The Role Of β-glucosidase Genes In Regulating Fruit Ripening And Endogenous ABA Level

The small molecules in plant exist in various forms in which the important and abundant one is the glycosylation form. The β-glucosidase which can catalyze the glycosylated small molecular are found universally in higher plants and plays various roles. There already have reports about the activation of abscisic acid by β-glucosidase in Arabidopsis thaliana, however, less study was about the role of β-glucosidase in the fruit ripening and ABA metabolism. This study analyzed the role of β-glucosidase genes in the fruits ripening and ABA metabolism in the non-climacteric fruits strawberry, watermelon and climacteric fruit tomato.The experimental results indicated that the transcript level of FaBG3was high and increased quickly in ripening progress of strawberry fruits. The strawberry fruit could not ripen normally after suppression of FaBG3gene expression. Considering the experimental results of dehydration and B. cinerea fungal infection of FaBG3-RNAi fruits, it seems that FaBG3gene might play roles in the strawberry fruit ripening and response to biotic/abiotic stresses. Three β-glucosidase genes CIBG1, CIBG2and CIBG3which had different expression patterns in watermelon fruit ripening progress were cloned and the CIBG2was induced by dehydration. Twenty GH family1BG genes were found and analysed in the climacteric fruit tomato to analyse the roles of β-glucosidase genes in tomato fruit ripening. The expression level of SIBG1increased dramatically in the breaker and turning stages and hybridization in situ results indicated that the SIBG1expressed mainly in style and ovule. After suppression of SIBG1expression, tomato fruits could not ripen normally and it influenced the expression levels of genes related to ethylene, IAA and carotenoid.In Arabidopsis thaliana there had already reports about the glycosylation of ABA. The P-glucosidase S1BG2in tomato was identified as the BG could catalyze ABA-GE to release free ABA. The results indicated that the expression level of SIBG2in pericarp was not changed obviously while in the seed it was increased during tomato fruit ripening stages. The hybridization in situ results indicated that the SIBG2expressed mainly in style and ovule. These results indicated that SIBG2might play a role in the seed maturation. The S1BG2was induced by ABA and dehydration. After dehydration, the expression of SIBG2in pericarp was increased dramatically while the one in seed was not changed. Consisdering the genes expression patterns in other metabolic pathways of ABA, it seems that SIBG2in pericarp might be more sensitive to dehydration stress and it might be the ABA main metabolic pathways to response the dehydration stress in seed. From the results it indicated that β-glucosidase genes play essential roles in the fruits development and ripening progress which might have a relationship with the catalysis ABA-GE. This study provide new theory evidence for the role of ABA in fruit ripening.