Abstract
In most grapevine planting regions, especially in south of China, plenty of rainfall and high water level underground are the characteristic of the area, a series of problem during fruit ripening easily caused poor color quality. Thereby affecting fruit quality, yield and economic benefits. The accumulation of anthocyanin is regulated by transcriptional regulatory factor and a series of cultivation measures, root restriction can make plants in the environment of stress and stress relief, root restriction induced the higher expression of VvMYB15 and VvWRKY40, and consistent with anthocyanin accumulation. Whether and how root restriction-inducible VvMYB15 and VvWRKY40 transcription factor regulate anthocyanin synthesis in grape berry is still unclear. In this study, we identified that the transient overexpression of VvMYB15 and VvWRKY40 alone or both in strawberry fruits and grape berries can promote anthocyanin accumulation and increase the expression level of anthocyanin biosynthetic genes, indicating VvMYB15 and VvWRKY40 play a positive regulator of anthocyanin biosynthesis. Furthermore, we confirmed that both VvMYB15 and VvWRKY40 specifically bind to the promoter region of VvF3′5′H and VvUFGT, and the expression of VvF3′5′H and VvUFGT is further activated through the heterodimer formation between VvMYB15 and VvWRKY40. Finally, we confirmed that VvMYB15 promoted anthocyanin accumulation by interacting with VvWRKY40 in grape berries, our findings provide insights into a mechanism involving the synergistic regulation of root restriction-dependent coloration and biosynthesis via a VvMYB15 and VvWRKY40 alone or both in grape berries.
Highlights
Color is an important fruit quality index that influence the purchasing behavior of consumers to some degree
Regarding to grape berry development, veraison was defined as the onset of ripening in which grape clusters began to color, in this study, almost no detectable anthocyanin in 40 and 50 days after anthesis (DAA), and anthocyanin accumulation was initiated at 60 DAA (Veraison), the grape berries were harvested at 110 DAA and total anthocyanin content of grape berry was significantly increased by root restriction, up to 3.2-fold compared with the control (Figure 1D), consistent with our visual appearances, supporting a role for root restriction in promoting anthocyanin accumulation
The results showed that the expression pattern of VvMYB15, VvF3 5 H, VvPAL, and VvCHS3 were sharply increased at veraison and gradually decreased until maturity and in parallel with the content of anthocyanin, the expression pattern of VvWRKY40, VvUFGT, VvF3H, and VvUFGT1 were strongest in post-veraison under root restriction, peaking at 80 DAA
Summary
Color is an important fruit quality index that influence the purchasing behavior of consumers to some degree. VvMYBPA1 did not activate the promoter of VvUFGT, which encodes the anthocyanin specific flavonoid-3O-glucosyltransferase, while activated the expression of VvLAR and VvANR and further regulate the proanthocyanidin synthesis, indicating that tissue and temporal-specific expression of VvANR and VvLAR correlates with proanthocyanidins (PAs) accumulation prior to veraison in grapes (Bogs et al, 2007). It was reported that the WRKY TFs PhPH3 in petunia correlates with change in the color of petals by playing a role in downstream of MBW complex, VvWRKY26, a homologous gene of PhPH3 in grape berry, induces the accumulation of flavonoids (Amato et al, 2017). QRTPCR and pH differential method revealed VvMYB15 alone or together with VvWRKY40 can activate the activity of anthocyanin biosynthesis structural genes in strawberry fruits or grape berries. Our research revealed a potential mechanism of regulating anthocyanin biosynthesis in colored grape berry, which will help elucidate the regulatory network to clarify anthocyanin accumulation in other species
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