两类免疫受体强强联手筑牢植物免疫防线

植物先天免疫系统在抵御病原菌入侵过程中发挥至关重要的作用, 主要包括两个层次, 即病原菌相关分子模式和效应因子分别触发的PTI和ETI免疫反应。PTI和ETI分别由植物细胞膜表面模式识别受体(PRRs)和胞内免疫受体(NLRs)激活, 具有特异的激活机制, 但是两者激活的下游免疫事件相互重叠。PTI和ETI是否为泾渭分明的两道防线, 以及ETI与PTI下游事件为何如此相似, 一直是植物免疫领域最受关注的问题之一。最近, 中国科学院分子植物科学卓越创新中心辛秀芳团队与合作者利用拟南芥(Arabidopsis thaliana)与丁香假单胞杆菌(Pseudomonas syringae)互作系统对PTI和ETI在机制上的联系进行了研究。他们发现PRRs和共受体参与ETI, 而活性氧的产生是联系PRRs和NLRs所介导的免疫早期信号事件。他们还发现NLRs信号能够迅速增强PTI关键因子的转录和蛋白水平, PTI的增强在ETI免疫反应中不可或缺。该研究从机制上解析了植物免疫领域中长期悬而未决的PTI与ETI相似性之谜, 是该领域的一项突破性进展, 为未来作物分子设计育种提供了新的启示。     

水稻免疫机制研究进展

植物先天免疫主要由两部分组成：一类是通过细胞膜上的病原菌分子模式识别受体识别病原微生物表面存在的分子特征激发的免疫反应（PTI）;另一类是专化性的抗病R蛋白识别病原微生物的效应蛋白,从而激发下游的病原菌小种特异性的防卫反应过程（ETI）．随着水稻抗病信号途径中越来越多的抗病基因以及关键的调控基因被克隆和功能鉴定,同时多种水稻病原菌效应蛋白的发现,水稻抗病机理的研究也越来越深入．本文阐述了水稻的PTI,ETI及其下游参与免疫信号转导的关键性组分,从而形成一个初步的水稻免疫调控网络．     

模式识别受体的胞内转运及其在植物免疫中的作用

植物利用细胞表面模式识别受体(PRRs)来感知病原相关分子模式(PAMPs), 进而触发自身的免疫反应(PTI)。在植物免疫过程中, PRRs在细胞内的正确定位对其生理功能的发挥至关重要。PRRs蛋白可以在内质网(ER)上合成, 并通过胞吐被分泌到质膜(PM)上。此外, PRRs蛋白也可以通过胞吞进行胞内循环或降解。细胞可以通过胞内转运降解PRRs蛋白以终止信号转导, 也可以通过形成胞内体进行信号传递。该文概述了PRRs蛋白及其配体的研究进展以及PRRs蛋白的胞内转运在植物免疫中的重要作用。     

模式识别受体的胞内转运及其在植物免疫中的作用

植物利用细胞表面模式识别受体(PRRs)来感知病原相关分子模式(PAMPs),进而触发自身的免疫反应(PTI)。在植物免疫过程中,PRRs在细胞内的正确定位对其生理功能的发挥至关重要。PRRs蛋白可以在内质网(ER)上合成,并通过胞吐被分泌到质膜(PM)上。此外, PRRs蛋白也可以通过胞吞进行胞内循环或降解。细胞可以通过胞内转运降解PRRs蛋白以终止信号转导,也可以通过形成胞内体进行信号传递。该文概述了PRRs蛋白及其配体的研究进展以及PRRs蛋白的胞内转运在植物免疫中的重要作用。     

