Plant major resistance (R) genes are effective in detecting pathogen signal molecules and triggering robust defense responses. Investigating the natural variation in R genes will allow identification of the critical amino acid residues determining recognition specificity in R protein and the discovery of novel R alleles. The rice blast resistance gene Pike, comprising of two adjacent CC-NBS-LRR genes, namely, Pike-1 and Pike-2, confers broad-spectrum resistance to Magnaporthe oryzae. Here, we demonstrated that Pike-1 determined Pike-specific resistance through direct interaction with the pathogen signal molecule AvrPik. Analysis of natural variation in 79 Pike-1 variants in the Asian cultivated rice Oryza sativa and its wild relatives revealed that the CC and NBS regions, particularly the CC region of the Pike-1 protein were the most diversified. We also found that balancing selection had occurred in O. sativa and O. rufipogon to maintain the genetic diversity of the Pike-1 alleles. By analysis of amino acid sequences, we identified 40 Pike-1 variants in these rice germplasms. These variants were divided into three major groups that corresponded to their respective clades. A new Pike allele, designated Pikg, that differed from Pike by a single amino acid substitution (D229E) in the Pike-1 CC region of the Pike protein was identified from wild rice relatives. Pathogen assays of Pikg transgenic plants revealed a unique reaction pattern that was different from that of the previously identified Pike alleles, namely, Pik, Pikh, Pikm, Pikp, Piks and Pi1. These findings suggest that minor amino acid residues in Pike-1/Pikg-1 determine pathogen recognition specificity and plant resistance. As a new blast R gene derived from rice wild relatives, Pikg has potential applications in rice breeding.

植物主要抗性（R）基因可有效检测病原体信号分子并触发强大的防御反应。研究R基因的自然变异将允许鉴定关键氨基酸残基，从而确定R蛋白的识别特异性并发现新的R等位基因。稻瘟病抗性基因Pike由两个相邻的CC-NBS-LRR基因组成，即Pike-1和Pike-2，赋予水稻对稻瘟病菌的广谱抗性。在这里，我们证明了派克1决定了派克通过与病原体信号分子AvrPik的直接相互作用实现特异性耐药。对亚洲栽培水稻稻及其野生近缘种中79个Pike-1变异体的自然变异进行分析后发现，Pike-1蛋白的CC和NBS区域，尤其是CC区域最为多样化。我们还发现，在O. sativa和O. rufipogon中发生了平衡选择，以维持Pike-1等位基因的遗传多样性。通过氨基酸序列分析，我们在这些水稻种质中鉴定出40个Pike-1变异体。这些变体分为对应于其各自进化枝的三个主要组。新的派克等位基因，已指定从野生稻亲缘中鉴定出与Pike不同的Pikg，其在Pike蛋白的Pike-1 CC区域具有单个氨基酸取代（D229E）。Pikg转基因植物的病原体测定揭示了一种独特的反应模式，该模式不同于先前鉴定的Pike等位基因，即Pik，Pikh，Pikm，Pikp，Piks和Pi1。这些发现表明，Pike-1 / Pikg-1中的次要氨基酸残基决定了病原体的识别特异性和植物抗性。作为水稻野生近缘种Pikg的新blast R基因 在水稻育种中具有潜在的应用。