Structure-guided engineering of synthetic immune receptors against the blast fungus
Plant pathogens secrete a plethora of effector proteins to enable colonization of their hosts. These effectors interact with intracellular plant proteins to alter their function and promote infection. Plants are generally effective at fighting off pathogens and have evolved an effective immune system, including immune receptors of the nucleotide-binding, leucine-rich repeat proteins (NLR) class. However, NLRs tend to have a narrow recognition spectrum limiting their value in modern agriculture. Here, we present a strategy to improve NLR-mediated plant immunity using structural information of effector-target complexes. The fungus Magnaporthe oryzae (syn. Pyricularia oryzae) is one of the most devastating plant pathogens causing blast disease on a wide range of monocot hosts, including rice, wheat, and millet. The M. oryzae effector AVR-Pik is recognized by the rice NLR pair Pik1/2 through binding to a heavy metal associated (HMA) domain that has integrated into Pik-1. We identified a sequence related effector, APikL2 (AVR-Pik like 2), which is conserved in nearly all M. oryzae isolates. Similar to AVR-Pik, APikL2 binds to HMA containing proteins and structural analyses revealed a common HMA-binding interface between these two effectors. However, APikL2 is not recognized by the NLR pair Pik1/2 and because it is widespread in M. oryzae is a high value target for blast disease resistance development. We combined sequence alignments and structure-based information derived from effector-target complexes to identify polymorphic residues around the effector-HMA binding interface that could define binding specificity of the NLR. We then introduced these residues into the HMA-domain of the Pik1 NLR to generate synthetic immune receptors that bind APikL2 and thus carry expanded effector binding spectra. Our work highlights how basic understanding of the biochemical and biophysical basis of pathogen-host interactions can be used to retool plant immunity and generate novel immune receptor functionalities.