Allelic variants of the NLR protein Rpi-chc1 differentially recognise members of the Phytophthora infestans PexRD12/31 effector superfamily through the leucine-rich repeat domain

O_LIPhytophthora infestans is a pathogenic oomycete that causes the infamous potato late blight disease. Resistance (R) genes from diverse Solanum species encode intracellular receptors that recognize P. infestans RXLR effector proteins and provide effective defence responses. To deploy these R genes in a durable fashion in agriculture, we need to understand the mechanism of effector recognition and the way the pathogen evades recognition. C_LIO_LIWe cloned sixteen allelic variants of the Rpi-chc1 gene from Solanum chacoense and other Solanum species, and identified the cognate P. infestans RXLR effectors. These tools were used to study receptor-ligand interactions and co-evolution. C_LIO_LIFunctional and non-functional alleles of Rpi-chc1 encode Coiled-Coil-Nucleotide Binding-Leucine-Rich-Repeat (CNL) proteins. Rpi-chc1.1 recognised multiple PexRD12 (AVRchc1.1) proteins while Rpi-chc1.2 recognised multiple PexRD31 (AVRchc1.2) proteins, both from the PexRD12/31 superfamily. Domain swaps between Rpi-chc1.1 and Rpi-chc1.2 revealed that overlapping subdomains in the LRR were responsible for the difference in effector recognition. C_LIO_LIThis study showed that Rpi-chc1.1 and Rpi-chc1.2, evolved to recognize distinct members of the same PexRD12/31 effector family via the LRR domain. The biased distribution of polymorphisms suggests that exchange of LRRs during host-pathogen co-evolution can lead to novel recognition specificities. These insights will help future strategies to breed for durable resistant varieties. C_LI