Many proteins involved in cell death execution or cell death-associated immunity in plants, animals and fungi are characterised by the presence of a four-helical bundle structure named the HeLo domain after the fungal HET and LOPB proteins. One salient example of a HeLo domain-containing protein is MLKL (mixed lineage kinase domain-like protein), which mediates necroptosis in vertebrates.
We recently discovered a conserved protein family across seed plants that structurally and functionally resembles the animal necroptosis mediator MLKL. The Arabidopsis thaliana genome encodes three MLKLs (AtMLKLs) with overlapping functions in disease resistance mediated by Toll-interleukin 1-receptor domain intracellular immune receptors (TNLs). AtMLKLs contain an N-terminal helical bundle, termed the HeLo domain, which confers cell death activity, yet is dispensable for AtMLKL-dependent immunity. Based on the current understanding of the mode of action of animal MLKL, we hypothesise that animal and plant MLKLs share a common mechanism defined by oligomerisation and translocation to the plasma membrane, ultimately leading to plasma membrane damage, cell death and immunity. However, the molecular mechanisms of how plant and animal MLKL induce cell death remains unknown. We aim to understand the molecular principles of MLKL-mediated cell death and immunity by determining and comparing the nanoscale organization and cellular dynamics of this protein family in plant and animal cells.