Plant mixed lineage kinase domain-like proteins limit biotrophic pathogen growth

Abstract

AbstractMixed lineage kinase domain-like (MLKL) protein mediates necroptotic cell death in vertebrates. We report here the discovery of a conserved protein family across seed plants that is structurally homologous to vertebrate MLKL. TheArabidopsis thalianagenome encodes three MLKLs with overlapping functions in limiting growth of obligate biotrophic fungal and oomycete pathogens. Although displaying a cell death activity mediated by N-terminal helical bundles, termed HeLo domain,AtMLKL-dependent immunity can be separated from host cell death. Cryo-electron microscopy structures ofAtMLKLs reveal a tetrameric configuration, in which the pseudokinase domain and brace region bury the HeLo-domains, indicative of an auto-repressed complex. We also show the association of twoAtMLKLs with microtubules. These findings, coupled with resistance-enhancing activity and altered microtubule association of a phosphomimetic mutation in the pseudokinase domain ofAtMLKL1, point to a cell death-independent immunity mechanism.One Sentence SummaryPlants have a protein family that is structurally homologous to vertebrate mixed lineage kinase domain-like protein, which induces necroptotic cell death, but these plant proteins can confer immunity without host cell death.