Overexpression of a Cytochrome P450 Monooxygenase Involved in Orobanchol Biosynthesis Increases Susceptibility to Fusarium Head Blight

Abstract

Fusarium Head Blight (FHB) is a cereal disease caused primarily by the ascomycete fungusFusarium graminearumwith public health issues due to the production of mycotoxins including deoxynivalenol (DON). Genetic resistance is an efficient protection means and numerous quantitative trait loci have been identified, some of them related to the production of resistance metabolites. In this study, we have functionally characterized theBrachypodium distachyon BdCYP711A29gene encoding a cytochrome P450 monooxygenase (CYP). We showed thatBdCYP711A29belongs to an oligogenic family of five members. However, following infection byF. graminearum,BdCYP711A29is the only copy strongly transcriptionally induced in a DON-dependent manner. The BdCYP711A29 protein is homologous to theArabidopsis thalianaMAX1 andOryza sativaMAX1-like CYPs representing key components of the strigolactone biosynthesis. We show that BdCYP711A29 is likely involved in orobanchol biosynthesis. Alteration of theBdCYP711A29sequence or expression alone does not modify plant architecture, most likely because of functional redundancy with the other copies.B. distachyonlines overexpressingBdCYP711A29exhibit an increased susceptibility toF. graminearum, although no significant changes in defense gene expression were detected. We demonstrate that both orobanchol and exudates ofBd711A29overexpressing lines stimulate the germination ofF. graminearummacroconidia. We therefore hypothesize that orobanchol is a susceptibility factor to FHB.