植物抗病基因(R)与病原物无毒基因(Avr)相互作用机制的研究进展

PTI和ETI是植物在长期进化过程中形成的两类抵抗病原物的机制。基因对基因假说的抗病方式属于ETI抗性机制的一种,该假说认为具有保守NB-LRR结构域的R蛋白识别病原物非保守的无毒蛋白效应子(Avr),激活防卫反应信号途径,导致过敏性坏死。植物抗病基因(R)与病原菌无毒基因(Avr)产物间的直接或间接相互作用而产生的基因对基因抗性是植物抗病性的重要形式,该文对植物抗病蛋白与无毒蛋白相互作用机制进行了综述。其中,间接相互作用模式是主要方式。     

寄主植物与病原菌免疫反应的分子遗传基础

近年来,大量的植物抗病基因和病原菌无毒基因被克隆,抗病基因和无毒基因的结构、功能及其互作关系的研究也取得重大进展。在植物中,由病原菌模式分子(pathogen-associated molecular patterns, PAMPs)引发的免疫反应(PAMP-triggered immunity, PTI)和由效应因子引发的免疫反应(effector-triggered immunity, ETI)是植物在长期进化过程中形成的两类抵抗病原物的机制。PTI反应主要通过细胞表面受体(patternrecognition receptors, PRRs)识别并结合PAMPs从而激活下游免疫反应,而在ETI反应中,则通过植物R基因(resistance gene,R)与病原菌无毒基因(avirulence gene, Avr)产物间的直接或间接相互作用来完成免疫反应。本文对植物PTI反应和ETI反应分别进行了概述,重点探讨了植物R基因与病原菌Avr基因之间的互作遗传机理,并对目前植物抗性分子遗传机制研究和抗病育种中的问题进行了探讨和展望。     

植物抗病分子机制研究进展

近十年来,植物抗病分子机制研究取得显著进展.综述了植物抗病基因的克隆及其结构分析、病原菌无毒基因及其相关致病因子的克隆与研究、信号传导相关因子的克隆及其结构分析以及植物-病原菌的相互作用研究,重点介绍了以植物特异抗病基因为介导的诱导防卫作用机制(包括抗病基因编码毒素蛋白,进而抑制病原菌的繁殖;显性基因编码病原菌致病性的靶标物;抗病基因表达产物直接引发抗病反应和基因对基因的抗病作用机制等)的研究进展,以期为植物抗病育种提供有益的信息.     

植物抗病分子机制研究进展

近十年来,植物抗病分子机制研究取得显著进展。综述了植物抗病基因的克隆及其结构分析、病原菌无毒基因及其相关致病因子的克隆与研究、信号传导相关因子的克隆及其结构分析以及植物-病原菌的相互作用研究,重点介绍了以植物特异抗病基因为介导的诱导防卫作用机制(包括抗病基因编码毒素蛋白,进而抑制病原菌的繁殖;显性基因编码病原菌致病性的靶标物;抗病基因表达产物直接引发抗病反应和基因对基因的抗病作用机制等)的研究进展,以期为植物抗病育种提供有益的信息。     

植物TIR-NB-LRR类型抗病基因各结构域的研究进展

植物抗病反应是一个多基因调控的复杂过程,在这个过程中R基因发挥了非常重要的作用。根据其氨基酸基序组成以及跨膜结构域的不同,R基因可以分为多种类型,其中NBS-LRR类型是植物基因组中最大的基因家族之一。TIR-NB-LRR类型的抗病基因又是NB-LRR类型中的一大类,也是目前抗病基因研究的热点。该文总结了TIR-NB-LRR类型抗病基因各个结构域的功能和相关的研究进展。相关研究表明,TIR结构域主要通过自身或异源的二聚体化介导抗性信号的转导,但也有部分研究表明,该结构域可能参与病原菌的特异性识别。NBS结构域常被认为具有"分子开关"的功能,它可以通过结合ADP或ATP来调节植物抗病蛋白的构象变化,从而调节下游抗病信号的传导。LRR结构域在植物与病原菌互作的过程中可以通过与病原菌的无毒蛋白直接或间接互作来特异识别病原菌。也有研究发现,LRR结构域具有调节信号传导的功能。这些信息将为研究植物抗病机理提供理论依据,也为将来通过基因编辑技术对作物进行定向抗病育种提供思路。     

