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

Yongyan Peng,Dwayne J Jensen,Amali H Thrimawithana,Andrew C Allan,Richard V Espley,Janine M Cooney

doi:10.1038/s41598-020-70977-0

Yongyan Peng, Dwayne J Jensen + Show 4 more

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https://doi.org/10.1038/s41598-020-70977-0

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Journal: Scientific Reports	Publication Date: Aug 25, 2020
Citations: 48	License type: open-access

Affiliation: University of Auckland, Plant & Food Research

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.

Highlights

The groups of plant flavonoid metabolites termed anthocyanins and proanthocyanins (PA) are responsible for pigmentation in seeds, flowers and fruits
Anthocyanin is produced by the biosynthetic pathway consisting of the commonly termed early biosynthetic enzymes, chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 3′-hydroxylase (F3′H), flavonoid 3′,5′-hydroxylase (F3′5′H) and the late biosynthetic enzymes dihydroflavonol 4-reductase (DFR), leucoanthocyanidin dioxygenase (LDOX), and flavonoid-3-glucosyltransferase (F3GT)[2]
Dihydroflavonols produced by F3′H and F3′5′H can be converted to flavonols by flavonol synthase (FLS) or leucoanthocyanins by DFR, which can be converted to the anthocyanidin aglycone by Leucoanthocyanidin dioxygenase (LDOX) or flavanols by leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR)

Summary

Introduction

The groups of plant flavonoid metabolites termed anthocyanins and proanthocyanins (PA) are responsible for pigmentation in seeds, flowers and fruits. 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. These results suggest that while previously characterised anthocyanin activator MYBs regulate the overall anthocyanin biosynthesis pathway, the PA-related TFs, MYBC1 and WRKY44, regulate key branch points This adds a layer of regulatory control that potentially balances anthocyanin and PA levels. The MYB TFs from subgroup 6 have been implicated in the general activation of the anthocyanin pathway, such as Arabidopsis AtPAP1, apple MdMYB10, Petunia PH4, strawberry FaMYB10, grape VvMYBA1, kiwifruit MYB10/MYB110 and potato StMYBA1 and A N110–19. CsMYB5a and CsMYB5e demonstrated the ability to regulate the accumulation of both anthocyanin and PA by activating the associated genes[34]

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