AtCDC48A is involved in the turnover of an NLR immune receptor

Plants rely on different immune receptors to recognize pathogens and defend against pathogen attacks. Nucleotide-binding domain and leucine-rich repeat (NLR) proteins play a major role as intracellular immune receptors. Their homeostasis must be maintained at optimal levels in order to effectively recognize pathogens without causing autoimmunity. Previous studies have shown that the activity of the ubiquitin-proteasome system is essential to prevent excessive accumulation of NLR proteins such as Suppressor of NPR1, Constitutive 1 (SNC1). Attenuation of the ubiquitin E3 ligase SCFCPR1 (Constitutive expressor of Pathogenesis Related genes 1) or the E4 protein MUSE3 (Mutant, SNC1-Enhancing 3) leads to NLR accumulation and autoimmunity. In the current study, we report the identification of AtCDC48A as a negative regulator of NLR-mediated immunity. Plants carrying Atcdc48A-4, a partial loss-of-function allele of AtCDC48A, exhibit dwarf morphology and enhanced disease resistance to the oomycete pathogen Hyaloperonospora arabidopsidis (H.a.) Noco2. The SNC1 level is increased in Atcdc48A-4 plants and AtCDC48A interacts with MUSE3 in co-immunoprecipitation experiments, supporting a role for AtCDC48A in NLR turnover. While Arabidopsis contains four other paralogs of AtCDC48A, knockout mutants of these genes do not show obvious immunity-related phenotypes, suggesting functional divergence within this family. As an AAA-ATPase, AtCDC48A likely serves to process the poly-ubiquitinated NLR substrate for final protein degradation by the 26S proteasome.