Enzymatic and functional analysis of-glucosidase FaBG1 during strawberry fruit ripening

SummaryWhether or not βglucosidase is active in fleshy fruit remains unknown. We investigated levels of gene expression, enzyme activities, and the physiological functions of βglucosidase 1 (FaBG1) in strawberry (Fragaria ananassa Duch.) fruit flesh. Real-time RT-PCR analysis showed that concomitant with the onset of fruit colour development in strawberry, levels of expression of the βglucosidase 1 gene (FaBG1) increased rapidly. Furthermore, 15 mM histamine, an inhibitor of βglucosidase, significantly inhibited red-colour development in strawberry fruit. These results suggest that FaBG1 might play a role in strawberry fruit ripening. A combination of enzyme incubation assays with receptacle tissue and GC-MS analysis demonstrated that the red-colour in strawberry fruit was rich in abscisic acid (ABA)-glucosyl ester (ABA-GE) and that FaBG1 had high glycosyl hydrolase activity, which could promote the accumulation of free ABA via hydrolysis of ABA-GE. Using tobacco rattle virus (TRV)-induced gene silencing (VIGS), down-regulation of FaBG1 gene expression not only inhibited strawberry fruit ripening, but also led to a significant decline in ABA concentration in VIGS-treated fruit. In conclusion, these results provide physiological, biochemical, and molecular evidence to validate the hypothesis that strawberry βglucosidase 1 (FaBG1) has high glycosyl hydrolase activity and plays a role in fruit ripening via the rapid production of free ABA.