EVOLUTIONARY CONSERVATION AND FUNCTIONAL CHARACTERIZATION OF PATHOGEN-RESPONSIVE MLO GENE PROMOTER SIGNATURES

A new challenge in the post-genomic era is the discovery of fundamental principles governingbiological responses. Powdery mildew (PM) is a widespread plant disease of temperate climatesthat is caused by ascomycete fungi of the order Erysiphales. It is an important threat to agricultureand can cause significant harvest losses. Specific homologs of the MLO gene family are PMsusceptibility factors, as their loss-of function results in PM durable resistance (mlo resistance) inseveral plant species. However, the actual role of MLO genes in plant-pathogen interactions is stillnot clear. One step towards this direction is the understanding of the regulation of MLO genes at thegenome level. We carried out a genome-wide characterization of the MLO gene family in twentythreeplant and two alga genomes. Evolutionary history and phylogenetic relationships of thisimportant gene family in plant king-domain were studied through maximum likelihood analysis. Inaddition, we investigated the structure of Putative Promoter Regions (PPRs) of MLO homologsextracted from 25 genomes, in search for putative regulatory elements in pathogen-responsive MLOgenes. A unique motif arrangement for each MLO phylogenetic clade was delineated albeit a highlyconserved regulatory element core was found in all MLOs. Two over-represented motifs (Thyminerichmotif and TC box-like) in the PPRs of the upregulated MLO genes upon infection with PMfungi were found. The expression of three Cucurbitaceae genes containing the motifs abovementioned resulted strongly upregulated upon infection with the PM fungus. Our findings may helpto address further biological questions concerning the evolution and function of MLO genes. Thesilencing or a loss-of-function mutation in one or more of these candidate genes can lead to PMresistance through a genome engineering approach. Moreover, data reported here could beconveniently used by breeding research, aiming to develop powdery mildew resistant crops.