Genome-wide expression analysis of immune receptors in hot pepper reveals an autonomous NLR cluster in higher plants

Plants possess hundreds of intracellular immune receptors encoding nucleotide-binding domain and leucine-rich repeat (NLR) proteins. Autoactive NLRs, in some cases, a specific domain of NLR, induce plant cell death in absence of pathogen infection. In this study, we identified a group of NLRs (G10) carrying autoactive coiled-coil (CC) domains in pepper (Capsicum annuum L. cv. CM334) by genome-wide transient expression analysis. The G10-CC-mediated cell death mimics the HR cell death triggered by interaction between NLR and effecter. Sequence alignment and mutagenesis analyses revealed that the intact form of α1 helix in G10-CC domain is critical for both G10-CC- and R gene-mediated HR cell death. We also found that G10-CCs are localized in plasma membrane as like the Arabidopsis singleton NLR ZAR1. Extended studies revealed that the G10-CCs in other Solanaceae plants including tomato, potato, and tobacco as well as a monocot plant, rice induce cell death by heterologous expression in Nicotiana benthamiana. Furthermore, the cell death induced by G10-CCs does not require known helper NLRs, implying that G10-NLRs are novel singleton NLRs. Our studies not only uncover the general function of CNL-induced cell death throughout mono- and dicot plants but also provides powerful resources to dissect the underlying molecular mechanism of NLR-mediated cell death in plants.