植物非寄主抗性

本综述从植物－微生物互作出发,对决定植物非寄主抗性的遗传基因和信号传导途径进行了分析,提出了利用植物非寄主抗性的可能途径。     

植物非寄主抗性研究进展

非寄主抗性是植物对大多数病原微生物最普遍的抗病形式, 由于它具有广谱持久的特性, 因此在农业上有着广阔的应用前景。尽管近年来对植物抗病的分子机理研究取得了很大进展, 但对植物非寄主抗性分子机制仍不十分了解。文章对目前研究的非寄主抗性产生分子机理、植物与病原物的互作系统、PEN1编码的SNARE蛋白参与非寄主抗性、非寄主抗性研究所面临的困难以及今后的发展前景进行了概述。     

大豆蚜在寄主与非寄主植物上的口针刺吸行为

用EPG记录法记录了大豆蚜Aphis glycines Matsunra在寄主和非寄主植物上的口针刺吸行为。结果表明,大豆蚜在寄主大豆植物的韧皮部取食时间长,而在非寄主棉花、黄瓜和丝瓜植物韧皮部取食时间甚短或根本未取食;非寄主植物内部对大豆蚜的侵害存在抗性,影响取食的因素和其所在部位因非寄主植物种类的不同而不同。     

植物抗病反应的信号传导网络

植物由抗病基因介导的防卫过程存在一系列生理生化和分子生物学反应,这些反应从病原菌侵染点开始的超敏反应(HR)并延伸到远处组织的系统抗性或获得性抗性(SAR),受制于一种信号传导网络的调控。这个信号系统由抗病蛋白和病原菌非毒性蛋白在一种配体-受体的互作模式下激发,并由信号分子H2O2,NO和系统信号分子SA,JA和乙烯和通过关键调控基因传递和放大,最终诱导一系列防卫反应基因的表达和代谢的变化而产生抗性。植物防卫信号的产生有类似于动物免疫系统因子的介导,并可由非寄主病原菌或诱导子诱发。这些信号途径所产生的广谱抗性为植物抗病基因工程的应用奠定了基础。     

植物抗病反应的信号传导网络

植物由抗病基因介导的防卫过程存在一系列生理生化和分子生物学反应,这些反应从病原菌侵染点开始的超敏反应（HR）并延伸到远处组织的系统抗性或获得性抗性（SAR）,受制于一种信号传导网络的调控,这个信号系统由抗病蛋白和病原菌非毒性蛋白在一种配体-受体的互作模式下激发,并由信号分子H2O2,NO和系统信号分子SA,JA和乙烯和通过关键调控基因传递和放大,最终诱导一系列防卫反应基因的表达和代谢的变化而产生抗性。植物防卫信号的产生有类似于动物免疫系统因子的介导,并可由非寄主病原菌或诱导子诱发,这些信号途径所产生的广谱抗性为植物抗病基因工程的应用奠定了基础。     

生防菌诱导植物系统抗性及其生化和细胞学机制

生防菌通常可利用竞争、抗生、寄生和交叉保护等直接的拮抗机制抑制植物病害;同时某些生防菌还能促进植物生长,诱导植物对真菌、细菌和病毒引起的病害乃至对线虫和昆虫为害的抗性,称为诱导系统抗性(ISR).ISR具有非特异性、广谱性和系统性,其在表型上与病原菌侵染激发的系统获得抗性(SAR)相似,具有同样的效率;但在寄主植物上不发生过敏性坏死反应(HR),无可见症状,为发展和改善更加安全而环境友好的植物保护策略开辟了新的思路.本文总结了生防真菌和细菌诱导系统抗性及其激发子和信号转导途径等方面的研究进展,重点阐述了寄主防御反应的生化和细胞学机制,并对ISR在植物病害生物防治中的应用前景进行了展望.     

