Comparative and Functional Genomics Analysis of the Magnaporthales

The order Magnaporthales includes fungi of great economic importance that cause disease in cereal and turf grasses: Magnaporthe oryzae (rice blast), Gaeumannomyces graminis var. tritici (take-all disease), and Magnaporthe poae (summer patch disease). A genome-scale comparative study was conducted across 74 fungal genomes. Gene clusters involved in transcriptional regulation and enzymatic activities were highly represented in order specific clusters and the species specific genes, suggesting that such proteins may be more plastic and may contribute to speciation. No correlations between diversifying or purifying selection and distance to repetitive elements or an increased rate of evolution in secreted and small secreted proteins were observed. Thus no evidence was found to suggest multi-speed genome evolution or that proximity to repetitive elements plays a role in diversification of genes. Functional analysis was conducted on candidate effectors (small secreted proteins) identified from comparative genome analysis of 40 M. oryzae strains, transcriptome and proteome data. Through a forward genetics screen, 11 suppressors of plant cell death (SPD) were found to inhibit the host cell death reaction induced by the BAX and/or the NPP1 genes within N. benthamiana.  Four were previously identified as either essential for pathogenicity of M. oryzae, secreted into the plant during disease development, or homologues of other characterized suppressors.  The others are novel and all remain to be fully characterized.