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The MYB transcription factor PbMYB12b positively regulates flavonol biosynthesis in pear fruit.

ABSTRACT: BACKGROUND:As a class of natural antioxidants in plants, fruit flavonol metabolites are beneficial to human health. However, the regulatory networks for flavonol biosynthesis in most fruits are largely unknown. Previously, we reported a spontaneous pear bud sport 'Red Zaosu' (Pyrus bretschneideri Rehd.) with a high flavonoid content in its fruit. The identification of the flavonol biosynthetic regulatory network in this mutant pear fruit is crucial for elucidating the flavonol biosynthetic mechanism in fruit. RESULTS:Here, we demonstrated the PbMYB12b positively regulated flavonols biosynthesis in 'Red Zaosu' fruit. Initially, we investigated the accumulation patterns of four major quercetin glycosides and two major isorhamnetin glycosides in the fruit of 'Red Zaosu' and its wild-type 'Zaosu'. A PRODUCTION OF FLAVONOL GLYCOSIDES (PFG)-type MYB transcription factor PbMYB12b was also screened for because of its correlation with flavonol accumulation in pear fruit. The biofunction of PbMYB12b was verified by transient overexpression and RNAi assays in pear fruit and young leaves. Overexpression of PbMYB12b enhanced the biosynthesis of quercetin glycosides and isorhamnetin glycosides by positively regulating a general flavonoids biosynthesis gene PbCHSb and a flavonol biosynthesis gene PbFLS. This finding was also supported by dual-luciferase transient expression assay and transient ?-glucuronidase (GUS) reporter assay. CONCLUSIONS:Our study indicated that PbMYB12b positively regulated flavonol biosynthesis, including four major quercetin glycosides and two major isorhamnetin glycosides, by promoting the expression of PbCHSb and PbFLS in pear fruit.

SUBMITTER: Zhai R

PROVIDER: S-EPMC6385385 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Project description:Flavonols as plant secondary metabolites with vital roles in plant development and defense against UV light, have been demonstrated to be the main bioactive components (BCs) in the genus Epimedium plants, several species of which are used as materials for Herba Epimedii, an important traditional Chinese medicine. The flavonol biosynthetic pathway genes had been already isolated from Epimedium sagittatum, but a R2R3-MYB transcription factor regulating the flavonol synthesis has not been functionally characterized so far in Epimedium plants. In this study, we isolated and characterized the R2R3-MYB transcription factor EsMYBF1 involved in regulation of the flavonol biosynthetic pathway from E. sagittatum. Sequence analysis indicated that EsMYBF1 belongs to the subgroup 7 of R2R3-MYB family which contains the flavonol-specific MYB regulators identified to date. Transient reporter assay showed that EsMYBF1 strongly activated the promoters of EsF3H (flavanone 3-hydroxylase) and EsFLS (flavonol synthase), but not the promoters of EsDFRs (dihydroflavonol 4-reductase) and EsANS (anthocyanidin synthase) in transiently transformed Nicotiana benthamiana leaves. Both yeast two-hybrid assay and transient reporter assay validated EsMYBF1 to be independent of EsTT8, or AtTT8 bHLH regulators of the flavonoid pathway as cofactors. Ectopic expression of EsMYBF1 in transgenic tobacco resulted in the increased flavonol content and the decreased anthocyanin content in flowers. Correspondingly, the structural genes involved in flavonol synthesis were upregulated in the EsMYBF1 overexpression lines, including NtCHS (chalcone synthase), NtCHI (chalcone isomerase), NtF3H and NtFLS, whereas the late biosynthetic genes of the anthocyanin pathway (NtDFR and NtANS) were remarkably downregulated, compared to the controls. These results suggest that EsMYBF1 is a flavonol-specific R2R3-MYB regulator, and involved in regulation of the biosynthesis of the flavonol-derived BCs in E. sagittatum. Thus, identification and functional characterization of EsMYBF1 provide insight into understanding the biosynthesis and regulation of the flavonol-derived BCs in Epimedium plants, and also provide an effective tool gene for genetic manipulation to improve the flavonol synthesis.

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The MYB transcription factor PbMYB12b positively regulates flavonol biosynthesis in pear fruit.

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