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分子植物育种,2007,第5 卷,第2 期,第23-24 页 Molecular Plant Breeding, 2007, Vol.5, No.2, 23-24 Genetic Analysis of Rice Mutants Identifies a New Locus at the Pi-ta Region Controlling Pathogen Recognition Y.L. Jia USDA-ARS Dale Bumpers National Rice Research Center, Stuttgart, AR, 72160, USA Corresponding email, [email protected] Understanding the molecular mechanisms of host and parasite interactions should facilitate the development of novel strategies to control plant diseases. Host interactions with biotrophic and hemi-biotrophic pathogens are known to follow a gene-for-gene specificity. The plant expresses a resistance (R) gene that is effective in preventing disease in response to pathogen races expressing the corresponding avirulence gene. We are studying the interaction mechanisms of the R gene, Pi-ta, in rice with the corresponding avirulence gene, AVR-Pita, found in the hemi-biotrophic pathogen, Magnaporthe oryzae (formerly Magnaporthe grisea). Pi-ta is a putative cytoplasmic receptor with a centrally localized nucleotide-binding site and leucine rich domain at the carboxyl terminus (Bryan et al., 2000; Jia et al., 2000). AVR-Pita is predicted to be a metalloprotease (Jia et al., 2006b). The putative processed protein, AVR-Pita176, has been shown to interact with the Pi-ta protein (Bryan et al., 2000; Jia et al., 2000).Additional evidence has been accumulated from other host and parasite systems to support the role of R genes in direct recognition of pathogen-signaling molecules in nature. Meanwhile, research in this area has also led to the development of both dominant and co-dominant markers from the Pi-ta gene (Jia et al., 2002; 2003; 2004). These user-friendly DNA markers have facilitated the identification and incorporation of the Pi-ta gene into elite germplasm worldwide (Wang et al., 2005; 2006). To facilitate the development of better molecular strategies to prevent blast disease, a genetic screening was performed to identify Pi-ta-mediated signaling components. A tropical japonica cultivar Katy from USA containing the Pi-ta gene introgressed from an indica cultivar Tetep was treated with 5 different doses of fast neutrons (Jia et al., 2006a). The screening of the blast susceptibility was performed in a greenhouse in 2003. The susceptible mutants have been advanced to M7, and confirmed to be derived from wild type Katy plants using 50 simple sequence repeat markers selected among 12 rice chromosomes. Putative mutations were identified at the Pi-ta locus and a novel nuclear gene Ptr(t) [Pi-ta required gene (temporary)]. Mutations in a line 2354 containing ptr(t) abolish the Pi-ta mediated resistance. Further genetic analysis revealed that the disruption of resistance is specific in the Pi-ta mediated signaling pathway. Ptr(t) is also tentatively mapped nearby the Pi-ta locus by analyzing a segregating population involving the crosses of 2354, and is being confirmed using additional mapping populations. Polymorphic SSRs at the Pi-ta region have been used to genotype recombinant lines of the crosses among mutants. The physical location of the Ptr(t) gene is further defined. Analysis of the candidate genes at the Pi-ta region is being performed, and progress will be presented. Keywords Oryza sativa L., Pi-ta resistance gene, Rice blast, Magnaporthe oryzae, NBS-LRD, Avirulence gene AVR-Pita Acknowledgements This work was mainly supported by USDA-ARS National Program NP301 genomic characterization of rice germplasm and the University of Arkansas (UA) Rice Research and Promotion Board. Cooperation and support of UA Rice Research and Extension Center, Plant Pathology, UA, Oakridge Laboratory, Zhejiang University, Zhejiang Wanli University, China Scholarship Research Council, South China Agricultural University, Kansas State References Bryan G.T., Wu K.S., Farrall L., Jia Y., Hershey H.P., McAdams S., Tarchini R., Donaldson G., Faulk K., and Valent B., 2000, A single amino acid difference distinguishes resistant and susceptible alleles of the rice blast resistance gene Pi-ta, Plant Cell, 12: 2033-2045 Jia Y., Bryan G.T., Farrall L., and Valent B., 2003, Natural variation at the Pi-ta rice blast resistance locus, Phytopathology, 93(11): 1452-1459 Jia Y., McAdams S.A., Bryan G.T., Hershey H.P., and Valent B., 2000, Direct interaction of resistance gene and avirulence gene products confers rice blast resistance, EMBO J., 19: 4004-4014 Jia Y., Redus M., Wang Z., and Rutger J.N., 2004, Development of a SNLP marker from the Pi-ta blast resistance gene by tri-primer PCR, Euphytica, 138: 97-105 Jia Y., Wang Z., and Singh P., 2002, Development of dominant rice blast resistance Pi-ta gene markers, Crop Sci., 42: 2145-2149 Jia Y., Xie J., and Rutger J.N., 2006a, Development and characterization of Katy deletion mutant populations for functional genomics of host-parasite interactions and rice improvement, Plant Mutation Reports, 1(1): 43-47 Jia Y., Zhou E., Winston E., Singh P., Correll J., Lee F.N., and Valent B., 2006b, Molecular co-evolution of the rice Pi-ta resistance gene and Magnaporthe oryzae avirulence gene AVR-Pita, In: Sanchez F., Quinto C., López-Lara I.M., and Geiger O. (eds.), Biology of plant-microbe interactions Vol. 5, The International Society for Molecular Plant-Microbe Interactions, St. Paul, USA, pp.325-331 Wang Z., Jia Y., Rutger J.N., and Xia Y., 2006, Rapid survey for presence of a blast resistance gene Pi-ta in rice cultivars using the dominant DNA markers derived from portions of the Pi-ta gene, Plant Breed., 126: 36-42 Wang Z., Redus M., and Jia Y., 2005, Establishment of codominant marker for rice blast resistance gene Pi-ta, Zhongguo Shuidao Kexue (Chinese Journal of Rice Science), 19(6): 483-488 (Chinese Journal in Chinese)