Functional characterization of a maize UDP-glucosyltransferase involved in the biosynthesis of flavonoid 7-O-glucosides and di-O-glucosides

Plant Physiol Biochem. 2025 Apr:221:109583. doi: 10.1016/j.plaphy.2025.109583. Epub 2025 Jan 30.

Abstract

Flavonoids are glycosylated in the final steps of their synthesis by UDP-dependent glycosyltransferase enzymes. We present the functional characterization of the first maize flavonoid O-glucosyltransferase enzyme from family 85, which exhibits properties not previously described. ZmUGT85W2 catalyzes the O-glucosylation of flavonols, flavones and flavanones, to form primarily 7-O-glucosides, but also flavonol O-glucoside positional isomers, flavones and flavonol di-O-glucosides. ZmUGT85W2 exhibited a differential kinetic behavior depending on the flavonoid acceptor, showing hyperbolic dependence for flavonols and sigmoidal response for flavanones and flavones. Structural and molecular docking analyses predicted conserved residues interacting with the sugar donor, with close contact with the 7-hydroxyl of the flavonoid acceptors, consistent with enzymatic activity results. In addition, ZmUGT85W2 is induced by UV-B radiation, and its expression is controlled by the B and PL1 transcription factors. Consistently, higher levels of flavone and flavonol O-glycosides are accumulated in leaves of plants exposed to solar UV-B compared to control plants, suggesting that ZmUGT85W2 is involved in the biosynthesis of these metabolites in maize leaves, contributing to UV-B tolerance. The activity of ZmUGT85W2, along with its elevated expression in silks and pericarps expressing the R2R3-MYB transcription factor P1, highlights its critical role in the accumulation of flavonoid O-glucosides in these tissues. Together, our findings reveal a key step in maize flavonoid O-glycosides biosynthesis, with the observed positive cooperative behaviors suggesting that ZmUGT85W2 plays a crucial role in finely regulating metabolic flux towards these compounds in planta.

Keywords: Enzyme kinetics; Flavonoid; Gene expression; Maize; Regioselectivity; UDP-Dependent glycosyltransferase; UV-B radiation.

MeSH terms

  • Flavonoids* / biosynthesis
  • Gene Expression Regulation, Plant
  • Glucosides* / biosynthesis
  • Glucosides* / metabolism
  • Glucosyltransferases* / genetics
  • Glucosyltransferases* / metabolism
  • Molecular Docking Simulation
  • Plant Proteins* / genetics
  • Plant Proteins* / metabolism
  • Zea mays* / enzymology
  • Zea mays* / genetics
  • Zea mays* / metabolism

Substances

  • Glucosyltransferases
  • Flavonoids
  • Glucosides
  • Plant Proteins