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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
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