Abstract

The rice blast fungus Magnaporthe oryzae is a major threat to global rice production. To promote infection, the pathogen secretes effector proteins which manipulate host targets to promote virulence. Rice has evolved specific intracellular nucleotide-binding leucine rich repeat(NLR) proteins to activate plant defences in response to certain effectors. Recognition of one such effector, AVR -Pik, is mediated by the paired rice NLR proteins Pik-1/Pik-2. An integrated heavy metal associated (HMA) domain in Pik-1 binds to certain alleles of AVR -Pik to trigger disease resistance. Multiple Pik-1 alleles are present in rice, and exhibit differential responses to different AVR -Pik effector alleles. We have unpicked the molecular basis of how amino acid polymorphisms expand this differential response, and used natural variation to engineer expanded effector recognition capabilities to a Pik-1 allele. However, stealthy effector alleles AVR -PikC and AVR -PikF are not recognised by any Pik-1 alleles identified to date, thereby escaping plant defences. A family of small HMA domain-containing (sHMA) proteins have been identified as the host targets of AVR -Pik. We performed biochemical studies to show that AVR -PikC/AVR-PikF bind to sHMA1 in vitro. 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. In this presentation I will show our recent unpublished results demonstrating a novel approach to engineer improved NLRs capable of triggering immunity to previously unrecognised effectors.