The role of hexokinases from grape berries (Vitis vinifera L.) in regulating the expression of cell wall invertase and sucrose synthase genes

Abstract

In plants, hexokinase (HXK, EC 2.7.1.1) 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.

Infection of post-harvest peaches by Monilinia fructicola accelerates sucrose decomposition and stimulates the Embden–Meyerhof–Parnas pathway

“…This implies that peaches inoculated with fungi increase their energy supply by decomposing sucrose to yield hexose, which is channeled through HXK, PK, and PFK into EMP. HXK can respond to biotic and abiotic stress in plants 43–45 . In Arabidopsis , the expression of HXK2 responses to cold and salt stress 44 .…”

Molecular candidates for early-stage flower-to-fruit transition in stenospermocarpic table grape (Vitis vinifera L.) inflorescences ascribed by differential transcriptome and metabolome profiles

“…8) may affect expression of different genes, such as encoding sugar transporters, components of the photosystems, enzymes of carbohydrate metabolism, enzymes of secondary metabolism, and transcription factors [59]. The regulation of HEXOKINASE-1 (VIT 09s0002g03390) (Table 4) was reported to be involved in sugar-sensing and signalling through CW invertase and sucrose synthase regulation [75] and sugar control of transporters [59] in grape berries. Here, we can associate this regulation with early stages of fruit set in grapevine, during which hexose sugar signals that regulate the cell cycle and cell division programmes seemed to be generated [76].…”

Structure, Expression, and Functional Analysis of the Hexokinase Gene Family in Cassava

“…For instance, HXK1 and HXK2 from Vitis vinifera play major roles in regulating the gene expression of cell wall invertases and sucrose synthases ( SuSy1 and SuSy2 ) during grape berry development. These enzymes are involved in sucrose phloem unloading and the control of carbohydrate accumulation in sink tissues [22]. The expression of the granule-bound starch synthase gene OsGBSSII from O. sativa is dependent on the sugar-regulating pathway of HXKs [23].…”