Plant NLR immune receptor Tm-22 activation requires NB-ARC domain-mediated self-association of CC domain

Abstract

The nucleotide-binding, leucine-rich repeat-containing (NLR) class of immune receptors of plants and animals recognize pathogen-encoded proteins and trigger host defenses. Although animal NLRs form oligomers upon pathogen recognition to activate downstream signaling, the mechanisms of plant NLR activation remain largely elusive. Tm-2² is a plasma membrane (PM)-localized coiled coil (CC)-type NLR and confers resistance to Tobacco mosaic virus (TMV) by recognizing its viral movement protein (MP). In this study, we found that Tm-2² self-associates upon recognition of MP. The CC domain of Tm-2² is the signaling domain and its function requires PM localization and self-association. The nucleotide-binding (NB-ARC) domain is important for Tm-2² self-interaction and regulates activation of the CC domain through its nucleotide-binding and self-association. (d)ATP binding may alter the NB-ARC conformation to release its suppression of Tm-2² CC domain-mediated cell death. Our findings provide the first example of signaling domain for PM-localized NLR and insight into PM-localized NLR activation. Nucleotide-binding, leucine-rich repeat proteins (NLR) can function as immune receptors of plants and animals and confer resistance against pathogens. However, despite their importance in immunity, the activation mechanism of PM-localized NLRs remains largely elusive. In this study, we demonstrate that CC domain is the signaling domain for inducing cell death for PM-localized NLR Tm-2². Further, we report that nucleotide-binding (NB-ARC) domain is important for Tm-2² self-association and regulates activation of CC domain through its nucleotide-binding and self-association. Our findings provide the first example of signaling domain for PM-localized NLR and insight into PM-localized NLR activation.