Arabidopsis MYB4 plays dual roles in flavonoid biosynthesis

Abstract

Flavonoids are major secondary metabolites derived from the plant phenylpropanoid pathway that play important roles in plant development and also have benefits for human health. So-called MBW ternary complexes involving R2R3-MYB and basic helix-loop-helix (bHLH) transcription factors along with WD-repeat proteins have been reported to regulate expression of the biosynthetic genes in the flavonoid pathway. MYB4 and its closest homolog MYB7 have been suggested to function as repressors of phenylpropanoid metabolism. However, the detailed mechanism by which they act has not been fully elucidated. Here, we show that Arabidopsis thaliana MYB4 and its homologs MYB7 and MYB32 interact with the bHLH transcription factors TT8, GL3 and EGL3 and thereby interfere with the transcriptional activity of the MBW complexes. In addition, MYB4 can also inhibit flavonoid accumulation by repressing expression of the gene encoding Arogenate Dehydratase 6 (ADT6), which catalyzes the final step in the biosynthesis of phenylalanine, the precursor for flavonoid biosynthesis. MYB4 potentially represses not only the conventional ADT6 encoding the plastidial enzyme but also the alternative isoform encoding the cytosolic enzyme. We suggest that MYB4 plays dual roles in modulating the flavonoid biosynthetic pathway in Arabidopsis.

MYB20, MYB42, MYB43, and MYB85 Regulate Phenylalanine and Lignin Biosynthesis during Secondary Cell Wall Formation

“…It was reported that AtMYB75 can interact with AtKNAT7, which functions as a negative regulator of secondary cell wall formation in interfascicular fibers (Bhargava et al, 2010;Wang et al, 2020a). A recent study further demonstrated that AtMYB4, a transcriptional repressor of lignin biosynthesis, along with its homologs MYB7 and MYB32, can attenuate the transcriptional function of MYB75-TT8-TTG1 complexes in flavonoid metabolism by interacting with the TT8 transcription factor (Wang et al, 2020b). The coordinated action of MYB repressors and activators has been proposed as a fine-tuning mechanism for the regulation of plant secondary metabolism (Bomal et al, 2014).…”

Gene silencing of BnaA09.ZEP and BnaC09.ZEP confers orange color in Brassica napus flowers

“…In the present study, it was expressed at significantly higher levels in APSP and CPSP than in O271, at all stages. As the negative regulator of anthocyanin and proanthocyanidin biosynthesis (Jin et al, 2000;Wang et al, 2020), MYB4 showed significantly increased expression at the Petal2 stage. One repressor of anthocyanin biosynthesis (MYBL2) and one activator of proanthocyanidin accumulation (WRKY44) were dramatically up-and down-regulated at the early flower developmental stages, respectively (Ishida et al, 2007;Dubos et al, 2008), corresponding to the unaltered expression level of most of the late pathway genes in anthocyanin and proanthocyanidin biosynthesis.…”

Identification of Regulatory SNPs Associated with Vicine and Convicine Content of Vicia faba Based on Genotyping by Sequencing Data Using Deep Learning

“…MYB4 in particular regulates abiotic stress responses towards UV-B light and cadmium toxicity in Arabidopsis thaliana [82,83] and cold in Oryza sativa [84]. It has also been shown to influence the biosynthesis of flavonoids [85]. MYB61 participates in the response to cold stress in Medicago truncatula [86].…”