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Analysis of the Structure of the AVR1-CO39 Avirulence Locus in Virulent Rice-Infecting Isolates of Magnaporthe grisea

January 2002 , Volume 15 , Number  1
Pages  6 - 16

Mark L. Farman , 1 Yukiko Eto , 3 Tomomi Nakao , 3 Yukio Tosa , 3 Hitoshi Nakayashiki , 3 Shigeyuki Mayama , 3 and Sally A. Leong 1 , 2

1Department of Plant Pathology and 2USDA-ARS Plant Disease Resistance Research Unit, University of Wisconsin, Madison 53706, U.S.A.; 3Faculty of Agriculture, Kobe University, Nada, Kobe 657-8501, Japan

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Accepted 8 August 2001.

The AVR1-CO39 gene that came from a Magnaporthe grisea isolate from weeping lovegrass controls avirulence on the rice cultivar CO39. AVR1-CO39 was not present in the genome of the rice-infecting M. grisea isolate Guy11 from French Guyana, suggesting that the gene had been deleted. Molecular analysis of the deletion breakpoints in the AVR1-CO39 locus revealed the presence of a truncated copy of a previously unknown retrotransposon at the left-hand border. At the right-hand border was a truncated copy of another repetitive element that is present at multiple locations in the genome of Guy11. The structures of avr1-CO39 loci were further examined in 45 rice-infecting isolates collected in Brazil, China, Japan, India, Indonesia, Mali, and the Philippines. Most isolates showed no hybridization signal with the AVR1-CO39 probe and had the same locus structure as Guy11. Some isolates from Japan showed a signal with the AVR1-CO39 probe, but the region specifying avirulence activity was rearranged. These findings suggest that widespread virulence to ‘CO39’ among rice-infecting M. grisea isolates is due to ancestral rearrangements at the AVR1-CO39 locus that may have occurred early in the evolution of pathogenicity to rice.

The American Phytopathological Society, 2002