The Citrus transcription factor, CitERF13, regulates citric acid accumulation via a protein protein interaction with the vacuolar proton pump, CitVHA c4
Organic acids are essential to fruit flavor. The vacuolar H+ transporting adenosine triphosphatase (V ATPase) plays an important role in organic acid transport and accumulation. However, less is known of V ATPase interacting proteins and their relationship with organic acid accumulation. The relationship between V ATPase and citric acid was investigated, using the citrus tangerine varieties 'Ordinary Ponkan (OPK) and an early maturing mutant 'Zaoshu Ponkan (ZPK) Five V ATPase genes (CitVHA) were predicted as important to citric acid accumulation. Among the genes, CitVHA c4 was observed, using a yeast two hybrid screen, to interact at the protein level with an ethylene response factor, CitERF13. This was verified using bimolecular fluorescence complementation assays. A similar interaction was also observed between Arabidopsis AtERF017 (a CitERF13 homolog) and AtVHA c4 (a CitVHA c4 homolog) A synergistic effect on citric acid levels was observed between V ATPase proteins and interacting ERFs when analyzed using transient over expression in tobacco and Arabidopsis mutants. Furthermore, the transcript abundance of CitERF13 was concomitant with CitVHA c4. CitERF13 or AtERF017 over expression leads to significant citric acid accumulation. This accumulation was abolished in an AtVHA c4 mutant background. ERF VHA interactions appear to be involved in citric acid accumulation, which was observed in both citrus and Arabidopsis.
Scientific reports