Characterization of a bifunctional C-/O-glycosyltransferase from maize

MARÍA LORENA FALCONE FERREYRA, MARÍA ISABEL CASAS, ERICH GROTEWOLD, PAULA CASATI, AND EDUARDO RODRIGUEZ

Mendoza

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Investigadores en Bioquímica y Biología Molecular (SAIB); 2012

Sociedad Argentina de Investigadores en Bioquímica y Biología Molecular (SAIB)

Flavonoids are accumulated in the vacuoles as O-glycosylated derivatives; however, several species including cereals synthesize flavonoid C-glycosides. Maysin is the C-glycosyl flavone that predominates in silks of some maize varieties conferring resistance to lepidopteran insects. The transcription factor R2R3-MYB P1 is the main QTL responsible for its production. Recently, we demonstrated that ZmF2H1, which expression is highly regulated by P1, encodes a flavanone 2-hydroxylase, which converts flavanones to 2-hydroxy derivatives. In order to identify a C-glycosyltransferase involved in the formation of maysin, we isolated the cDNA coding for ZmUGT5 and its activity was characterized by in vivo and in vitro assays followed by identification of the products formed by LC-MS. In vivo activity assays in yeast co-expressing ZmF2H1 and ZmUGT5 showed the formation of flavones C-glycosides from flavanones, being 2-hydroxy flavanones generated by ZmF2H1 activity the substrate acceptors for ZmUGT5 C-glycosyltransferase activity. Surprisingly, ZmUGT5 can also O-glycosylate flavanones in bioconversion assays in E. coli as well as by in vitro assays with the purified recombinant protein. The results described show that ZmUGT5 is the first bifunctional glycosyltransferase that can form both C-glycoside and O-glycoside using natural substrates such as flavonoids. Its role in the biosynthesis of maysin is discussed.