Abstract：
Nucleotide-binding domain and leucine-rich repeat (NLR) proteins with pathogen sensor activities have evolved to initiate immune signaling by activating helper NLRs. However, the mechanisms underpinning helper NLR activation by sensor NLRs remain poorly understood. Although coiled coil (CC) type sensor NLRs such as the Potato virus X disease resistance protein Rx have been shown to activate the oligomerization of their downstream helpers NRC2, NRC3 and NRC4, the domains involved in sensor-helper signaling are not known. Here, we used Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana to show that the nucleotide-binding (NB) domain within the NB-ARC of Rx is necessary and sufficient for oligomerization and immune signaling of downstream helper NLRs. In addition, the NB domains of the disease resistance proteins Gpa2 (cyst nematode resistance), Rpi-amr1, Rpi-amr3 (oomycete resistance) and Sw-5b (virus resistance) are also sufficient to activate their respective downstream NRC helpers. Using transient expression in the lettuce (Lactuca sativa), we show that Rx (both as full length or as NB domain truncation) and its helper NRC2 form a minimal functional unit that can be transferred from solanaceous plants (lamiids) to Campanulid species. Our results challenge the prevailing paradigm that NLR proteins exclusively signal via their N-terminal domains and reveal a signaling activity for the NB domain of NRC-dependent sensor NLRs. We propose a model in which helper NLRs can perceive the status of the NB domain of their upstream sensors.
摘要：
具有病原体传感器活性的核苷酸结合域和富含亮氨酸的重复（NLR）蛋白已经进化为通过激活辅助NLR来启动免疫信号。然而,传感器NLR激活辅助NLR的机制仍然知之甚少。尽管卷曲螺旋（CC）型传感器NLR（例如马铃薯X病毒抗病性蛋白Rx）已显示可激活其下游辅助子NRC2，NRC3和NRC4的寡聚化，但涉及传感器辅助信号传导的结构域尚不清楚。这里,我们使用根癌农杆菌介导的Nicotianabenthamiana瞬时表达表明，Rx的NB-ARC中的核苷酸结合（NB）结构域对于下游辅助NLR的寡聚化和免疫信号传导是必要和足够的。此外,抗病蛋白Gpa2（囊肿线虫抗性）的NB结构域，Rpi-amr1、Rpi-amr3(卵菌抗性)和Sw-5b(病毒抗性)也足以激活它们各自的下游NRC辅助体。使用生菜（Lactucasativa）中的瞬时表达，我们表明Rx（全长或NB结构域截短）及其辅助NRC2形成了一个最小的功能单元，可以从茄科植物（薄片）转移到Campanulid物种。我们的结果挑战了流行的范式，即NLR蛋白仅通过其N端结构域发出信号，并揭示了NRC依赖性传感器NLR的NB结构域的信号活性。我们提出了一个模型，在该模型中，助手NLR可以感知其上游传感器的NB域状态。
