Canonical NLR immune receptor architecture enforces EDS1-dependency onto divergent TIR domains

Toll/interleukin-1 receptor (TIR) enzymes are prominent immune components in diverse organisms across the tree of life. In flowering plants, TIRs are often integrated into nucleotide binding leucine-rich repeat (NLR) receptors whose oligomerization-dependent biochemical activities create second messengers perceived by ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1)-family signaling complexes. TIR-NLRs and TIR proteins are present across the full spectrum of plant evolution, yet EDS1 signaling is a derived trait in seed plants. Here, we examined the functional dependency of diverse plant TIRs on the EDS1 pathway in the angiosperms Nicotiana benthamiana and Nicotiana tabacum . While the isolated TIR domains from non-seed plants generally required EDS1 for immune cell death activation, we also identified TIRs that functioned independent of EDS1. However, chimeric TIR-NLRs incorporating these diverse TIR domains onto the AtWRR4a receptor chassis showed a full reversion to EDS1-dependency. Extending this phenomenon further, we demonstrated that the AtWRR4a architecture enforces EDS1-dependence onto a bacterial TIR domain that is otherwise EDS1-independent. Collectively, our work demonstrates that NLR immune receptor architecture influences TIR-related immunity and provides further context to their ancient acquisition into plant immune systems.