Cell Host & Microbe
Volume 28, Issue 6, 9 December 2020, Pages 813-824.e6
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Article
Discovery of a Family of Mixed Lineage Kinase Domain-like Proteins in Plants and Their Role in Innate Immune Signaling

https://doi.org/10.1016/j.chom.2020.08.012Get rights and content
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Highlights

  • Plant genomes encode a family of proteins resembling animal necroptosis mediator MLKL

  • Arabidopsis MLKLs (AtMLKLs) promote pathogen resistance mediated by TIR-type NLRs

  • Cryo-EM structure of AtMLKL reveals tetramers, which represents an auto-repressed state

  • AtMLKLs HeLo domain can elicit cell death but this is dispensable for immune function

Summary

HeLo domain-containing mixed lineage kinase domain-like protein (MLKL), a pseudokinase, mediates necroptotic cell death in animals. Here, we report the discovery of a conserved protein family across seed plants that structurally resembles vertebrate MLKL. The Arabidopsis genome encodes three MLKLs (AtMLKLs) with overlapping functions in disease resistance mediated by Toll-interleukin 1-receptor domain intracellular immune receptors (TNLs). The HeLo domain of AtMLKLs confers cell death activity but is dispensable for immunity. Cryo-EM structures reveal a tetrameric configuration, in which the HeLo domain is buried, suggestive of an auto-repressed complex. The mobility of AtMLKL1 along microtubules is reduced by chitin, a fungal immunity-triggering molecule. An AtMLKL1 phosphomimetic variant exhibiting reduced mobility enhances immunity. Coupled with the predicted presence of HeLo domains in plant helper NLRs, our data reveal the importance of HeLo domain proteins for TNL-dependent immunity and argue for a cell death-independent immune mechanism mediated by MLKLs.

Keywords

MLKL
necroptosis
Cell death
HeLo domain
toll-interleukin1-receptor domain intracellular immune receptors
cryo-electron microscopy structures
microtubules

Cited by (0)

10

These authors contributed equally

11

Present address: Institute for Plant Sciences, University of Cologne, Cologne 50674, Germany

12

Present address: PalmElit Sas, F-34980 Montferrier-sur-Lez, France

13

Present address: Institute for Biological Physics, University of Cologne, Cologne 50937, Germany

14

Lead Contact