RESUMO
Plant and animal intracellular nucleotide-binding, leucine-rich repeat (NLR) immune receptors detect pathogen-derived molecules and activate defense. Plant NLRs can be divided into several classes based upon their N-terminal signaling domains, including TIR (Toll-like, Interleukin-1 receptor, Resistance protein)- and CC (coiled-coil)-NLRs. Upon ligand detection, mammalian NAIP and NLRC4 NLRs oligomerize, forming an inflammasome that induces proximity of its N-terminal signaling domains. Recently, a plant CC-NLR was revealed to form an inflammasome-like hetero-oligomer. To further investigate plant NLR signaling mechanisms, we fused the N-terminal TIR domain of several plant NLRs to the N terminus of NLRC4. Inflammasome-dependent induced proximity of the TIR domain in planta initiated defense signaling. Thus, induced proximity of a plant TIR domain imposed by oligomerization of a mammalian inflammasome is sufficient to activate authentic plant defense. Ligand detection and inflammasome formation is maintained when the known components of the NLRC4 inflammasome is transferred across kingdoms, indicating that NLRC4 complex can robustly function without any additional mammalian proteins. Additionally, we found NADase activity of a plant TIR domain is necessary for plant defense activation, but NADase activity of a mammalian or a bacterial TIR is not sufficient to activate defense in plants.
Assuntos
Proteínas NLR , Imunidade Vegetal , Proteínas de Plantas , Proteínas Recombinantes de Fusão , Transdução de Sinais , Animais , Inflamassomos/genética , Inflamassomos/imunologia , Inflamassomos/metabolismo , Mamíferos , Proteínas NLR/química , Proteínas NLR/genética , Proteínas NLR/imunologia , Proteínas NLR/metabolismo , Imunidade Vegetal/genética , Imunidade Vegetal/imunologia , Proteínas de Plantas/química , Proteínas de Plantas/genética , Proteínas de Plantas/imunologia , Proteínas de Plantas/metabolismo , Domínios Proteicos/genética , Domínios Proteicos/fisiologia , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/imunologia , Proteínas Recombinantes de Fusão/metabolismo , Transdução de Sinais/genética , Transdução de Sinais/imunologiaRESUMO
Most land plant genomes carry genes that encode RPW8-NLR Resistance (R) proteins. Angiosperms carry two RPW8-NLR subclasses: ADR1 and NRG1. ADR1s act as 'helper' NLRs for multiple TIR- and CC-NLR R proteins in Arabidopsis. In angiosperm families, NRG1 co-occurs with TIR-NLR Resistance (R) genes. We tested whether NRG1 is required for signalling of multiple TIR-NLRs. Using CRISPR mutagenesis, we obtained an nrg1a-nrg1b double mutant in two Arabidopsis accessions, and an nrg1 mutant in Nicotiana benthamiana. These mutants are compromised in signalling of all TIR-NLRs tested, including WRR4A, WRR4B, RPP1, RPP2, RPP4 and the pairs RRS1/RPS4, RRS1B/RPS4B, CHS1/SOC3 and CHS3/CSA1. In Arabidopsis, NRG1 is required for the hypersensitive cell death response (HR) and full oomycete resistance, but not for salicylic acid induction or bacterial resistance. By contrast, nrg1 loss of function does not compromise the CC-NLR R proteins RPS5 and MLA. RPM1 and RPS2 (CC-NLRs) function is slightly compromised in an nrg1 mutant. Thus, NRG1 is required for full TIR-NLR function and contributes to the signalling of some CC-NLRs. Some NRG1-dependent R proteins also signal partially via the NRG1 sister clade, ADR1. We propose that some NLRs signal via NRG1 only, some via ADR1 only and some via both or neither.
