Abstract
In this work, four vacuolar H+-PPase (VHP) genes were identified in the grape genome. Among them, VvVHP1; 2 was strongly expressed in berry skin and its expression exhibited high correlations to anthocyanin content of berry skin during berry ripening and under ABA and UVB treatments. VvVHP1; 2 was transcriptionally activated directly by VvMYBA1, and VvVHP1; 2 overexpression promoted anthocyanin accumulation in berry skins and Arabidopsis leaves; therefore, VvVHP1; 2 mediated VvMYBA1-regulated berry pigmentation. On the other hand, RNA-Seq analysis of WT and transgenic berry skins revealed that carbohydrate metabolism, flavonoid metabolism and regulation and solute carrier family expression were the most clearly altered biological processes. Further experiments elucidated that VvVHP1; 2 overexpression up-regulated the expression of the genes related to anthocyanin biosynthesis and transport via hexokinase-mediated glucose signal and thereby promoted anthocyanin accumulation in berry skins and Arabidopsis leaves. Additionally, modifications of sugar status caused by enhanced hexokinase activities likely play a key role in VvVHP1; 2-induced sugar signaling.
Highlights
There are two phylogenetically distinct H+-PPases in plant cells
Using Arabidopsis thaliana AtVHPs as reference sequences, 4 counterparts were found in the grape genome, i.e., VIT_09s0002g07880, VIT_11s0118g00350, VIT_14s0060g01280 and VIT_09s0054g00700, designated VvVHP1;1, VvVHP1; 2, VvVHP1;3 and VvVHP2, respectively, in light of their sequence similarity to their Arabidopsis counterparts (Figure 1A)
The results showed that the transcripts of VvVHP1; 2 and GUS activity were positively regulated by VvMYBA1 (Figures 5D–F)
Summary
There are two phylogenetically distinct H+-PPases in plant cells. Type I H+-PPases are K+ sensitive, and type II H+-PPases are K+ insensitive but extremely Ca2+ sensitive. Plant type I H+-PPases are usually located on the vacuolar membrane and are considered to be bona fide vacuolar markers (Rea et al, 1992; Maeshima, 2000); they are named vacuolar H+PPases (VHPs). Increasing evidence indicates that VHPs are localized on the plasma membrane of phloem cells in Arabidopsis and other plant species (Khadilkar et al, 2016; Regmi et al, 2016); greater localization of AVP1 at the vacuolar membrane compared with the plasma membrane has been reported (Segami et al, 2014). VHP1 enzyme consists of a single 80 kDa polypeptide (Maeshima, 2000). Type I VHPs and H+-ATPase have been predicted to be the key enzyme for vacuolar acidification
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