The use of abscisic acid analogues to analyse the substrate selectivity of UGT71B6, a UDP-glycosyltransferase of Arabidopsis thaliana

This study analyses the activity of an Arabidopsis thaliana UDP-glycosyltransferase, UGT71B6 (71B6), towards abscisic acid (ABA) and its structural analogues. The enzyme preferentially glucosylated ABA and not its catabolites. The requirement for a specific chiral configuration of (+)-ABA was demonstrated through the use of analogues with the chiral centre changed or removed. The enzyme was able to accommodate extra bulk around the double bond of the ABA ring but not alterations to the 8'- and 9'-methyl groups. Interestingly, the ketone of ABA was not required for glucosylation. Bioactive analogues, resistant to 8'-hydroxylation, were also poor substrates for conjugation by UGT71B6. This suggests the compounds may be resistant to both pathways of ABA inactivation and may, therefore, prove to be useful agrochemicals for field applications.