Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: 5/14/2012
Publication Date: 8/4/2012
Citation: Jia, Y., Zhang, Z., Xing, J., Wang, J., Correll, J.C., Cartwright, R. 2012. Natural Variation and Evolution of the Avirulence Genes in Magnaporthe Oryzae. American Phytopathological Society. published online. Interpretive Summary:
Technical Abstract: The avirulence genes in Magnaporthe oryzae are important determinants for the corresponding resistance genes in rice. In the present study, we analyzed DNA sequence variation of the five avirulence genes, AVR-Pita1, AVR-Pik, AVR-Piz(t), AVR-Pia and AVR-Pii in field blast isolates in order to understand the effectiveness of the resistance genes, Pi-ta, Pi-k, Pi-z, Pi-a and Pi-i. Genomic DNA of 350 blast isolates collected from the southern US from 1970-2009 were used for PCR amplification to examine the existence of AVR-Pita1, AVR-Pik, AVR-Piz(t) and AVR-Pia using gene specific PCR markers. Results of PCR products revealed that 230 isolates of M. oryzae carry AVR-Pita1, 200 isolates carry AVR-Piz(t), 40 isolates carry AVR-Pik, 10 isolates carry AVR-Pia, and 1 isolates carries AVR-Pii. PCR products were sequenced, and DNA sequence variation was analyzed by DNAsp 4.5 and TCS1.21. It was found that AVR-Pita1 was highly unstable, and a total of 40 AVR-Pita1 variants were identified in avirulent isolates whereas another 4 AVR genes were relatively stable with few minor sequence changes. Point mutation, insertion, deletion of nucleotides, and transposon insertions resulting in altered AVR proteins were found in virulent isolates. These findings suggest that M. oryzae utilizes a sophisticated and multifaceted mechanism to “defeat” host resistance genes. The impact of these findings for breeding for improved blast resistance using major resistance genes will be presented.