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United States Department of Agriculture

Agricultural Research Service

Title: Instability of the Magnaporthe oryzae Avirulence gene AVR-Pita alters virulence

Authors
item Zhou, Erxun - SOUTH CHINA AGRIC. UNIV.
item Jia, Yulin
item Singh, Pratibha - CORNELL UNIV.
item Correll, James - UNIV. OF AR
item Lee, Fleet - UNIV. OF AR RREC

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 10, 2007
Publication Date: February 21, 2007
Citation: Zhou, E., Jia, Y., Singh, P., Correll, J.C., Lee, F.N. 2007. Instability of the Magnaporthe oryzae Avirulence gene AVR-Pita alters virulence. Fungal Genetics and Biology. 44:1024-1034.

Interpretive Summary: Blast disease caused by the fungal pathogen Magnaporthe oryzae is the most damaging disease of rice. Thirty major resistance genes have been used in classical plant breeding for developing improved resistance. However, any resistance based on a single major resistance gene has often been defeated by the pathogen, and resistance can last for a few years after its deployment. This study addresses the molecular mechanism of instability of blast resistance using a matched paired resistance gene Pi-ta and the avirulence gene AVR-Pita. AVR-Pita triggers effective resistance mediated by Pi-ta in rice. We analyzed the structures of the AVR-Pita allele in 39 U.S. isolates of M. oryzae using a series of allele-specific primers. The highly homologous alleles of the AVR-Pita gene were amplified from all avirulent isolates. Sequence analysis of five avirulent 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 allele were not detected in the most virulent isolates, and significant variation 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. Thus it is important to stack.

Technical Abstract: 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.

Last Modified: 10/20/2014
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