基于模式识别受体和人工设计诱饵蛋白扩展植物识别特异性

病原/微生物相关分子模式(PAMPs/MAMPs)被位于宿主细胞表面的模式识别受体(PRRs)识别并激活免疫反应.这种病原相关分子模式触发的免疫反应(PTI)能够帮助植物抵抗大部分致病微生物的侵入,因此利用基因工程技术在植物中表达PRRs,以增强植物对病原微生物的免疫识别是一种非常有潜力的植物抗病性改良的策略.植物病原微生物分泌的效应蛋白通常利用多种多样的生化机制直接靶向和抑制PTI信号通路的关键组分,从而抑制PTI.一些植物进化出与效应蛋白的靶标类似的诱饵蛋白,并诱导效应蛋白的错误靶向.这种识别的结果不抑制PTI免疫反应,反而诱导效应蛋白激活的免疫反应(ETI).这种机制提示了人工设计的诱饵蛋白在特定植物中产生新的识别特异性的可能性.本综述总结了PRRs对PAMPs的识别,以及诱饵蛋白对效应蛋白监控方面的研究进展.利用转基因异源表达EFR或PBS1诱饵蛋白在实验室条件下成功扩展了植物的识别特异性,体现了对PRRs和人工设计的诱饵蛋白在植物对病原识别特异性的扩展和抗病性改良方面的潜力,突显了分离和鉴定新的PRRs和诱饵蛋白的必要性.     

植物与病原菌互作的分子机制研究进展

植物的先天免疫主要包括模式识别受体对保守的微生物病原相关分子模式的识别和抗病蛋白对效应蛋白的识别。植物与病原体互作过程中存在广泛的信号交流,信号分子在植物与病原体的互作攻防中发挥了重要的调控作用,决定了二者的竞争关系。当前,大量植物与病原体互作中的信号分子被定位和克隆,其作用方式被揭示。本文总结了这些信号分子及其在植物免疫过程中的作用机制,主要包括植物细胞表面的模式识别受体分子对病原相关分子模式的识别与应答,植物抗病蛋白对病原体效应蛋白的识别与应答,以及免疫反应下游相关信号分子及其在植物抗病中的作用。此外,本文对未来相关研究提出了展望。     

鱼类模式识别受体的研究进展

天然免疫（innate immunity）是基于对病原微生物成分的非克隆性识别而启动的快速防御反应。天然免疫系统可通过胚系编码的模式识别受体（pattern-recognition receptors,PRR）识别恒定不变的病原基元,即病原相关分子模式（pathogen-associated molecular patterns,PAMPs）,启动信号级联转导,最终PRRs信号激活宿主免疫和前炎性基因的表达,引发针对所识别病原的免疫反应。目前PRRs主要分为5类,即C-型Lectins、Toll样受体（Toll-like receptors,TLRs）、视黄酸诱导基因I样受体（retinoic acid inducible gene I-like receptors,RLRs）、包含核苷酸结合区和亮氨酸富集区蛋白（the nucleotide-binding domain,leucine-rich repeatcontaining proteins,NLRs,也称NOD样受体）和最近发现的AIM样受体（absent in melanoma（AIM）-like receptors,ALRs）。近年来,随着5种鱼类基因组序列草图的完成,大量鱼类PRRs基因被发现,一些PRRs的配体特异性及其相关信号途径正在逐渐明晰。为此,将对鱼类Toll样受体（TLRs）、视黄酸诱导基因I样受体（RLRs）和NOD样受体（NLRs）的研究进展进行综述。     

TANK结合激酶1在固有免疫应答中的作用及其泛素化调控

固有免疫系统通过模式识别受体识别病原微生物表面的病原相关分子模式启动固有免疫反应,经级联信号转导,激活下游转录因子NF-κB和干扰素调节因子IRFs,进而产生炎性细胞因子以及Ⅰ型干扰素,抵抗病原微生物感染。TANK结合激酶1 (TANK binding kinase 1,TBK1) 作为一个中心节点蛋白,参与多条固有免疫信号通路的传导,可同时激活NF-κB和IRFs,是机体抗感染过程中关键的蛋白激酶。TBK1的精准调控对维持机体免疫稳态、抵抗病原体入侵至关重要。文中综述了TBK1在固有免疫应答中的作用及其泛素化调控机制,以期为病原体感染及自身免疫病的临床治疗提供理论基础。     

