开启防御之门: 植物抗病小体

doi:10.11983/CBB19035

摘要/Abstract

摘要： NLR蛋白是存在于植物和动物中的一个免疫受体大家族, 具有核苷酸结合域并富含亮氨酸重复序列。植物NLR通过识别病原菌特异效应子开启免疫信号转导。第1个植物NLR抗性蛋白于25年前克隆, 但其激活机制仍不清楚, 至今仍未获得一个完整的NLR蛋白结构。最近, 柴继杰、周俭民和王宏伟实验室合作解析了第一个植物完整NLR ZAR1激活前后的结构, 研究成果以两篇论文形式发表在“科学”杂志上, 填补了NLR介导的免疫信号转导研究领域的空白。该文简要总结了相关研究进展, 讨论了NLR免疫信号转导研究领域尚需解决的问题。

关键词: 植物免疫, NLR, ZAR1, 变构激活, 抗病小体

Abstract: Nucleotide binding, leucine-rich repeat (NLR) immune receptors are a major family of plant resistance (R) proteins, which are also found in animals. NLRs turn on immune signaling by recognizing pathogen-specific effectors in plants. Although the first few plant NLR R genes were cloned more than 25 years ago, the activation mechanism remained elusive. No structure is available for the full-length plant NLRs despite attempts over the last 2 decades. Recently, studies from the Chai, Zhou and Wang labs, published in Science, solved the structure of zygote arrest 1 (ZAR1) before and after effector recognition, which fills a huge gap in NLR biology. This mini review briefly summarized these findings and related progresses, and highlighted further challenges in NLR-mediated immune signaling field.

Key words: plant immunity, NLR, ZAR1, allosteric activation, resistosome

夏石头, 李昕. 开启防御之门: 植物抗病小体. 植物学报, 2019, 54(3): 288-292.

Shitou Xia, Xin Li. Open a Door of Defenses: Plant Resistosome. Chinese Bulletin of Botany, 2019, 54(3): 288-292.

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链接本文: https://www.chinbullbotany.com/CN/10.11983/CBB19035

https://www.chinbullbotany.com/CN/Y2019/V54/I3/288

图/表 1

图1 PBL2UMP诱导的ZAR1抗性小体的激活与装配野油菜黄单胞菌的效应蛋白AvrAC以尿苷酰化修饰拟南芥PBL2激酶, 尿苷酰化的PBL2UMP作为配体通过与RKS1互作而被ZAR1-RKS1复合物招募。RKS1的激活片段在与PBL2UMP的2个尿苷基部分(球形)相互作用后变得稳定(橙色表面), 并与ZAR1NBD结构域发生立体碰撞, 导致后者向外旋转, 从而释放ADP, 形成可与dATP/ATP结合的中间状态ZAR1-RKS1-PBL2UMP复合体。该复合物结合dATP/ATP后, 诱导ZAR1结构重塑和折叠转换, 隐藏在非活性ZAR1-RKS1复合物中的ZAR1的N顶末端α-螺旋(α1, 红色)暴露在溶剂中, 导致ZAR1完全激活(激活态ZAR1-RKS1-PBL2UMP), 继而通过多聚化形成五聚轮状结构的ZAR1抗性小体(紫色方框内突出显示形成的漏斗状结构)。CC、NBD、HD1、WHD和LRR为ZAR1的不同结构域。

Figure 1 PBL2UMP-induced activation and assembly of the ZAR1 resistosome Arabidopsis PBL2 is modified by uridylyl transferase AvrAC, which is an effector protein from Xanthomonas campestris. The uridylylated PBL2 (PBL2UMP) as a ligand is then recruited by the ZAR1-RKS1 complex through interaction with the pseudokinase RKS1. The activation segment of RKS1 becomes stabilized (orange surface) after interacting with the two uridylyl moieties (in sphere) of PBL2UMP, and sterically clashes with ZAR1NBD, causing the latter to rotate outward and consequently release ADP, forming an intermediate ZAR1-RKS1-PBL2UMP complex which allows it to bind dATP/ATP. Binding of dATP/ATP induces structural remodeling and fold switching of ZAR1. The very N-terminal helix (α1, red) of ZAR1 buried in the inactive ZAR1-RKS1 complex becomes solvent-exposed in the activated ZAR1-RKS1-PBL2UMP complex, forming a ZAR1 resistosome pentameric structure through polymerization (a funnel-shaped structure highlighted within the purple frame). CC, NBD, HD1, WHD and LRR are different structural domains of ZAR1.

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