粳稻品种中丹2号抗稻瘟病基因的残效

Nelson认为,在病原菌寄生物与植物寄主的共同 进化过程中,寄生物对某种寄主抗性的克服并不是完 全的。也就是说,某个抗病基因即使丧失抗性,但对该 菌系仍有一定残效抗性,使寄主表现不太严重的感病。 以前,仅有几例这方面的报道。我们在对水稻稻瘟病 抗病基因的研究中,也发现这一现象。     

寄主监控昆虫唾液蛋白平衡植物抗性与生长发育

作物生产常遭受各类虫害威胁。揭示昆虫与寄主之间的互作机制,对害虫的绿色防治具有重要意义。武汉大学何光存团队鉴定了褐飞虱(BPH)唾液蛋白BISP。在易感品种中, BISP靶向OsRLCK185并抑制其介导的基础防御。在携带褐飞虱抗性基因Bph14的水稻(Oryza sativa)品种中,BPH14直接结合BISP并激活寄主的免疫反应,但会抑制水稻的生长。BISP-BPH14与自噬装载受体OsNBR1结合,通过自噬途径降解BISP,下调水稻对BPH的抗性,恢复植株正常生长。该研究鉴定到首个被植物免疫受体感知的昆虫唾液蛋白,揭示了寄主通过感知并调节昆虫效应蛋白水平来平衡水稻抗性与生长发育的分子机制,为培育高产水稻抗虫品种提供了新思路。     

昆虫对植物抗虫性的诱导

植物的抗虫性主要表现为受遗传因素控制的遗传抗性和受环境因素控制的生态抗性两个方面。植物的抗性主要由遗传因素决定,但其抗性表达和抗虫幅度又受到环境因子的影响。环境因子可改变植物的生理状态和理化性质,使植物不合适作为某种昆虫的寄主,从而提高了植物的抗性水平。植食性昆虫对植物抗虫性的诱导是环境影响抗性表达的一个重要方面,它是植物对取食者的一种重要的防御策略,同时也是植物与植食者协同进化的结果,进一步了解和充分发挥诱导抗性的作用,对抗虫有种工作和害虫的综合治理都有指导意义。三植食性昆虫对植物抗虫性的诱导…     

大豆疫霉与大豆互作中的识别与反识别

大豆疫霉引起的大豆疫病是大豆生产上的毁灭性病害。深入了解大豆疫霉与寄主在分子层面的互作机制是解析病原菌致病机理、针对性地制定防治措施的必要前提。目前研究表明,植物通过两个层面的识别机制来启动防卫反应,而能否正确识别"非我"分子则是植物开启免疫系统的关键。而对于病原菌,则采用多种分子策略来极力逃避寄主的识别机制,分泌效应分子协同抑制寄主免疫反应。本文综述了一系列大豆抗病基因介导的小种专化抗性丧失的原因,以及大豆疫霉效应分子逃避和破坏寄主免疫反应的分子策略,并讨论了基于这些分子互作机制应用于筛选新型抗病资源和精确育种的可能性。     

Nonhost resistance: how much do we know?

Nonhost disease resistance is the most common form of disease resistance exhibited by plants against the majority of potentially pathogenic microorganisms. Recently, several components of nonhost disease resistance have been identified. Nonhost resistance exhibited against bacteria, fungi and oomycetes can be of two types. Type I nonhost resistance does not produce any visible symptoms whereas type II nonhost resistance results in a rapid hypersensitive response with cell death. Strong similarities exist between nonhost and gene-for-gene resistance responses but it is still not clear if the same mechanism is involved in producing these resistance responses.     

