Secondary product glycosyltransferases in seeds of Brassica napus

This study describes a systematic screen for secondary product UDP-glycosyltransferases (UGTs; EC 2.4.1) involved in seed development of oilseed rape (Brassica napus) and was aimed at identifying genes related to UGT84A9 encoding UDP-glucose: sinapate glucosyltransferase (EC 2.4.1.120), a proven target for molecular breeding approaches to reduce the content of anti-nutritive sinapate esters. By RT-PCR with primers recognizing the conserved signature motif of UGTs, 13 distinct ESTs could be generated from seed RNA. Sequence analysis allowed to assign the isolated ESTs to groups B, D, E, and L of the UGT family. In an alternative approach, two open reading frames related to UGT84A9 were cloned from the B. napus genome and designated as UGT84A10 and UGT84A11, respectively. Functional expression of UGT84A10 revealed that the encoded enzyme catalyzes the formation of 1-O-acylglucosides (beta-acetal esters) with several hydroxycinnamates whereas, in our hands, the recombinant UGT84A11 did not display this enzymatic activity. Semi-quantitative RT-PCR confirmed that the majority of potential UGTs specified by the isolated ESTs is differentially expressed. A pronounced transcriptional up-regulation during seed development was evident for UGT84A9 and one EST (BnGT3) clustering in group E of UGTs. UGT84A10 was highly induced in flowers and expressed to a moderate level in late seed maturation indicating a possible involvement in seed-specific sinapate ester biosynthesis.