Isolation of anthocyanin 7-O-glucosyltransferase from Canterbury bells (Campanula medium)

摘要

Canterbury bells ( Campanula medium ) have deep purple petals due to the accumulation of 7-polyacylated anthocyanin molecules. The first step in the production of 7-polyacylated anthocyanins is glucosylation at the C7 position of anthocyanidin mediated by an acyl-glucose dependent anthocyanin 7- O -glucosyltransferase (AA7GT). To date, two such enzymes have been identified: DgAA7GT from delphinium ( Delphinium grandiflorum ) and AaAA7GT from African lily ( Agapanthus africanus ). Here, we describe the isolation of AA7GT cDNA from C. medium and the characterization of the enzymatic properties of a recombinant protein. The CmAA7GT protein belongs to glycoside hydrolase family 1, similarly to other AA7GTs; a phylogenetic analysis revealed that CmAA7GT was in the same clade as other AA7GTs. The CmAA7GT gene showed expression only in flowers, with a peak level of expression at the middle stage of floral development. A recombinant CmAA7GT protein showed significant preference for interaction with anthocyanidin 3- O -rutinoside rather than anthocyanidin 3- O -monoglycoside, which is the preferred target of other AA7GTs. This difference in target preference may reflect a conformational difference in the acceptor pocket of the enzyme protein that recognizes the anthocyanidin glycoside.