Genome-wide identification of the oat MLO family and identification of a candidate AsMLO associated with powdery mildew susceptibility

Blumeria graminis f. spp. avenae is the causal agent of powdery mildew disease in oats (Avena sativa). It is the most significant limiting factor to oat production, with yield losses ranging from 5%-40%, during high disease pressure conditions. Certain members of the Mildew Locus O (MLO) gene family have been shown to act as powdery mildew susceptibility factors in many different plant species. A loss-of-function mutation of specific MLO genes confers broad-spectrum resistance against powdery mildew pathogens. Potential MLO candidates have not yet been identified in oats. In this study, we identified oat MLOs by querying 341 known MLO protein sequences against the publicly available oat genome. 11 MLO-like sequences were identified in oats. Phylogenetic analysis grouped these candidates into four different clades, one of which, AsMLO1 was grouped together with other cereal MLOs functionally known to contribute to powdery mildew susceptibility. AsMLO1 showed the highest similarity to the known powdery mildew-associated MLO proteins from wheat and barley. Gene expression analysis revealed AsMLO1 expression is up regulated at 12 hours post-infection with Bga and was inferred to be a candidate gene associated with powdery mildew susceptibility in oats. These results are an important step towards more durable strategies to control powdery mildew incidence and severity in oats.