植物抗病基因同源序列及其在抗病基因克隆与定位中的应用

近10年来已有20多个植物抗病基因被克隆,测序,这些抗病基因所编码的蛋白中大多含有核苷酸结合位点,富含亮氨酸重复序列,蛋白激酶,亮氨酸拉链结构,跨膜结构域,Toll白介素－1区域等保守结构域。利用这些保守结构域合成PCR引物,已扩增出大量的植物抗病基因同源序列（RGA）。对RGA与抗病基因的关系进行了分析,讨论了RGA在研究抗病基因进化中的作用,指出RGA在抗病基因定位和转基因中具有重要意义。     

植物病原物无毒基因及其功能

植物抗病基因与病原物无毒基因产物间直接或间接相互作用导致产生的基因对基因抗性是植物抗病性的重要形式。无毒基因已在多种植物病原物 ,包括真菌、细菌、病毒和卵菌等中得到克隆。绝大多数已克隆无毒基因之间 ,及其与已知蛋白之间 ,均无显著序列同源性。然而 ,多数已克隆植物抗病基因有较高序列一致性 ,产物往往具有相似的结构域。由序列一致性很高的抗病基因产物与没有明显序列同源性的无毒基因产物相互作用 ,介导产生的过敏性细胞坏死和抗病性 ,在产生速度、强度和组织特异性等方面均可能有显著差异。无毒基因具有双重功能 :在含互补抗病基因植物中表现无毒效应 ,而在不含互补抗病基因植物中显示小种、菌株、致病型、或种特异性毒性效应     

植物抗病基因与病原菌无毒基因互作的分子基础

近10年来,大量的植物抗病基因和病原菌无毒基因被克隆,抗病基因和无毒基因的结构、功能及其互作关系的研究也取得重大进展。通过介绍抗病基因与无毒基因互作的两种模式,从抗病基因与病原菌无毒基因互作角度探讨了抗病基因在植物抗病育种和农作物生产中直用的问题,提出抗细菌和真菌单基因转化很难赋予农作物切实抗性。     

小麦新抗源贵农775抗条锈性特征与遗传分析

发掘并利用不同类型抗条锈病基因,构建区域间抗病基因多样性差异布局,是阻遏条锈菌大区域传播、实现小麦条锈病持续控制的重要策略。为了明确小麦新抗源贵农775抗条锈性特征和抗性遗传规律,为其合理布局应用提供依据,文章利用10个条锈菌菌系进行苗期分小种鉴定;构建贵农775与感病品种Avocet(S)杂交后代F2:3及回交BC1遗传群体,利用小麦条锈菌流行小种CYR32和最近发现的对Yr26基因有毒性的新致病类型CH42,对贵农775进行抗条锈性遗传分析。结果表明,贵农775对包括CH42致病类型在内的所有10个供试菌系均表现为免疫或近免疫的抗病性反应,而中国当前主要条锈病抗源品种92R137、川麦42(YrCH42)、贵农22(YrGN22)及Yr24等均不抗CH42;抗病遗传分析结果表明,贵农775对小麦条锈菌小种CYR32和CH42的抗性分别由一对显性核基因控制,并且为不同的小种专化抗性基因。     

水稻稻瘟病抗性基因的克隆、育种利用及稻瘟菌无毒基因研究进展

稻瘟病是世界上影响水稻(Oryza sativa)粮食生产的主要病害之一, 抗病基因的发掘与利用是抗病育种的基础和核心。随着寄主水稻和病原菌稻瘟病菌(Magnaporthe oryzae)基因组测序和基因注释的完成, 水稻和稻瘟病菌的互作体系成为研究植物与真菌互作的模式系统。该文对稻瘟病抗病基因的遗传、定位、克隆及育种利用进行概述, 并通过生物信息学分析方法, 探讨了水稻全基因组中NBS-LRR类抗病基因在水稻12条染色体上的分布情况, 同时对稻瘟病菌无毒基因的鉴定及无毒蛋白与抗病蛋白的互作进行初步分析。最后对稻瘟病抗病基因研究存在的问题进行分析并展望了未来的研究方向, 以期为水稻抗稻瘟病育种发展和抗病机制的深入理解提供参考。     

Homologues of a single resistance-gene cluster in potato confer resistance to distinct pathogens: a virus and a nematode

