A Coevolved EDS1-SAG101-NRG1 Module Mediates Cell Death Signaling by TIR-Domain Immune Receptors.

Plant nucleotide binding/leucine-rich repeat (NLR) immune receptors are activated by pathogen effectors to trigger host defenses and cell death. Toll-interleukin 1 receptor domain NLRs (TNLs) converge on the ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) family of lipase-like proteins for all resistance outputs. In Arabidopsis () TNL-mediated immunity, EDS1 heterodimers with PHYTOALEXIN DEFICIENT4 (PAD4) transcriptionally induced basal defenses. EDS1 uses the same surface to interact with PAD4-related SENESCENCE-ASSOCIATED GENE101 (SAG101), but the role of EDS1-SAG101 heterodimers remains unclear. We show that EDS1-SAG101 functions together with N REQUIRED GENE1 (NRG1) coiled-coil domain helper NLRs as a coevolved TNL cell death-signaling module. EDS1-SAG101-NRG1 cell death activity is transferable to the Solanaceous species and cannot be substituted by EDS1-PAD4 with NRG1 or EDS1-SAG101 with endogenous NRG1. Analysis of EDS1-family evolutionary rate variation and heterodimer structure-guided phenotyping of EDS1 variants and PAD4-SAG101 chimeras identify closely aligned ɑ-helical coil surfaces in the EDS1-SAG101 partner C-terminal domains that are necessary for reconstituted TNL cell death signaling. Our data suggest that TNL-triggered cell death and pathogen growth restriction are determined by distinctive features of EDS1-SAG101 and EDS1-PAD4 complexes and that these signaling machineries coevolved with other components within plant species or clades to regulate downstream pathways in TNL immunity.