Leucine-rich repeats determine NLR helper-sensor specificity in a redundant immune signaling network
C. WU (1), A. Abd-El-Haliem (2), T. Bozkurt (3), K. Belhaj (4), J. Vossen (2), S. Kamoun (4) (1) The Sainsbury Laboratory, Norwich Research Park, United Kingdom; (2) Plant Breeding, Wageningen University, Netherlands; (3) Department of Life Sciences, Imperial College London, United Kingdom; (4) The Sainsbury Laboratory, Norwich Research Park, United Kingdom

Plants rely on nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins to respond to invading pathogens and activate immune responses. An emerging concept in NLR biology is that “sensor” NLR proteins are paired with “helper” NLR proteins to mediate immune signaling. However, our basic understanding in how sensor/helper NLR complexes mediate immunity remains limited. In this study, we discovered a complex NLR immune signaling network in which helper NLR in the NRC (NLR-required fro cell death) family are functionally redundant but display distinct specificities towards diverse sensor NLR. These sensor NLR form a phylogenetic superclade sister to the NRC clade, and altogether the NRC superclade forms ~1/3 of all NLR proteins in the Solanaceae. Although several sensor NLR, such as Rx, Bs2 and Sw5, signal via interchangeable NRC2, NRC3 or NRC4, some other sensor NLRs have a more limited downstream spectrum. For example, Prf signals via NRC2 or NRC3 but not NRC4, whereas Rpi-blb2 signals via NRC4. To determine the molecular basis of NRC helper specificity toward sensor NLR, we generated chimeric NRC3 and NRC4 constructs and investigated their specificities towards Prf and Rpi-blb2. Surprisingly, swapping the leucine-rich repeats (LRR) of NRCs resulted in chimeric proteins with altered spectrum of activity, indicating that the LRR region determines NLR helper-sensor specificity. These results provide new insights into sensor/helper NLR immune receptor complexes, by linking a large repertoire of NLR proteins into a complex immune signaling network. 

Abstract Number: P17-639
Session Type: Poster