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Crystals to crops: using host targets of a rice blast pathogen effector protein to engineer a plant immune receptor with novel recognition specificity

Josephine Maidment: John Innes Centre

<div><em>Magnaporthe oryzae</em> causes rice blast disease and is a major threat to global food security. During infection, this pathogen secretes effector proteins which manipulate host targets to promote virulence. Some effectors are recognised by specific nucleotide-binding leucine rich repeat (NLR) proteins in rice to trigger plant defences. Recognition of the effector AVR-Pik is mediated by the paired rice NLRs Pik-1/Pik-2. An integrated heavy metal associated (HMA) domain was previously identified in Pik-1, to which certain alleles of AVR-Pik directly bind to trigger disease resistance. Multiple alleles of Pik-1 have evolved in rice and display differential responses to different AVR-Pik effectors. However, the stealthy effector alleles AVR-PikC/AVR-PikF do not interact with any Pik-1 alleles, evading plant defences. A family of small HMA domain-containing (sHMA) proteins have been identified as the host targets of AVR-Pik. Analytical gel filtration revealed that AVR-PikC/AVR-PikF bind to sHMA1 <em>in vitro</em>. We hypothesised that modifying the HMA domain of Pikp-1 to resemble sHMA1 would extend the response of the NLR to AVR-PikC/AVR-PikF. To guide engineering, we solved the crystal structure of AVR-PikF in complex with sHMA1. Using this, we produced a novel NLR which triggered an immune response to AVR-PikC in <em>Nicotiana benthamiana. </em>This study reveals a novel approach to engineer improved NLR proteins capable of triggering immunity to previously unrecognised effectors.</div>