Abstract
The R2R3 MYB genes associated with the flavonoid/anthocyanidin pathway feature two repeats, and represent the most abundant classes of MYB genes in plants; however, the physiological role and regulatory function of most R2R3 MYBs remain poorly understood in kiwifruit (Actinidia). Here, genome-wide analysis identified 155 R2R3-MYBs in the ‘Red 5′ version of the Actinidia chinensis genome. Out of 36 anthocyanin-related AccR2R3-MYBs, AcMYB10 was the most highly expressed in inner pericarp of red-fleshed kiwifruit. The expression of AcMYB10 was highly correlated with anthocyanin accumulation in natural pigmentation during fruit ripening and light-/temperature-induced pigmentation in the callus. AcMYB10 is localized in the nuclei and has transcriptional activation activity. Overexpression of AcMYB10 elevates anthocyanin accumulation in transgenic A. chinensis. In comparison, A. chinensis fruit infiltrated with virus-induced gene silencing showed delayed red coloration, lower anthocyanin content, and lower expression of AcMYB10. The transient expression experiment in Nicotiana tabacum leaves and Actinidia arguta fruit indicated the interaction of AcMYB10 with AcbHLH42 might strongly activate anthocyanin biosynthesis by activating the transcription of AcLDOX and AcF3GT. In conclusion, this study provides novel molecular information about R2R3-MYBs in kiwifruit, advances our understanding of light- and temperature-induced anthocyanin accumulation, and demonstrates the important function of AcMYB10 in the biosynthesis of anthocyanin in kiwifruit.
Highlights
MYB transcription factors (TFs) are found in a wide range of higher plants and constitute one of the largest transcription factor families
This study aimed to characterize the candidate R2R3-MYBs involved in the accumulation of anthocyanin in kiwifruit and to understand how the regulatory network of anthocyanin biosynthesis is affected by light and temperature
Because cyanidins are the main anthocyanin in A. chinensis responsible for the red color [12], these results indicate that the overexpression of AcMYB10 promotes the biosynthesis of metabolites in the cyanidin pathway, leading to the red color of transgenic young leaves of OE
Summary
MYB transcription factors (TFs) are found in a wide range of higher plants and constitute one of the largest transcription factor families. They are characterized by a structurally conserved DNA-binding domain that consists single or multiple imperfect repeats located near the N-terminus. These repeats function synergistically or individually in DNA binding and protein–protein interactions, respectively [1]. The first plant MYB gene, C1, was isolated from maize (Zea mays), and encodes a c-MYB-like protein involved in the anthocyanin biosynthesis pathway [6]. R2R3-MYBs were reported to contribute to regulation of anthocyanin accumulation in Arabidopsis, grape (Vitis vinifera), Asian pear (Pyrus pyrifolia), and apple (Malus domestica) [7,8,9,10]
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