背景回顾：Throughout their evolution, plant nucleotide-binding leucine-rich-repeat receptors (NLRs) have acquired widely divergent unconventional integrated domains that enhance their ability to detect pathogen effectors. 

提出问题：However, the functional dynamics that drive the evolution of NLRs with integrated domains (NLR-IDs) remain poorly understood. 

主要发现：Here, we reconstructed the evolutionary history of an NLR locus prone to unconventional domain integration and experimentally tested hypotheses about the evolution of NLR-IDs. 

结果1-Pias-1/Pias-2：We show that the rice (Oryza sativa) NLR Pias recognizes the effector AVR-Pias of the blast fungal pathogen Magnaporthe oryzae. Pias consists of a functionally specialized NLR pair, the helper Pias-1 and the sensor Pias-2, that is allelic to the previously characterized Pia pair of NLRs: the helper RGA4 and the sensor RGA5.  

结果2-Pias-2：Remarkably, Pias-2 carries a C-terminal DUF761 domain at a similar position to the heavy metal–associated (HMA) domain of RGA5. Phylogenomic analysis showed that Pias-2/RGA5 sensor NLRs have undergone recurrent genomic recombination within the genus Oryza, resulting in up to six sequence-divergent domain integrations. Allelic NLRs with divergent functions have been maintained transspecies in different Oryza lineages to detect sequence-divergent pathogen effectors. 

结果3-Pias-1：By contrast, Pias-1 has retained its NLR helper activity throughout evolution and is capable of functioning together with the divergent sensor-NLR RGA5 to respond to AVR-Pia. 

结论：These results suggest that opposite selective forces have driven the evolution of paired NLRs: highly dynamic domain integration events maintained by balancing selection for sensor NLRs, in sharp contrast to purifying selection and functional conservation of immune signaling for helper NLRs.

 摘 要 

在植物核苷酸结合、富含亮氨酸重复受体NLRs的演化过程中，其获得了很多不同的、新的集成结构域，能够增强其检测病原菌效应物的能力。但是，驱动带有集成结构域的NLRs（NLR-IDs）的功能动态演化仍不清楚。本文中，作者重建了一个易于整合新结构域的NLR位点的演化历史，并且通过实验测试了关于NLR-IDs的假说。作者发现水稻的NLR Pias能够识别稻瘟病菌Magnaporthe oryzae的效应子AVR-Pias。Pias包含一个功能特化的NLR对，包含一个helper NLR Pias-1和一个sensor NLR Pias-2，这一对是之前鉴定到的NLR Pia对helper RGA4和sensor RGA5的等位基因。有趣的是，Pias-2包含一个C端DUF761结构域，与RGA5上重金属相关结构域HMA的位置差不多。系统发育基因组学分析显示，Pias-2/RGA5 sensor NLRs在稻属植物中经历了反复的基因组重组，导致了最多达6个序列明显分化的结构域整合。具有功能分化的NLRs等位基因在不同的稻属谱系之间跨种保存，以检测序列分歧严重的病原物效应子。相反，Pias-1在演化过程中保留了其NLR helper活性，并且能够与分化的sensor-NLR RGA5一起发挥作用，以响应AVR-Pia。本文的研究结果揭示了相反的选择压驱动了成对NLRs的演化：对于sensor NLRs来说，通过平衡选择维持了高度波动的结构域整合事件；这与helper NLRs上发生的纯化选择及在免疫信号转导中保守功能形成鲜明对比。