Fig. 6. Transient overexpression of CrMYB73 in transgenic N. tabacum leaves. The expression of CrMYB73 was driven by the CaMV 35S promoter. (A) Color changes after infiltration with empty vector (SK) and CrMYB73; (B) organic Torin 2 content in tobacco leaves; asterisks (*) indicate significant differences (p < 0.05), double asterisks (**) indicate significant differences (p < 0.01); (C) anthocyanin content in tobacco leaves.Figure optionsDownload full-size imageDownload as PowerPoint slide
The pH within the vacuole controls enzymatic reactions, protein sorting and stability of metabolites and relies on transporters which translocate protons and other ions across the tonoplast (Casey et al., 2010). The vacuole lumen is acidified mainly by V-ATPase and V-PPase, and some proton-coupled transporters, such as NHX-type antiporters (Reguera et al., 2015), and anion and cation exchangers are also involved in pH homeostasis (Schumacher, 2014).
Unlike the model plants, citrus is a perennial fruit and lacks a gene transformation system. Here, transient overexpression of CrMYB73 in N. tabacum leaves was conducted to verify gene function. CrMYB73 overexpression significantly elevated citric acid accumulation. This finding is similar to previous reports, for example, overexpression of petunia PhPH4 activated vacuolar acidification ( Quattrocchio et al., 2006). However, in that report the organic acid levels were not measured. In the present transient overexpression experiments, however, the relationship between CrMYB73 and citric acid content was verified, and one possible reasons for acidification highlighted.