ZAR Wars: Characterising New Motifs in the Atypically Ancient Immune Receptor, ZAR1

The nucleotide-binding leucine rich repeat (NLR) protein family plays a key role in plant innate immunity, detecting pathogens and triggering immunity. Following effector perception, NLR proteins are activated and form high-order oligomeric complexes termed resistosomes. These resistosomes mediate disease resistance often with the induction of a programmed cell death, termed the hypersensitive response. ZAR1 is an atypically conserved coiled-coil (CC)- type NLR that traces its origin to early flowering plant lineages. The N-terminus of ZAR1 contains a key sequence signature known as the MADA motif, which is conserved in 20% of angiosperm CC-NLRs and is necessary for immune signalling and cell death. We recently identified a novel conserved surface on the activated ZAR1 resistosome. The surface is formed by a consensus sequence pattern termed the underside (UND) motif and is required for ZAR1- mediated cell death. However, the exact role of the MADA and UND motifs in ZAR1-mediated immune responses and downstream signalling remains largely unknown. In this study, we performed RNA-seq to determine whether the MADA and UND motifs play a role in ZAR1-mediated transcriptional reprogramming in Nicotiana benthamiana. Our analyses identified differentially regulated genes following ZAR1 activation. Strikingly, we observed that the transcriptional changes are suppressed when either the MADA or UND motif of ZAR1 is mutated. We therefore conclude that both MADA and UND motifs are equally required for the transcriptional regulation by the ZAR1 resistosome. In the future we aim to use biochemical and cell biology approaches to further study the role of these motifs in ZAR1 activation and signalling.