Analyses of the fructokinase activity and its gene expression during the development of longan fruits

Objective Changes in the contents of sucrose, glucose and fructose, the activity of fructokinase (FRK) and its gene expression during the development of longan (Dimocarpus longan Lour.cv. Shixia) fruit aril were studied.

Method Sugar contents were determinated using HPLC, and the FRK activity was analyzed using colorimetric method.Real-time qPCR was used to analyze the expression of DlFRK gene.Prokaryotic expression vector was constructed using in-fusion method to express DlFRK gene in Escherichia coli Rosetta (DE3).

Result and conclusion The results showed that the contents of sucrose, glucose and fructose in the aril increased gradually with the development of longan fruits, and they tended to become stable at the mature stage.The fructokinase activity decreased gradually from 25.97 μmol·g^-1·h^-1to 13.18 μmol·g^-1·h^-1 at the early stages before maturation, and increased during maturation to 22.44 μmol·g^-1·h^-1 at full maturity.Quantitative RT-PCR analyses showed that the expression of fructokinase gene was relatively stable at the early stages, but it declined during the aril expanding period with a rapid sugar accumulation.The result of SDS-PAGE showed that pET-32a-DlFRK prokaryotic expression vector has been constructed.Gene expression has been successfully induced by IPTG in E.coil BL21.