The isolation and characterization of Pik, a rice blast resistance gene which emerged after rice domestication

P>The rice-rice blast pathosystem is of great interest, not only because of the damaging potential of rice blast to the rice crop, but also because both the pathogen and its host are experimentally amenable. The rice blast resistance gene Pik, which is one of the five classical alleles located at the Pik locus on the long arm of chromosome 11, confers high and stable resistance to many Chinese rice blast isolates. The isolation and functional characterization of Pik were performed in the present study through genetic and genomic approaches. A combination of Pik-1 and Pik-2 is required for the expression of Pik resistance. Both Pik-1 and Pik-2 encode coiled-coil nucleotide binding site leucine-rich repeat (NBS-LRR) proteins, and each shares a very high level of protein identity with corresponding proteins encoded by the Pik-m and Pik-p alleles. Pik could be distinguished from other Pik alleles, including Pik-m and Pik-p, by the allele-specific, single-nucleotide polymorphism T1-2944G. The coupled genes probably did not evolve as a result of a duplication event, and are far from any NBS-LRR R gene characterized. Pik is a younger allele at the locus that probably emerged after rice domestication.