Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2001
Publication Date: 1/1/2002
Citation: FARMAN, M.L., ETO, Y., NAKAO, T., TOSA, Y., NAKAYASHIKI, H., MAYAMA, S., LEONG, S.A. ANALYSIS OF THE STRUCTURE OF THE AVR1-CO39 AVIRULENCE LOCUS IN VIRULENT RICE-INFECTING ISOLATES OF MAGNAPORTHE GRISEA. MOLECULAR PLANT-MICROBE INTERACTIONS. 2002. 15:6-16. Interpretive Summary: Rice blast disease is the most important fungal disease of rice worldwide. Genetic resistance continues to be the most sustainable and economically viable method of disease control throughout the world. However, newly deployed genes that give rise to genetic resistance to this disease in rice are rapidly overcome by the pathogen. The molecular basis of this ability to increase in virulence by the fungus is poorly understood. We describe here several kinds of mutational events that have taken place in a fungal gene whose product is detected by rice plants carrying a specific disease resistance gene. These mutations give rise to fungal isolates that are highly virulent on rice plants with this resistance gene and provide a molecular explanation for the increased virulence of these isolates on this rice germplasm. This work will be of interest to plant breeders and molecular biologists who seek to enhance the resistance of rice cultivars to this fungus and to detect fungal lines that may have enhanced pathogenicity on rice.
Technical Abstract: The AVR1-CO39 gene which is present in 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, 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 element that is present at multiple locations i the genome of Guy11. The structures of AVR1-CO39 loci were further examined in 35 rice-infecting isolates collected in Brazil, China, Japan, and Indonesia. Most isolates showed no hybridization signal with the AVR1-CO39 probe, and had the same locus structure as Guy11. Some Japanese isolates showed a signal with the AVR1-CO39 probe, but their AVR1-CO39 locus showed other type of rearrangements. These findings suggest that broad virulence to CO39 among rice-infecting M. grisea isolates is due to ancestral rearrangements at the AVR1-CO39 locus, which may have occurred early in the evolution of pathogenicity to rice.