Submitted to: International Congress on Molecular Plant-Microbe Interactions
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2005
Publication Date: 12/15/2005
Citation: Jia, Y., Zhou, E., Winston, E.M., Singh, P., Correll, J., Valent, B. 2005. Molecular co-evolution of the rice Pi-ta resistance gene and Magnaporthe grisea avirulence gene AVR-Pita [abstract]. International Congress on Molecular Plant-Microbe Interactions. p. 3-7. Available: http://www.lbt.unam.mx/Cancun2005/concurrent182.html.
Technical Abstract: Resistance to a biotrophic pathogen is often governed by a gene-for-gene relationship. A resistance (R) gene is effective in preventing infection by the pathogen containing the corresponding avirulence (AVR) gene. Molecular characterization of over 48 plant R genes has advanced the ability to breed for effective resistance against pathogens. Knowledge of DNA sequences of susceptible and resistant alleles not only enhances our understanding of R gene evolution, but can also be used to identify nucleotides that distinguish the resistant counterpart. These unique DNA sequences can be used to develop R gene specific primers to amplify portions of an R gene to use as a marker for marker-assisted selection (MAS). Blast disease is one of the most destructive rice diseases worldwide. The Pi-ta resistance gene is one of those R genes characterized at the molecular level. Pi-ta encodes a putative cytoplasmic protein with nucleotide binding sites and a leucine rich repeat. AVR-Pita encodes a metalloprotease, and its processed form AVR-Pita 176 interacts directly with the Pi-ta protein to trigger complete resistance to Magnaporthe grisea races containing the corresponding avirulence gene AVR-Pita. One resistant Pi-ta and three susceptible pi-ta alleles were identified from rice germplasm. An alignment of DNA sequences of these Pi-ta haplotypes identified several conserved nucleotide substitutions, and these nucleotide differences were used to develop PCR based markers for stacking the Pi-ta gene into advanced rice breeding lines by MAS. Similarly, results of structural and functional studies of avr-pita alleles in US M. grisea pathotypes suggest that transposition, insertion and deletion of DNA sequences at the AVR-Pita locus may be responsible for the instability of AVR-Pita, and thus it is a likely mechanism to defeat the resistance mediated by Pi-ta. Recent progress in understanding the coevolution of a plant R gene and a corresponding pathogen AVR gene and in developing the molecular methods for rice breeding and crop protection will be presented.