Characterization of the MLO gene family in Rosaceae and gene expression analysis in Malus domestica

Powdery mildew (PM) is a major fungal disease for thousands of plant species, including many cultivated Rosaceae. Specific homologs of the MLO gene family act as PM-susceptibility genes, as their loss-of-function mutations grant durable and broad-spectrum resistance. PM pathogenesis is associated to a pathogendependent up-regulation of MLO genes during early stages of infection, causing down-regulation of plant defense pathways. We carried out a genome-wide characterization of the MLO gene family in apple, peach and strawberry, and we isolated apricot MLO homologs through a PCR-approach. Evolutionary relationships between MLO homologs were studied and syntenic blocks constructed. Homologs that are candidates for being PM susceptibility genes were inferred by phylogenetic relationships with functionally characterized MLO genes and, in apple, by monitoring their expression following inoculation with the PM causal pathogen Podosphaera leucotricha. Genomic tools available for Rosaceae were exploited in order to characterize the MLO gene family. Candidate MLO susceptibility genes were identified. In follow-up studies it can be investigated whether silencing or a lossof-function mutation in one or more of these candidate genes leads to PM resistance