无脊椎动物清道夫受体的免疫调控

在长期进化的过程中,无脊椎动物逐渐形成了受体识别-信号传导-免疫应答为特征的天然免疫体系,以清除凋亡细胞或外界的病原微生物。清道夫受体（SRs）是一类位于细胞表面的跨膜受体,也是一类参与无脊椎动物天然免疫反应的重要模式识别受体。清道夫受体参与免疫反应的异己靶标识别,通过下游信号级联调控抗菌肽合成和吞噬作用。本文综述了无脊椎动物清道夫受体的种类、结构及其参与天然免疫的调控机制,探讨了无脊椎动物清道夫受体研究中尚待解决的问题。     

miRNA对固有免疫信号通路调控的研究进展

小RNA(miRNA)作为一种小分子非编码RNA,通过抑制表达或降解靶基因mRNA的方式对目标基因进行调控,参与多种生理和病理过程.随着对miRNA的深入研究发现,miRNA可通过调控免疫通路及通路中的免疫因子影响免疫进程.Toll样受体(TLR)、维甲酸诱导基因Ⅰ样受体(RLRs)和核苷酸结合寡聚化结构域样受体(NLRs)作为固有免疫模式识别受体(PRR)重要成员,在识别病原及诱导下游免疫因子抵抗病原入侵方面有重要作用,本文将就miRNA对TLR,RLRs,NLRs固有免疫信号调控方式及结果的最新研究进行总结,为深入研究miRNA对固有免疫调控作用提供参考.     

Molecular insights into the biochemical functions and signalling mechanisms of plant NLRs

Plant intracellular immune receptors known as NLR (nucleotide-binding leucine-rich repeat) proteins confer immunity and cause cell death. Plant NLR proteins that directly or indirectly recognize pathogen effector proteins to initiate immune signalling are regarded as sensor NLRs. Some NLR protein families function downstream of sensor NLRs to transduce immune signalling and are known as helper NLRs. Recent breakthrough studies on plant NLR protein structures and biochemical functions greatly advanced our understanding of NLR biology. Comprehensive and detailed knowledge on NLR biology requires future efforts to solve more NLR protein structures and investigate the signalling events between sensor and helper NLRs, and downstream of helper NLRs.     

Plant systems for recognition of pathogen-associated molecular patterns

Research of the last decade has revealed that plant immunity consists of different layers of defense that have evolved by the co-evolutional battle of plants with its pathogens. Particular light has been shed on PAMP- (pathogen-associated molecular pattern) triggered immunity (PTI) mediated by pattern recognition receptors. Striking similarities exist between the plant and animal innate immune system that point for a common optimized mechanism that has evolved independently in both kingdoms. Pattern recognition receptors (PRRs) from both kingdoms consist of leucine-rich repeat receptor complexes that allow recognition of invading pathogens at the cell surface. In plants, PRRs like FLS2 and EFR are controlled by a co-receptor SERK3/BAK1, also a leucine-rich repeat receptor that dimerizes with the PRRs to support their function. Pathogens can inject effector proteins into the plant cells to suppress the immune responses initiated after perception of PAMPs by PRRs via inhibition or degradation of the receptors. Plants have acquired the ability to recognize the presence of some of these effector proteins which leads to a quick and hypersensitive response to arrest and terminate pathogen growth.     

Engineering plant resistance by constructing chimeric receptors that recognize damage-associated molecular patterns (DAMPs)

An efficient sensing of danger and a rapid activation of the immune system are crucial for the survival of plants. Conserved pathogen/microbe-associated molecular patterns (PAMPs/MAMPs) and endogenous molecular patterns, which are present only when the tissue is infected or damaged (damage-associated molecular patterns or DAMPs), can act as danger signals and activate the plant immune response. These molecules are recognized by surface receptors that are indicated as pattern recognition receptors (PRRs). In this paper we summarize recent information on oligogalacturonides (OGs), a class of DAMPs that is released from the extracellular matrix of the plant cell during pathogen attack or wounding. We also describe the characteristics of the Arabidopsis Wall-Associated Kinase 1 (WAK1), a PRR recently identified as a receptor of OGs and discuss the use of WAK1, PRRs and chimeric receptors to engineer resistance in crop plants.     

Enemy at the gates: traffic at the plant cell pathogen interface

The plant apoplast constitutes a space for early recognition of potentially harmful non-self. Basal pathogen recognition operates via dynamic sensing of conserved microbial patterns by pattern recognition receptors or of elicitor-active molecules released from plant cell walls during infection. Recognition elicits defence reactions depending on cellular export via SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex-mediated vesicle fusion or plasma membrane transporter activity. Lipid rafts appear also involved in focusing immunity-associated proteins to the site of pathogen contact. Simultaneously, pathogen effectors target recognition, apoplastic host proteins and transport for cell wall-associated defence. This microreview highlights most recent reports on the arms race for plant disease and immunity at the cell surface.     

