Functional characterizations of β-glucosidases involved in aroma compound formation in tea (Camellia sinensis)

Tea (Camellia sinensis) aroma is an important factor affecting tea quality. Many tea aroma compounds are present as glycosidically conjugated forms in tea leaves, and can be hydrolyzed by beta-glucosidase (beta-Glu) and beta-primeverosidase to release free tea aromas. beta-Primeverosidase has been identified and functionally characterized, while beta-Glu has not been identified in tea leaves. In the present study, we established a yeast expression system to recombine CsGH1BG1, CsGH3BG1, and CsGH5BG1, which belonged to GH1, GH3, and GH5 families in plants, respectively. These three recombinant Cs beta-Glus hydrolyzed the beta-glucopyranosidically conjugated aromas to form free aromas, suggesting that there was no specific Cs beta-Glus for the hydrolysis of beta-glucopyranosidically conjugated aromas in vitro. Furthermore, subcellular localization of the Cs beta-Glus indicated that CsGH1BG1 and CsGH3BG1 were located in the cytosol and vacuole, respectively, while CsGH5BG1 was located in the cell wall. This suggested that CsGH1BG1 and CsGH3BG1 might be responsible for the hydrolysis of beta-glucopyranosidically conjugated aromas in tea leaves during the tea manufacturing process. This study provides the first evidence of Cs beta-Glus in tea leaves, and will advance understanding of tea aroma formation.