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A Putative MAP Kinase Kinase Kinase, MCK1, Is Required for Cell Wall Integrity and Pathogenicity of the Rice Blast Fungus, Magnaporthe oryzae

May 2008 , Volume 21 , Number  5
Pages  525 - 534

Junhyun Jeon,1 Jaeduk Goh,1 Sungyong Yoo,1 Myoung-Hwan Chi,1 Jaehyuk Choi,1 Hee-Sool Rho,1 Jongsun Park,1 Seong-Sook Han,2 Byeong Ryun Kim,2 Sook-Young Park,1 Soonok Kim,1 and Yong-Hwan Lee1

1Department of Agricultural Biotechnology, Center for Fungal Genetic Resources, Center for Agricultural Biomaterials, and Fungal Bioinformatics Lab, Seoul National University, Seoul 151-921, Korea; 2National Institute of Crop Science, Rural Development Administration, Suwon 441-857, Korea

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Accepted 19 January 2008.

Insertional mutagenesis of Magnaporthe oryzae led to the identification of MCK1, a pathogenicity gene predicted to encode mitogen-activated protein kinase kinase kinase (MAPKKK) homologous to BCK1 in Saccharomyces cerevisiae. Targeted disruption of MCK1 resulted in the fungus undergoing autolysis and showing hypersensitivity to cell-wall-degrading enzyme. The mck1 produced significantly reduced numbers of conidia and developed appressoria in a slightly retarded manner compared with the wild type. Appressorium of the mck1 mutant was unable to penetrate into plant tissues, thereby rendering the mutant nonpathogenic. Cytorrhysis assay and monitoring of lipid mobilization suggested that the appressorial wall was altered, presumably affecting the level of turgor pressure within appressorium. Furthermore, the mck1 mutant failed to grow inside plant tissue. Complementation of the mutated gene restored its ability to cause disease symptoms, demonstrating that MCK1 is required for fungal pathogenicity. Taken together, our results suggest that MCK1 is an MAPKKK involved in maintaining cell wall integrity of M. oryzae, and that remodeling of the cell wall in response to host environments is essential for fungal pathogenesis.

Additional keywords:Agrobacterium tumefaciens-mediated transformation (ATMT)

© 2008 The American Phytopathological Society