The isolation of the nematode-resistance gene Gpa2 in potato is described, and it is demonstrated that highly homologous resistance genes of a single resistance-gene cluster can confer resistance to distinct pathogen species. Molecular analysis of the Gpa2 locus resulted in the identification of an R-gene cluster of four highly homologous genes in a region of approximately 115 kb. At least two of these genes are active: one corresponds to the previously isolated Rx1 gene that confers resistance to potato virus X, while the other corresponds to the Gpa2 gene that confers resistance to the potato cyst nematode Globodera pallida. The proteins encoded by the Gpa2 and the Rx1 genes share an overall homology of over 88% (amino-acid identity) and belong to the leucine-zipper, nucleotide-binding site, leucine-rich repeat (LZ-NBS-LRR)-containing class of plant resistance genes. From the sequence conservation between Gpa2 and Rx1 it is clear that there is a direct evolutionary relationship between the two proteins. Sequence diversity is concentrated in the LRR region and in the C-terminus. The putative effector domains are more conserved suggesting that, at least in this case, nematode and virus resistance cascades could share common components. These findings underline the potential of protein breeding for engineering new resistance specificities against plant pathogens in vitro.     

The Arabidopsis RPS4 bacterial-resistance gene is a member of the TIR-NBS-LRR family of disease-resistance genes

Plant-disease resistance (R) genes mediate the specific recognition of invading pathogens carrying cognate avirulence (avr) determinants. RPS4 is a disease-resistance locus on chromosome 5 of Arabidopsis thaliana specifying resistance to strains of Pseudomonas syringae pv. tomato expressing avrRps4. We have isolated the RPS4 gene using a map-based cloning approach. RPS4 encodes a predicted protein of 1217 amino acids that contains an N-terminus with homology to the intracellular domains of the Drosophila Toll protein and the mammalian interleukin-1 receptor (TIR domain), a tripartite nucleotide-binding site (NBS), and leucine-rich repeats (LRR). Incomplete splicing of the RPS4 mRNA was observed, which may give rise to truncated protein products consisting mainly of the TIR and NBS domains. These features classify RPS4 as a member of the TIR-NBS-LRR R gene family founded by N, L6 and RPP5, which determine resistance to viral, fungal and oomycete pathogens, respectively. Previous work has shown that RPS4, like other Arabidopsis TIR-NBS-LRR R genes specifying resistance to oomycetes, is dependent on a functional EDS1 allele for disease-resistance signaling. The characterization of RPS4 presented here thus establishes a role for TIR-NBS-LRR R genes in resistance to bacterial pathogens, and provides evidence for the model that dependence of R genes on EDS1 is determined by R protein structure, and not by pathogen type. The cloning of RPS4 and the previous isolation of avrRps4 provide the molecular tools for a genetic and molecular dissection of the TIR-NBS-LRR R gene signaling pathway in Arabidopsis.     

Plant resistance genes: molecular and genetic organization,function and evolution

Remarkable progress is achieved now in comprehension of mechanisms that determine functioning of genes responsible for plants' phytopathogenic resistance (genes R). Cloning of great number of Monocotyledones and Dicotyledones resistance genes show that most of proteins coded by these genes have conserved amino-acid motives, which show high homology to amino-acid motives of proteins with well-designated function. Common structures for most proteins produced by genes R include nucleotide-blinding site (NBS), leucine-rich repeat (LRR), site containing homology with the cytoplasmic domains of the Drosophila Toll protein and the mammalian interleukin-1 receptor (TIR), coiled-coil structure (CC), transmembrane domain (TM), and serine/threonine proteinkinase domain (PK). They are combined within the basic classes of resistance genes proteins as follows: TIR-NBS-LRR, CC-NBS-LLRR, NBS-LRR, PK, TM-CC, LRR-TM, LRR-TM-PK. The domains of proteins produced by plant resistance genes cause specific recognition of avirulence genes products and activate signaling cascade, which gives rise to resistance reaction. Some classes of plant resistance genes probably have the same evolutionary origin as the genes that control the innate immunity of ancient animals. The evolution of plant R genes proceeds primarily by duplication and equal or unequal meiotic recombination. The research on genes R functioning besides its theoretical value is a matter of considerable practical interest for construction of plant genotypes resistant against harmful organisms. The progress in comprehension of mechanisms responsible for specificity of avirulence determinants in phytopathogenic organisms recognition makes possible the creation of artificial resistance genes.     

