22Plant NLR receptors detect pathogen effectors and initiate an immune response. Since 23 their discovery, NLRs have been the focus of protein engineering to improve disease 24 resistance. However, this has proven challenging, in part due to their narrow response 25 specificity. Here, we used structure-guided engineering to expand the response 26 profile of the rice NLR Pikp to variants of the rice blast pathogen effector AVR-Pik. A 27 mutation located within an effector binding interface of the integrated Pikp-HMA 28 domain increased the binding affinity for AVR-Pik variants in vitro and in vivo. This 29 translates to an expanded cell death response to AVR-Pik variants previously 30 unrecognized by Pikp in planta. Structures of the engineered Pikp-HMA in complex 31 with AVR-Pik variants revealed the mechanism of expanded recognition. These 32 results provide a proof-of-concept that protein engineering can improve the utility of 33 plant NLR receptors where direct interaction between effectors and NLRs is 34 established, particularly via integrated domains. 35 36Protein engineering offers opportunities to develop new or improved molecular 37 recognition capabilities that have applications in basic research, health and 38 agricultural settings. Protein resurfacing, where the properties of solvent-exposed 39 regions are changed (often by mutation), has been used extensively in diverse areas 40 from antibody engineering for clinical use, to production of more stable, soluble 41 proteins for biotechnology applications (1). 42