The proanthocyanin-related transcription factors MYBC1 and WRKY44 regulate branch points in the kiwifruit anthocyanin pathway

Sci Rep. 2020 Aug 25;10(1):14161. doi: 10.1038/s41598-020-70977-0.

Abstract

The groups of plant flavonoid metabolites termed anthocyanins and proanthocyanins (PA) are responsible for pigmentation in seeds, flowers and fruits. Anthocyanins and PAs are produced by a pathway of enzymes which are transcriptionally regulated by transcription factors (TFs) that form the MYB-bHLH-WD40 (MBW) complex. In this study, transcriptomic analysis of purple-pigmented kiwifruit skin and flesh tissues identified MYBC1, from subgroup 5 of the R2R3 MYB family, and WRKY44 (highly similar to Arabidopsis TTG2) as candidate activators of the anthocyanin pathway. Transient over-expression of MYBC1 and WRKY44 induced anthocyanin accumulation in tobacco leaves. Dual luciferase promoter activation assays revealed that both MYBC1 and WRKY44 were able to strongly activate the promoters of the kiwifruit F3'H and F3'5'H genes. These enzymes are branch points of the pathway which specifies the type of anthocyanin accumulated. Stable over-expression of MYBC1 and WRKY44 in kiwifruit calli activated the expression of F3'5'H and PA-related biosynthetic genes as well as increasing levels of PAs. These results suggest that while previously characterised anthocyanin activator MYBs regulate the overall anthocyanin biosynthesis pathway, the PA-related TFs, MYBC1 and WRKY44, more specifically regulate key branch points. This adds a layer of regulatory control that potentially balances anthocyanin and PA levels.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actinidia / classification
  • Actinidia / genetics
  • Actinidia / metabolism*
  • Amino Acid Motifs
  • Anthocyanins / biosynthesis*
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism
  • Flavonoids / biosynthesis
  • Fruit / metabolism
  • Gene Expression Regulation, Plant*
  • Nicotiana / metabolism
  • Phylogeny
  • Pigments, Biological / biosynthesis
  • Plant Leaves / metabolism
  • Plant Proteins / biosynthesis
  • Plant Proteins / genetics
  • Plant Proteins / physiology*
  • Plants, Genetically Modified
  • Promoter Regions, Genetic / genetics
  • Recombinant Proteins / metabolism
  • Species Specificity
  • Transcription Factors / physiology*
  • Transcriptome

Substances

  • Anthocyanins
  • Basic Helix-Loop-Helix Transcription Factors
  • Flavonoids
  • Pigments, Biological
  • Plant Proteins
  • Recombinant Proteins
  • Transcription Factors
  • Cytochrome P-450 Enzyme System
  • flavonoid 3',5'-hydroxylase
  • flavonoid 3'-hydroxylase