背景回顾：Plant nucleotide-binding leucine-rich repeat-containing (NLR) receptors with an N-terminal Toll/interleukin-1 receptor (TIR) domainsense pathogen effectors to enable TIR-encoded NADase activity for immune signaling. TIR-NLR signaling requires helper NLRs N requirement gene 1 (NRG1) and Activated Disease Resistance 1 (ADR1), and Enhanced Disease Susceptibility 1 (EDS1) that forms a heterodimer with each of its paralogs Phytoalexin Deficient 4 (PAD4) and Senescence-Associated Gene101 (SAG101). 

结果1-小分子配体鉴定：Here, we show that TIR-containing proteins catalyze production of 2'-(5′'-phosphoribosyl)-5′-adenosine mono-/di-phosphate (pRib-AMP/ADP) in vitro and in planta. 

结果1-小分子配体的作用：Biochemical and structural data demonstrate that EDS1-PAD4 is a receptor complex for pRib-AMP/ADP, which allosterically promote EDS1-PAD4 interaction with ADR1-L1 but not NRG1A. 

结论：Our study identifies TIR-catalyzed pRib-AMP/ADP as a missing link in TIR signaling via EDS1-PAD4 and as likely second messengers for plant immunity. 

 摘 要 

植物核苷酸结合、富含亮氨酸重复（NLR）受体包含一个TIR结构域用于感知病原物的效应子，从而使得TIR编码的NADase活性得以作用于植物的免疫信号转导。TIR-NLR信号转导需要helper NLRs蛋白NRG1和ADR1，并且EDS1会分别与其旁系同源物PAD4和SAG101形成异源二聚体。本文中，作者发现含有TIR结构域的蛋白能够在体外和植物体内，催化形成小分子pRib-AMP/ADP。生化实验和结构数据显示，小分子pRib-AMP/ADP会结合EDS1-PAD4受体复合物，并通过别构作用促进EDS1-PAD4与ADR1-L1，而非NRG1A的互作。本文的研究揭示了TIR催化的pRib-AMP/ADP是EDS1-PAD4介导的TIR信号转导中缺失的一环，作为第二信使作用于植物免疫。

 柴继杰