Huaqin Pan

The genome sequence of the rice blast fungus Magnaporthe grisea

Magnaporthe grisea is the most destructive pathogen of rice worldwide and the principal model organism for elucidating the molecular basis of fungal disease of plants. Here, we report the draft sequence of the M. grisea genome. Analysis of the gene set provides an insight into the adaptations required by a fungus to cause disease. The genome encodes a large and diverse set of secreted proteins, including those defined by unusual carbohydrate-binding domains. This fungus also possesses an expanded family of G-protein-coupled receptors, several new virulence-associated genes and large suites of enzymes involved in secondary metabolism. Consistent with a role in fungal pathogenesis, the expression of several of these genes is upregulated during the early stages of infection-related development. The M. grisea genome has been subject to invasion and proliferation of active transposable elements, reflecting the clonal nature of this fungus imposed by widespread rice cultivation.

Novel G-protein-coupled receptor-like proteins in the plant pathogenic fungus Magnaporthe grisea

BackgroundThe G-protein-coupled receptors (GPCRs) are one of the largest protein families in human and other animal genomes, but no more than 10 GPCRs have been characterized in fungi. Do fungi contain only this handful or are there more receptors to be discovered? We asked this question using the recently sequenced genome of the fungal plant pathogen Magnaporthe grisea.ResultsProteins with significant similarity to fungus-specific and other eukaryotic GPCRs were identified in M. grisea. These included homologs of known fungal GPCRs, the cAMP receptors from Dictyostelium, and a steroid receptor mPR. We also identified a novel class of receptors typified by PTH11, a cell-surface integral membrane protein required for pathogenicity. PTH11 has seven transmembrane regions and an amino-terminal extracellular cysteine-rich EGF-like domain (CFEM domain), a characteristic also seen in human GPCRs. Sixty-one PTH11-related proteins were identified in M. grisea that shared a common domain with homologs in Neurospora crassa and other fungi belonging to this subphylum of the Ascomycota (the Pezizomycotina). None was detected in other fungal groups (Basidiomycota or other Ascomycota subphyla, including yeasts) or any other eukaryote. The subclass of PTH11 containing the CFEM domain is highly represented in M. grisea.ConclusionIn M. grisea we identified homologs of known GPCRs and a novel class of GPCR-like receptors specific to filamentous ascomycetes. A member of this new class, PTH11, is required for pathogenesis, thus suggesting roles in pathogenicity for other members. The identified classes constitute the largest number of GPCR-like proteins reported in fungi to date.

Transcriptome analysis reveals new insight into appressorium formation and function in the rice blast fungus Magnaporthe oryzae

BackgroundRice blast disease is caused by the filamentous Ascomycetous fungus Magnaporthe oryzae and results in significant annual rice yield losses worldwide. Infection by this and many other fungal plant pathogens requires the development of a specialized infection cell called an appressorium. The molecular processes regulating appressorium formation are incompletely understood.ResultsWe analyzed genome-wide gene expression changes during spore germination and appressorium formation on a hydrophobic surface compared to induction by cAMP. During spore germination, 2,154 (approximately 21%) genes showed differential expression, with the majority being up-regulated. During appressorium formation, 357 genes were differentially expressed in response to both stimuli. These genes, which we refer to as appressorium consensus genes, were functionally grouped into Gene Ontology categories. Overall, we found a significant decrease in expression of genes involved in protein synthesis. Conversely, expression of genes associated with protein and amino acid degradation, lipid metabolism, secondary metabolism and cellular transportation exhibited a dramatic increase. We functionally characterized several differentially regulated genes, including a subtilisin protease (SPM1) and a NAD specific glutamate dehydrogenase (Mgd1), by targeted gene disruption. These studies revealed hitherto unknown findings that protein degradation and amino acid metabolism are essential for appressorium formation and subsequent infection.ConclusionWe present the first comprehensive genome-wide transcript profile study and functional analysis of infection structure formation by a fungal plant pathogen. Our data provide novel insight into the underlying molecular mechanisms that will directly benefit efforts to identify fungal pathogenicity factors and aid the development of new disease management strategies.

The role of transposable element clusters in genome evolution and loss of synteny in the rice blast fungus Magnaporthe oryzae.

BackgroundTransposable elements are abundant in the genomes of many filamentous fungi, and have been implicated as major contributors to genome rearrangements and as sources of genetic variation. Analyses of fungal genomes have also revealed that transposable elements are largely confined to distinct clusters within the genome. Their impact on fungal genome evolution is not well understood. Using the recently available genome sequence of the plant pathogenic fungus Magnaporthe oryzae, combined with additional bacterial artificial chromosome clone sequences, we performed a detailed analysis of the distribution of transposable elements, syntenic blocks, and other features of chromosome 7.ResultsWe found significant levels of conserved synteny between chromosome 7 and the genomes of other filamentous fungi, despite more than 200 million years of divergent evolution. Transposable elements are largely restricted to three clusters located in chromosomal segments that lack conserved synteny. In contradiction to popular evolutionary models and observations from other model organism genomes, we found a positive correlation between recombination rate and the distribution of transposable element clusters on chromosome 7. In addition, the transposable element clusters are marked by more frequent gene duplications, and genes within the clusters have greater sequence diversity to orthologous genes from other fungi.ConclusionTogether, these data suggest that transposable elements have a profound impact on the M. oryzae genome by creating localized segments with increased rates of chromosomal rearrangements, gene duplications and gene evolution.