EDS1 signalling: At the nexus of intracellular and surface receptor immunity.

The conserved lipase-like protein EDS1 transduces signals from pathogen-activated intracellular nucleotide-binding leucine-rich repeat (NLR) receptors to transcriptional defences and host cell death. In this pivotal NLR signalling role, EDS1 works as a heterodimer with each of its partners, SAG101 and PAD4. Different properties of EDS1-SAG101 and EDS1-PAD4 complexes and functional relationships to sensor and helper NLRs have emerged. EDS1-SAG101 dimers confer effector-triggered immunity mediated by intracellular TNL receptors. In contrast, EDS1-PAD4 dimers have a broader role promoting basal immune responses that can be initiated inside cells by TNL- or CNL-type NLRs, and at the cell surface by LRR-receptor proteins. Characterizing the essential elements of these two EDS1 modules will help to connect intracellular and surface receptor signalling networks in the plant immune system.