Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2001
Publication Date: 1/31/2002
Citation: Farman, M.L., Eto, Y., Tosa, Y., Nakayashiki, H., Mayama, S., Leong, S.A. 2002. Analysis of the Structure of the AVR1-CO39 Avirulence Locus in Virulent Rice-Infecting Isolates of Magnaporthe grisea. Molecular Plant-Microbe Interactions. 15:6-16. Interpretive Summary: Rice plants recognize the rice blast fungus through sensing of fungal avirulence gene products. Our work has led to the isolatino of the fungal avirulence gene AVR1-CO39, which causes a resistance response in rice varieties carrying the corresponding rice resistance locus. This study examined the structure of this fungal gene in many rice-infecting isolates of the rice blast fungus and revealed that the gene is mutated in most isolates. These mutations allow these strains of the fungus to be virulent on rice varieties carrying the corresponding rice resistance locus and provides new insight on how fungal avirulence genes mutant to allow the pathogen to become more virulent on rice.
Technical Abstract: 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 lefthand 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.