An EDS1-SAG101 Complex Is Essential for TNL-Mediated Immunity in <i>Nicotiana benthamiana</i>

Abstract

Heterodimeric complexes containing the lipase-like protein ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) are regarded as central regulators of plant innate immunity. In this context, a complex of EDS1 with PHYTOALEXIN DEFICIENT4 (PAD4) is required for basal resistance and signaling downstream of immune receptors containing an N-terminal Toll-interleukin-1 receptor-like domain (TNLs) in Arabidopsis (<i>Arabidopsis thaliana</i>). Here we analyze EDS1 functions in the model Solanaceous plant <i>Nicotiana benthamiana</i> (<i>Nb</i>). Stable <i>Nb</i> mutants deficient in EDS1 complexes are not impaired in basal resistance, a finding which contradicts a general role for EDS1 in immunity. In <i>Nb</i>, PAD4 demonstrated no detectable immune functions, but TNL-mediated resistance responses required EDS1 complexes incorporating a SENESCENCE ASSOCIATED GENE101 (SAG101) isoform. Intriguingly, <i>SAG101</i> is restricted to those genomes also encoding TNL receptors, and we propose it may be required for TNL-mediated immune signaling in most plants, except the Brassicaceae. Transient complementation in <i>Nb</i> was used for accelerated mutational analyses while avoiding complex biotic interactions. We identify a large surface essential for EDS1-SAG101 immune functions that extends from the N-terminal lipase domains to the C-terminal EDS1-PAD4 domains and might mediate interaction partner recruitment. Furthermore, this work demonstrates the value of genetic resources in <i>Nb</i>, which will facilitate elucidation of EDS1 functions.