Disentangling cause and consequence: Genetic dissection of the DANGEROUS MIX2 risk locus, and activation of the DM2h NLR in autoimmunity
Nucleotide-binding domain-leucine-rich repeat-type immune receptors (NLRs) protect plants against pathogenic microbes through intracellular detection of effector proteins. However, this comes at a cost, as NLRs can also induce detrimental autoimmunity in genetic interactions with foreign alleles. This may occur when independently evolved genomes are combined in inter- or intraspecific crosses, or when foreign alleles are introduced by mutagenesis or transgenesis. Most autoimmunity-inducing NLRs are encoded within highly variable NLR gene clusters with no known immune functions, which were termed autoimmune risk loci. Whether risk NLRs differ from sensor NLRs operating in natural pathogen resistance and how risk NLRs are activated in autoimmunity is unknown. Here, we analyzed the DANGEROUS MIX2 risk locus, a major autoimmunity hotspot in Arabidopsis thaliana. By gene editing and heterologous expression, we show that a single gene, DM2h, is necessary and sufficient for autoimmune induction in three independent cases of autoimmunity in accession Landsberg erecta. We focus on autoimmunity provoked by an EDS1-YFPNLS fusion protein to functionally characterize DM2h and determine features of EDS1-YFPNLS activating the immune receptor. Our data suggest that risk NLRs function reminiscent of sensor NLRs, while autoimmunity-inducing properties of EDS1-YFPNLS are in this context unrelated to the proteins functions as immune regulator. We propose that autoimmunity may, at least in some cases, be caused by spurious, stochastic interactions of foreign alleles with co-incidentally matching risk NLRs.