The role of hexokinases from grape berries (Vitis vinifera L.) in regulating the expression of cell wall invertase and sucrose synthase genes
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The activity and content of hexokinases (HXKs) had an inverse relationship with glucose and/or fructose levels during grape berry development. HXK subcellular localization was investigated in grape berry.
In plants, hexokinase (HXK, EC 188.8.131.52) involved in hexose phosphorylation, plays an important role in sugar sensing and signaling. In this study, we found that at Phase I of grape berry development, lower hexose (glucose or fructose) levels were concomitant with higher HXK activities and protein levels. After the onset of ripening, we demonstrated a drastic reduction in HXK activity and protein levels accompanied by a rising hexose level. Therefore, our results revealed that HXK activity and protein levels had an inverse relationship with the endogenous glucose or fructose levels during grape berry development. A 51 kDa HXK protein band was detected throughout grape berry development. In addition, HXK located in the vacuoles, cytoplasm, nucleus, proplastid, chloroplast, and mitochondrion of the berry flesh cells. During grape berry development, HXK transcriptional level changed slightly, while cell wall invertase (CWINV) and sucrose synthase (SuSy) expression was enhanced after véraison stage. Intriguingly, when sliced grape berries were incubated in different glucose solutions, CWINV and SuSy expression was repressed by glucose, and the intensity of repression depended on glucose concentration and incubation time. After sliced, grape berries were treated with different glucose analogs, CWINV and SuSy expression analyses revealed that phosphorylation of hexoses by hexokinase was an essential component in the glucose-dependent CWINV and SuSy expression. In the meantime, mannoheptulose, a specific inhibitor of hexokinase, blocked the repression induced by glucose on CWINV and SuSy expression. It suggested that HXK played a major role in regulating CWINV and SuSy expression during grape berry development.
KeywordsCell wall invertase Hexokinase Grape berry Sucrose synthase Sugar
Cell wall invertase
Day after full bloom
The authors are most grateful to Prof. Sheen J. (Harvard Medical School Department of Molecular Biology, 185 Cambridge St., CPZN7624E, Massachusetts General Hospital, Boston, MA, 02114, USA) for her providing us HXK polyclonal antibody. This research was supported by the National Natural Science Foundation of China (Grant Nos. 30871698, 31372036, and 31071764).
Conflict of interest
The authors declare no conflict of interest.
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