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Open Access Research

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

Yeonyee Oh1, Nicole Donofrio13, Huaqin Pan14, Sean Coughlan2, Douglas E Brown1, Shaowu Meng1, Thomas Mitchell15 and Ralph A Dean1*

Author Affiliations

1 North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA

2 Agilent Technologies, Little Falls, DE 19808-1644, USA

3 Current address: University of Delaware, Department of Plant and Soil Science, Newark, DE 19716, USA

4 Current address: RTI international, Research Triangle Park, NC 27709-2194, USA

5 Current address: Ohio State University, Department of Plant Pathology, Columbus, OH 43210, USA

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Genome Biology 2008, 9:R85  doi:10.1186/gb-2008-9-5-r85

Published: 20 May 2008

Abstract

Background

Rice 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.

Results

We 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.

Conclusion

We 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.