PT - JOURNAL ARTICLE AU - Danalyn R. Holmes AU - Melissa Bredow AU - Kathrin Thor AU - Sydney A. Pascetta AU - Irina Sementchoukova AU - Kristen R. Siegel AU - Cyril Zipfel AU - Jacqueline Monaghan TI - A novel allele in the <em>Arabidopsis thaliana</em> MACPF protein CAD1 results in deregulated immune signaling AID - 10.1101/2021.01.28.428637 DP - 2021 Jan 01 TA - bioRxiv PG - 2021.01.28.428637 4099 - http://biorxiv.org/content/early/2021/01/28/2021.01.28.428637.short 4100 - http://biorxiv.org/content/early/2021/01/28/2021.01.28.428637.full AB - Immune recognition in plants is governed by two major classes of receptors: pattern recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat receptors (NLRs). Located at the cell surface, PRRs bind extracellular ligands originating from microbes (indicative of ‘non-self’) or damaged plant cells (indicative of ‘infected-self’), and trigger signaling cascades to protect against infection. Located intracellularly, NLRs sense pathogen-induced physiological changes and trigger localized cell death and systemic resistance. Immune responses are under tight regulation in order to maintain homeostasis and promote plant health. In a forward-genetic screen to identify regulators of PRR-mediated immune signaling, we identified a novel allele of the membrane-attack complex and perforin (MACPF)-motif containing protein CONSTITUTIVE ACTIVE DEFENSE 1 (CAD1) resulting from a missense mutation in a conserved N-terminal cysteine. We show that cad1-5 mutants display deregulated immune signaling and symptoms of autoimmunity dependent on the lipase-like protein ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), suggesting that CAD1 integrity is monitored by the plant immune system. We further demonstrate that CAD1 localizes to both the cytosol and plasma membrane using confocal microscopy and subcellular fractionation. Our results offer new insights into immune homeostasis and provide tools to further decipher the intriguing role of MACPF proteins in plants.Competing Interest StatementThe authors have declared no competing interest.