Plant immune signaling: Advancing on two frontiers

Plants have evolved multiple defense strategies to cope with pathogens, among which plant immune signaling that relies on cell-surface localized and intracellular receptors takes fundamental roles. Exciting breakthroughs were made recently on the signaling mechanisms of pattern recognition receptors(PRRs) and intracellular nucleotide-binding site(NBS) and leucine-rich repeat(LRR)domain receptors(NLRs). This review summarizes the current view of PRRs activation, emphasizing the most recent discoveries about PRRs’ dynamic regulation and signaling mechanisms directly leading to downstream molecular events including mitogen-activated protein kinase(MAPK) activation and calcium(Ca2+) burst. Plants also have evolved intracellular NLRs to perceive the presence of specific pathogen effectors and trigger more robust immune responses. We also discuss the current understanding of the mechanisms of NLR activation, which has been greatly advanced by recent breakthroughs including structures of the first full-length plant NLR complex, findings of NLR sensor-helper pairs and novel biochemical activity of Toll/interleukin-1 receptor(TIR) domain.     

A novel allele of the Arabidopsis thaliana MACPF protein CAD1 results in deregulated immune signaling

Immune recognition in plants is governed by two major classes of receptors: pattern recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat receptors (NLRs). Located at the cell surface, PRRs bind extracellular ligands originating from microbes (indicative of “non-self”) or damaged plant cells (indicative of “infected-self”), and trigger signaling cascades to protect against infection. Located intracellularly, NLRs sense pathogen-induced physiological changes and trigger localized cell death and systemic resistance. Immune responses are under tight regulation in order to maintain homeostasis and promote plant health. In a forward-genetic screen to identify regulators of PRR-mediated immune signaling, we identified a novel allele of the membrane-attack complex and perforin (MACPF)-motif containing protein CONSTITUTIVE ACTIVE DEFENSE 1 (CAD1) resulting from a missense mutation in a conserved N-terminal cysteine. We show that cad1-5 mutants display deregulated immune signaling and symptoms of autoimmunity dependent on the lipase-like protein ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), suggesting that CAD1 integrity is monitored by the plant immune system. We further demonstrate that CAD1 localizes to both the cytosol and plasma membrane using confocal microscopy and subcellular fractionation. Our results offer new insights into immune homeostasis and provide tools to further decipher the intriguing role of MACPF proteins in plants.     

Microbe-derived non-necrotic glycoside hydrolase family 12 proteins act as immunogenic signatures triggering plant defenses

Plant pattern recognition receptors(PRRs) are sentinels at the cell surface sensing microbial invasion and activating innate immune responses. During infection, certain microbial apoplastic effectors can be recognized by plant PRRs, culminating in immune responses accompanied by cell death. However, the intricated relationships between the activation of immune responses and cell death are unclear.Here, we studied the glycoside hydrolase family12(GH12) protein, Ps109281, secreted by Phytophthora ...     

Molecular sensors for plant immunity; pattern recognition receptors and race-specific resistance proteins

Plants have to molecularly sense invasions from pathogenic microbes to activate their built-in immune responses. There are two different types of sensor proteins, called immune receptors. They are the indispensible molecular instruments to perceive non-self molecules derived from microbes. A genetic defect of the immune receptors fails to activate immune responses, consequently resulting in disease susceptibility. In general, membrane-bound immune receptors, known to be pattern recognition receptors and exposed on the outside of the cell, recognize microbe-associated molecular patterns from pathogens. Intracellular immune receptors, also called plant disease resistance proteins, directly perceive pathogen-derived effectors or indirectly recognize the effector-mediated modification of host proteins inside the cells. In this review, we introduce the classes and functions of pattern recognition receptors that were molecularly identified so far. Additionally, we summarize recent progresses in structural functions and molecular dynamics of the plant disease resistance proteins.     

开启防御之门: 植物抗病小体

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。