The use of a photoactivatable kaempferol analogue to probe the role of flavonol 3-O-galactosyltransferase in pollen germination

Abstract

Flavonol induced pollen germination in petunia is rapid, specific, and achieved at low concentrations of kaempferol or quercetin. To determine the macromolecules that interact with the flavonol signal we have synthesized affinity-tagged kaempferol analogues. The first generation molecules are based on a benzophenone photophore. We find that 2-(3-benzoylphenyl)-3,5,7-trihydroxychromen-4-one (BPKae) antagonizes flavonol-induced pollen germination in a concentration-dependent manner. Further, BPKae acts as an irreversible inhibitor of flavonol 3-O-galactosyltransferase (F3GalTase), the gametophyte-specific enzyme that controls the accumulation of glycosylated flavonols in pollen. The effects of BPKae are mediated by UV-A light treatment. The binding characteristics of BPKae to F3GalTase suggest that it can be used to identify the residues required for flavonol-binding and catalysis.