Abstract: Glycosylation plays a pivotal role in determining the diversities of plant small molecules. Glycosyltransferases are ubiquitous proteins involved in such reactions. However, the exact mechanisms of sugar donor or acceptor substrate recognition are still to be elusive. We reported the isolation of a new glycosyltransferase gene from blackberry plants(Rubus spp.), nominated as UGT78H2(GenBank Accession No.:KM061379) by the international UDP Glucosyltransferase Nomenclature Committee. The full length of the gene contained an open reading frame of 1 380 nucleotides, encoding a 50.6 kD polypeptides of 459 amino acids. By further analysis, the deduced enzyme was a typical family-1 glucosyltransferase with the plant secondary product glucosyltransferase signature motif in the C terminal. Phylogenetic trees revealed the clustering of UGT78H2 in the F node together with other Arabidopsis thaliana GTs, inferring the possible catalysis activity toward flavonoid compounds. Amino acids of UGT78H2 shared most, but only 88% identity to the RhUF3GT(UGT78H1) in Rose hybrid when aligned to other glycosyltransferases. Most abundant transcripts of the gene were observed in the immature blackberry fruits, a stage when little anthocyanins were produced. Additionally, transcription levels decreased dramatically with the maturation of fruits. We used the Medicago truncatula UGT78G1(PDB: 3HBF) as a template to homologically model the protein of UGT78H2 that was subsequently docked with 12 common flavonoid molecules. UGT78H2 was predicted to be a glucosyltransferase having maximum binding affinity towards quercetin, tangeritin and epicatechin.

Key words: blackberry, UGT78H2, cloning, flavonoids, molecular docking