NRG1 is required for the function of the TIR-NLR immune receptors Roq1 and RPP1 in Nicotiana benthamiana

Abstract

The plant immune system involves a large family of nucleotide-binding leucine-rich repeat (NLR) intracellular immune receptors. These immune receptors often function to directly or indirectly mediate the perception of specific pathogen effector proteins secreted into the cell. Activation of these immune receptors typically results in activation of the immune system and subsequent suppression of pathogen proliferation. Although many examples of NLR receptors are known, a mechanistic understanding of how receptor activation ultimately leads to an immune response is not well understood. A subset of the NLR proteins contain a TIR domain at their N terminus (TNL). One such TNL, the N gene, was previously shown to depend on a non-TIR NLR protein, N requirement gene 1 (NRG1) for immune function. We tested additional NLR proteins in Nicotiana benthamiana for dependency on NRG1. We found that two additional TIR-NLR proteins, Roq1 and RPP1, also require NRG1 but that two coiled-coil NLR proteins, Bs2 and Rps2, do not. This finding suggests that NRG1 may be a conserved component of TNL signaling pathways.