Arabidopsis NIM1-INTERACTING1 (NIMIN1) is a multi-domain protein controlling transition from systemic acquired resistance (SAR) to cell death

NIM1-INTERACTING (NIMIN) proteins were identified by interaction with the systemic acquired resistance (SAR) key regulator NPR1. The Arabidopsis family comprises four related, yet distinct members. Ample evidence predicts that NIMIN1 is a multi-domain protein which comes into action after the onset of salicylic acid (SA) signaling prior to induction of the PR-1 defense gene. Bioinformatics, protein-protein interaction assays and expression studies in tobacco were applied to explore functions of NIMIN1. The N-terminal sequence encompassing amino acids 1 to 15 conveyed accumulation of NIMIN1 protein in planta. This newly identified segment and the known conserved NIMIN1 domains, i.e., two distinct NPR1 binding sites and an EAR motif, are neatly separated from each other by disordered regions. Co-expression of NIMIN1 and NPR1 reinforced accumulation of NPR1 protein while ectopic overexpression of NIMIN1 promoted emergence of cell death driven by the EAR motif and disturbed development of tobacco plants. We suggest that NIMIN1 acts as a dynamic signaling agent controlling transition of pathogen-infected leaves from survival to tissue collapse. Initially, NIMIN1 binding renders the NPR1 transcription complex sensitive to the SAR signal SA enabling PR-1 transcription. At high levels of SA, NIMIN1 is outcompeted by SA from the NPR1 C-terminus, and accumulating NIMIN1 engages via its EAR motif with TOPLESS-RELATED3, thereby affecting global hormone signaling and inducing cell death in severely endangered tissue.