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Tetrameric immune receptors Nucleotide-binding/leucine-rich repeat (NLR) immune receptors detect pathogen effectors and trigger a plant's immune response. Two groups have now defined the structures of two NLRs that carry Toll-like interleukin-1 receptor (TIR) domains (TIR-NLRs) (see the Perspective by Tian and Li). Ma et al. studied the Arabidopsis thaliana TIR-NLR RPP1 (recognition of Peronospora parasitica 1) and its response to effectors from an oomycete pathogen. Martin et al. studied the Nicotiana benthamiana TIR-NLR ROQ1 (recognition of XopQ 1) and its response to the Xanthomonas effector. Both groups found that these TIR-NLRs formed tetramers that, when activated by binding to the pathogen effector, exposed the active site of a nicotinamide adenine dinucleoside (NAD) hydrolase. Thus, recognition of the pathogen effector initiates NAD hydrolysis and begins the immune response. Science , this issue p. eabe3069 , p. eabd9993 ; see also p. 1163
ShouCai et al. (Fri,) studied this question.