Variable responses of two VIMYBA gene promoters to ABA and ACC in Kyoho grape berries

The VIMYBA subfamily of transcription factors has been known to be the functional regulators in anthocyanin biosynthesis in red grapes. In this study, the expressions of the VIMYBAI-2 and VIMYBA2 genes, and the responses of the VIMYBAI-2/2 promoters to ABA and ACC treatments in Kyoho grape berries are examined through quantitative real-time PCR analysis and the transient expression assay. The results show that the expressions of VIMYBAI-2/2 increase dramatically after veraison and reach their highest levels when the berries are nearly fully ripe. Exogenous ABA promotes the expressions of VIMYBAI-2/2, whereas the ACC treatment increases the expression of VIMYBA2, however, it has no effect on VIMYBAI-2. The ABA treatment has a faster and stronger effect on berry pigmentation than ACC does. The VIMYBAI-2 promoter sequence contains two ABA response elements (ABRE) but no ethylene response element (ERE), whereas the VIMYBA2 promoter sequence contains two ABRE and one ERE in the upstream region of the start codon. The VIMYBA2 promoter can be activated by both ABA (more effective) and ACC, whereas the VIMYBAI-2 promoter can be activated by ABA only. In sum, ABA can promote the coloring of Kyoho grape by the promotion of VIMYBAI-2/2 transcriptions via activating the response of their promoters to ABA, whereas ethylene only regulates VIMYBA2 through the response activation of its promoter to ACC which partially enhances the coloring. (C) 2017 Elsevier GmbH. All rights reserved.