Chromosome Walking to the AVR1-CO39 Avirulence Gene of Magnaporthe grisea: Discrepancy Between the Physical and Genetic Maps

Corresponding author: Sally A. Leong, Department of Plant Pathology and USDA-ARS Plant Disease Resistance Research Unit, University of Wisconsin, Madison, WI 53706., sal{at}plantpath.wisc.edu (E-mail).

Communicating editor: P. J. PUKKILA

The avrCO39 gene conferring avirulence toward rice cultivar CO39 was previously mapped to chromosome 1 of Magnaporthe grisea between cosegregating markers CH5-120H and 1.2H and marker 5-10-F. In the present study, this region of the chromosome was physically mapped using RecA-mediated Achilles' cleavage. Cleavage of genomic DNA sequences within CH5-120H and 5-10-F liberated a 610-kb restriction fragment, representing the physical distance between these markers. Chromosome walking was initiated from both markers but was curtailed due to the presence of repetitive DNA sequences and the absence of overlapping clones in cosmid libraries representing several genome equivalents. These obstacles were overcome by directly subcloning the target region after release by Achilles' cleavage and a contig spanning avrCO39 was thus assembled. Transformation of two cosmids into a virulent recipient strain conferred a cultivar-specific avirulence phenotype thus confirming the cloning of avrCO39. Meiotic crossover points were unevenly distributed across this chromosomal region and were clustered around the avrCO39 locus. A 14-fold variation in the relationship between genetic and physical distance was measured over the avrCO39 chromosomal region. Thus the poor correlation of physical to genetic distance previously observed in M. grisea appears to be manifested over relatively short distances.

This article has been cited by other articles:

				B. C. Couch, I. Fudal, M.-H. Lebrun, D. Tharreau, B. Valent, P. van Kim, J.-L. Notteghem, and L. M. Kohn Origins of Host-Specific Populations of the Blast Pathogen Magnaporthe oryzae in Crop Domestication With Subsequent Expansion of Pandemic Clones on Rice and Weeds of Rice Genetics, June 1, 2005; 170(2): 613 - 630. [Abstract] [Full Text] [PDF]

				H. U. Bohnert, I. Fudal, W. Dioh, D. Tharreau, J.-L. Notteghem, and M.-H. Lebrun A Putative Polyketide Synthase/Peptide Synthetase from Magnaporthe grisea Signals Pathogen Attack to Resistant Rice PLANT CELL, September 1, 2004; 16(9): 2499 - 2513. [Abstract] [Full Text] [PDF]

				R. Linning, D. Lin, N. Lee, M. Abdennadher, D. Gaudet, P. Thomas, D. Mills, J. W. Kronstad, and G. Bakkeren Marker-Based Cloning of the Region Containing the UhAvr1 Avirulence Gene From the Basidiomycete Barley Pathogen Ustilago hordei Genetics, January 1, 2004; 166(1): 99 - 111. [Abstract] [Full Text] [PDF]

				W. Gao, C. H. Khang, S.-Y. Park, Y.-H. Lee, and S. Kang Evolution and Organization of a Highly Dynamic, Subtelomeric Helicase Gene Family in the Rice Blast Fungus Magnaporthe grisea Genetics, September 1, 2002; 162(1): 103 - 112. [Abstract] [Full Text] [PDF]

				M. L. Farman Meiotic Deletion at the BUF1 Locus of the Fungus Magnaporthe grisea Is Controlled by Interaction With the Homologous Chromosome Genetics, January 1, 2002; 160(1): 137 - 148. [Abstract] [Full Text] [PDF]

				M. J. Orbach, L. Farrall, J. A. Sweigard, F. G. Chumley, and B. Valent A Telomeric Avirulence Gene Determines Efficacy for the Rice Blast Resistance Gene Pi-ta PLANT CELL, November 1, 2000; 12(11): 2019 - 2032. [Abstract] [Full Text]