The Identification of Maize and Arabidopsis Type I FLAVONE SYNTHASEs Links Flavones with Hormones and Biotic Interactions

FALCONE FERREYRA ML; EMILIANI J; RODRIGUEZ EJ; CAMPOS BERMUDEZ VA; GROTEWOLD E; CASATI P

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Lugar: Rockville; Año: 2015 vol. 169 p. 1090 - 1107

0032-0889

Flavones are a major group of flavonoids with diverse functions and are extensively distributed in land plants. There are twodifferent classes of FLAVONE SYNTHASE (FNS) enzymes that catalyze the conversion of the flavanones into flavones. The FNSIclass comprises soluble Fe2+/2-oxoglutarate-dependent dioxygenases, and FNSII enzymes are oxygen- and NADPH-dependentcytochrome P450 membrane-bound monooxygenases. Here, we describe the identification and characterization of FNSI enzymesfrom maize (Zea mays) and Arabidopsis (Arabidopsis thaliana). In maize, ZmFNSI-1 is expressed at significantly higher levels in silksand pericarps expressing the 3-deoxy flavonoid R2R3-MYB regulator P1, suggesting that ZmFNSI-1 could be the main enzyme forthe synthesis of flavone O-glycosides. We also show here that DOWNY MILDEW RESISTANT6 (AtDMR6), the Arabidopsishomologous enzyme to ZmFNSI-1, has FNSI activity. While dmr6 mutants show loss of susceptibility to Pseudomonas syringae,transgenic dmr6 plants expressing ZmFNSI-1 show similar susceptibility to wild-type plants, demonstrating that ZmFNSI-1 cancomplement the mutant phenotype. AtDMR6 expression analysis showed a tissue- and developmental stage-dependent pattern,with high expression in cauline and senescing leaves. Finally, we show that Arabidopsis cauline and senescing leaves accumulateapigenin, demonstrating that Arabidopsis plants have an FNSI activity involved in the biosynthesis of flavones. The resultspresented here also suggest cross talk between the flavone and salicylic acid pathways in Arabidopsis; in this way, pathogenswould induce flavones to decrease salicylic acid and, hence, increase susceptibility.