myb12 mutant plants and MYB12 overexpression plants demonstrate a tight linkage between the expression level of functional MYB12 and the flavonol content of young seedlings. Quantitative real time reverse transcription-PCR using these mutant plants showed MYB12 to be a transcriptional regulator of CHALCONE SYNTHASE and FLAVONOL SYNTHASE in planta, the gene products of which are indispensable for the biosynthesis of flavonols.

Retracted: Nitric oxide enhances plant ultraviolet‐B protection up‐regulating gene expression of the phenylpropanoid biosynthetic pathway

“…Among the R2R3 MYB, it has been demonstrated that the maize P gene (ZmP) and its Arabidopsis functional homolog MYB12 control the transcriptional activation of the phenylpropanoid biosynthetic genes chalcone synthase (CHS), chalcone isomerase (CHI), flavonone 3-hydroxylase (F3H) and flavonol synthase 1 (FLS1) (Grotewold 2005;Mehrtens et al 2005;Luo et al 2008). Furthermore, it was reported that ZmP as well as MYB12 are up-regulated by UV-B exposure (Casati & Walbot 2005;Oravecz et al 2006).…”

Transcription Factors of Lotus: Regulation of Isoflavonoid Biosynthesis Requires Coordinated Changes in Transcription Factor Activity

“…The induction of isoflavonoid biosynthesis by elicitation was accompanied by significant decreases in transcript levels of genes encoding members of other R2R3MYB subgroups, including subgroups 4, 7, and 13, which are known to regulate branches of phenylpropanoid metabolism (Jin et al, 2000;Newman et al, 2004;Mehrtens et al, 2005). Members of subgroup 4 are repressors of targeting genes of the GPP (Jin et al, 2000) or monolignol biosynthesis (Legay et al, 2007).…”

“…Down-regulation of members of subgroups 7 and 13 reflects their roles in positively regulating competing pathway branches. The primary role of genes belonging to subgroup 7 is the control of the genes encoding the enzymes in the flavonoid pathway, including CHS and CHI, required for flavonol biosynthesis in dicot plants and 3-deoxy-flavonoid biosynthesis in monocot plants (Grotewold et al, 1994;Mehrtens et al, 2005). The fact that two genes from this subgroup showed a large decrease in steady-state transcript levels upon elicitation in our experiments and that this was mirrored by down-regulation of CHS1, FLAVANONE 3-HYDROXYLASE (F3H), and FLS suggested that the flavonol branch of the flavonoid pathway competes for the precursors required for isoflavonoid biosynthesis and that the reduced expression of the subgroup 7 TFs likely plays a role in directing the flux of metabolites into the isoflavonoid pathway.…”

“…This plant-specific TF family is defined by a common DNA-binding domain of two repeats of about 50 amino acids. Examination of R2R3MYB TFs by phylogenetic analysis has revealed functionally distinct subgroups (Stracke et al, 2001;Jiang et al, 2004;Dubos et al, 2010), of which several are involved in the regulation of particular branches of phenylpropanoid metabolism; for example, anthocyanin production (PazAres et al, 1987;Quattrocchio et al, 1998;Schwinn et al, 2006), phlobaphene biosynthesis (Grotewold et al, 1994), flavonol biosynthesis (Mehrtens et al, 2005), hydroxycinnamic acid biosynthesis (Tamagnone et al, 1998;Jin et al, 2000), and monolignol biosynthesis (Zhou et al, 2009;Zhong et al, 2010). In legumes, there is an extra dimension to the regulatory control of phenylpropanoid metabolism because they produce isoflavonoids that serve as phytoalexins and as signaling molecules for nodulation (Subramanian et al, 2007).…”

MYB-related transcription factors function as regulators of the circadian clock and anthocyanin biosynthesis in Arabidopsis

“…For example, MYB11, MYB12, MYB111, MYB75/ PAP1, and AtMYBD work as positive regulators whereas MYB-LIKE 2 (MYBL2) functions as a negative regulator. 17,19,[27][28][29][30] Among them, MYB75/PAP1 is a master regulator of the anthocyanin biosynthesis pathway; 19,31 however, direct evidence reflecting whether or not PAP1 can act on the circadian regulation of this biosynthesis pathway is still lacking. 32 Currently, a study has revealed that 2 circadian components NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED (LNK) and RVE8 collaborate to control the anthocyanin metabolic pathway.…”