Insights from molecular modeling and dynamics simulation of pathogen resistance (R) protein from brinjal

Resistance (R) protein recognizes molecular signature of pathogen infection and activates downstream hypersensitive response signalling in plants. R protein works as a molecular switch for pathogen defence signalling and represent one of the largest plant gene family. Hence, understanding molecular structure and function of R proteins has been of paramount importance for plant biologists. The present study is aimed at predicting structure of R proteins signalling domains (CC-NBS) by creating a homology model, refining and optimising the model by molecular dynamics simulation and comparing ADP and ATP binding. Based on sequence similarity with proteins of known structures, CC-NBS domains were initially modelled using CED- 4 (cell death abnormality protein) and APAF-1 (apoptotic protease activating factor) as multiple templates. The final CC-NBS structural model was built and optimized by molecular dynamic simulation for 5 nanoseconds (ns). Docking of ADP and ATP at active site shows that both ligand bind specifically with same residues and with minor difference (1 Kcal/mol) in binding energy. Sharing of binding site by ADP and ATP and low difference in their binding site makes CC-NBS suitable for working as molecular switch. Furthermore, structural superimposition elucidate that CC-NBS and CARD (caspase recruitment domains) domain of CED-4 have low RMSD value of 0.9 A° Availability of 3D structural model for both CC and NBS domains will . help in getting deeper insight in these pathogen defence genes.     

大豆抗病基因同源序列的克隆与分析

已克隆的植物抗病基因序列存在一些相对保守的结构区域.利用根据核苷酸结合位点(NBS)结构域扩增所获得的大豆抗病基因同源片段为混合探针,进行大豆cDNA文库筛选.通过筛库和5'RACE-PCR扩增后,获得一全长基因KR3.KR3的长度为2353 bp,编码636个氨基酸.KR3蛋白在结构上与烟草抗花叶病毒N基因蛋白有较高的同源性,具有Toll/白细胞介素-1受体(TIR)、NBS等抗病基因的分子特征.Southern杂交显示KR3在基因组中为低拷贝;RT-PCR分析表明,该基因的表达受外源水杨酸的诱导.     

大豆抗病基因同源序列的克隆与分析

已克隆的植物抗病基因序列存在一些相对保守的结构区域。利用根据核苷酸结合位点(NBS)结构域扩增所获得的大豆抗病基因同源片段为混合探针,进行大豆cDNA文库筛选。通过筛库和5′RAcE-PcR扩增后,获得一全长基因KR3。KR3的长度为2353 bp,编码636个氨基酸。KR3蛋白在结构上与烟草抗花叶病毒N基因蛋白有较高的同源性,具有Toll／白细胞介素-1受体(TIR)、NBS等抗病基因的分了特征。Southern 杂交显KR3在基因组中为低拷贝：RT-PCR分析表明,该基因的表达受外源水杨酸的诱导。     

An EDS1 orthologue is required for N-mediated resistance against tobacco mosaic virus

In Arabidopsis, EDS1 is essential for disease resistance conferred by a structural subset of resistance (R) proteins containing a nucleotide-binding site, leucine-rich-repeats and amino-terminal similarity to animal Toll and Interleukin-1 (so-called TIR-NBS-LRR proteins). EDS1 is not required by NBS-LRR proteins that possess an amino-terminal coiled-coil motif (CC-NBS-LRR proteins). Using virus-induced gene silencing (VIGS) of a Nicotiana benthaminana EDS1 orthologue, we investigated the role of EDS1 in resistance specified by structurally distinct R genes in transgenic N. benthamiana. Resistance against tobacco mosaic virus mediated by tobacco N, a TIR-NBS-LRR protein, was EDS1-dependent. Two other R proteins, Pto (a protein kinase), and Rx (a CC-NBS-LRR protein) recognizing, respectively, a bacterial and viral pathogen did not require EDS1. These data, together with the finding that expression of N. benthamiana and Arabidopsis EDS1 mRNAs are similarly regulated, lead us to conclude that recruitment of EDS1 by TIR-NBS-LRR proteins is evolutionarily conserved between dicotyledenous plant species in resistance against bacterial, oomycete and viral pathogens. We further demonstrate that VIGS is a useful approach to dissect resistance signaling pathways in a genetically intractable plant species.