Instability of the Magnaporthe oryzae avirulence gene AVR-Pita alters virulence
Zhou, E.X. | Jia, Y.L. | Singh, P. | Correll, J.C. | Lee, F.N.
Fungal genetics and biology : FG & BVolume 44 ISSN 1087-1845
Dna primers; Avirulence genes; Nucleotide sequences; Plant pathogenic fungi; Magnaporthe oryzae; Blast disease; Avr-pita gene
The avirulence gene AVR-Pita of Magnaporthe oryzae determines the efficacy of the resistance gene Pi-ta in rice. The structures of the AVR-Pita alleles in 39 US isolates of M. oryzae were analyzed using polymerase chain reaction. A series of allele-specific primers were developed from the AVR-Pita gene to examine the presence of AVR-Pita. Orthologous alleles of the AVR-Pita gene were amplified from avirulent isolates. Sequence analysis of five alleles revealed three introns at identical positions in the AVR-Pita gene. All five alleles were predicted to encode metalloprotease proteins highly similar to the AVR-Pita protein. In contrast, the same regions of the AVR-Pita alleles were not amplified in the most virulent isolates, and significant variations of DNA sequence at the AVR-Pita allele were verified by Southern blot analysis. A Pot3 transposon was identified in the DNA region encoding the putative protease motif of the AVR-Pita protein from a field isolate B2 collected from a Pi-ta-containing cultivar Banks. These findings show that transposons can contribute to instability of AVR-Pita and is one molecular mechanism for defeating resistance genes in rice cultivar Banks. Includes references
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