Arabidopsis MYB4 plays dual roles in flavonoid biosynthesis

• Published in: The Plant journal : for cell and molecular biology Vol. 101; no. 3; pp. 637 - 652
• Main Authors: Wang, Xiao‐Chen, Wu, Jie, Guan, Meng‐Ling, Zhao, Cui‐Huan, Geng, Pan, Zhao, Qiao
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.02.2020
• Subjects: anthocyanins; Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - physiology; Biosynthesis; Biosynthetic Pathways; Dehydration; Enzymes; Flavonoids; Flavonoids - metabolism; Gene expression; Helix-loop-helix proteins (basic); Homology; mediator; Metabolism; Metabolites; Phenylalanine; Prephenate Dehydrogenase - genetics; Prephenate Dehydrogenase - metabolism; proanthocyanidins; Repressor Proteins - genetics; Repressor Proteins - metabolism; Repressors; Secondary metabolites; Transcription factors; proanthocyanidins; anthocyanins; phenylalanine; mediator
• DOI: 10.1111/tpj.14570
• ISSN: 0960-7412

SUMMARY 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. Significance Statement Our results indicate that MYB4 can attenuate the transcriptional function of MYB‐bHLH‐WDR complexes, which are major regulators of flavonoid metabolism, by interacting with bHLH proteins. MYB4 directly represses the transcription of ADT6 encoding the enzyme catalyzing the last step of phenylalanine biosynthesis. These observations reveal unexpected cross‐talk between primary and secondary metabolism.