Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: February 29, 2004
Publication Date: February 1, 2005
Citation: Winston, E.M., Jia, Y., Correll, J. 2005. Molecular characterization of magnaporthe grisea avirulence alleles (avr-pita) in US pathotypes. Rice Technical Working Group Meeting Proceedings. Abstract p. 110. Technical Abstract: The rice blast fungus, Magnaporthe grisea Herbert (Barr), causes severe limitations in rice producing regions throughout the world. There are over 20 major genes for blast resistance (R) that have been identified in rice. Maintaining durable Pi-ta-mediated resistance is challenging due to the high degree of pathogenic variability and genetic instability of M. grisea avirulence alleles. Genetic mapping demonstrated that the M. grisea AVR-Pita gene is closely linked to the telometric region residing on chromosome 3. In addition, evidence suggests that races of the rice blast pathogen have the ability to mutate, thereby affecting host specificity. Isolates such as these are referred to as "race shift" isolates. The objective of this study was to determine the functionality of AVR-Pita alleles in isolates of M. grisea races found in the southern United States. Utilizing gene specific primers, the native promoter and coding regions of the AVR-Pita gene are being amplified from cDNA and genomic clones of the M. grisea wild-type isolates 0-137 and ZN61 (race IB-49), respectively. These fragments were directionally cloned into the fungal transformation vector pCB1004. Clones are being analyzed by ClaI and BamHI restriction digestion and PCR amplification using AVR-Pita gene specific primers. Clones exhibiting the predicted fragment size are being sequenced using the ABI-PRISM BigDyeTM Terminator cycle sequencing system. Positive clones will be homologous to AVR-Pita genomic sequence. Clones will be transformed into a race-shifted isolate to test the functionality of the AVR-Pita allele from ZN61. Complementation studies will be subsequently performed by inoculating the recombinant pathogen onto resistant rice cultivars, which contain Pi-ta to determine if the virulent isolate is converted to an avirulent isolate by the addition of AVR-Pita. These studies will provide direct evidence that AVR-Pita alleles can undergo spontaneous mutation and are deleted from the M. grisea genome. The data obtained from these experiments will enhance our knowledge in understanding the evolution of the rice blast fungus and the molecular mechanisms that are involved in Pi-ta-mediated resistance.