Glycolate oxidase modulates reactive oxygen species-mediated signal transduction during nonhost resistance in Nicotiana benthamiana and Arabidopsis

In contrast to gene-for-gene disease resistance, nonhost resistance governs defense responses to a broad range of potential pathogen species. To identify specific genes involved in the signal transduction cascade associated with nonhost disease resistance, we used a virus-induced gene-silencing screen in Nicotiana benthamiana, and identified the peroxisomal enzyme glycolate oxidase (GOX) as an essential component of nonhost resistance. GOX-silenced N. benthamiana and Arabidopsis thaliana GOX T-DNA insertion mutants are compromised for nonhost resistance. Moreover, Arabidopsis gox mutants have lower H(2)O(2) accumulation, reduced callose deposition, and reduced electrolyte leakage upon inoculation with hypersensitive response-causing nonhost pathogens. Arabidopsis gox mutants were not affected in NADPH oxidase activity, and silencing of a gene encoding NADPH oxidase (Respiratory burst oxidase homolog) in the gox mutants did not further increase susceptibility to nonhost pathogens, suggesting that GOX functions independently from NADPH oxidase. In the two gox mutants examined (haox2 and gox3), the expression of several defense-related genes upon nonhost pathogen inoculation was decreased compared with wild-type plants. Here we show that GOX is an alternative source for the production of H(2)O(2) during both gene-for-gene and nonhost resistance responses.     

Resistance to oomycetes: a general role for the hypersensitive response?

Oomycete plant pathogens, such as Phytophthora, downy mildews and Pythium, have devastating disease effects on numerous crop and ornamental plants. Various types of genetic resistance to oomycetes occur in plants, and can be determined at the subspecific or varietal level (race or cultivar-specific resistance), or at the species or genus level (nonhost resistance). In addition, resistance might be a quantitative phenotype (partial resistance). Resistance reactions are often associated with the hypersensitive response – a programed cell death pathway. Recent advances in the genetic, biochemical and cytological characterization of disease resistance suggests that the hypersensitive response is associated with all forms of resistance to Phytophthora and downy mildews. Identification of the resistance genes involved in nonhost and partial resistance to oomycetes remains an important challenge.     

Nonhost resistance to Phytophthora: novel prospects for a classical problem.

Members of the oomycete genus Phytophthora are the most devastating pathogens of dicot plants. Recent developments in the study of these organisms have led to improved understanding of their phylogenetic relationships and trends in their evolution. Molecular analyses of nonhost (species-level) resistance offer exciting prospects for disease management. A model that evokes a complex interplay of several layers of specific resistance, mediated by a set of ancient broad-spectrum R-gene loci, is sufficient to explain existing cellular and molecular data on nonhost resistance to Phytophthora.     

Arabidopsis NHO1 is required for general resistance against Pseudomonas bacteria

Nonhost interactions are prevalent between plants and specialized phytopathogens. Although it has great potential for providing crop plants with durable resistance, nonhost resistance is poorly understood. Here, we show that nonhost resistance is controlled, at least in part, by general resistance. Arabidopsis plants are resistant to the nonhost pathogen Pseudomonas syringae pv phaseolicola NPS3121 and completely arrest bacterial multiplication in the plant. Ten Arabidopsis mutants were isolated that were compromised in nonhost (nho) resistance to P. s. phaseolicola. Among these, nho1 is caused by a single recessive mutation that defines a novel gene. nho1 is defective in nonspecific resistance to Pseudomonas bacteria, because it also supported the growth of P. s. tabaci and P. fluorescens bacteria, both of which are nonpathogenic on Arabidopsis. In addition, the nho1 mutation also compromised resistance mediated by RPS2, RPS4, RPS5, and RPM1. Interestingly, the nho1 mutation had no effect on the growth of the virulent bacteria P. s. maculicola ES4326 and P. s. tomato DC3000, but it partially restored the in planta growth of the DC3000 hrpS(-) mutant bacteria. Thus, the virulent bacteria appear to evade or suppress NHO1-mediated resistance by means of an Hrp-dependent virulence mechanism.     

Pseudomonas Type III effector AvrPto suppresses the programmed cell death induced by two nonhost pathogens in Nicotiana benthamiana and tomato

Many gram-negative bacterial pathogens rely on a type III secretion system to deliver a number of effector proteins into the host cell. Though a number of these effectors have been shown to contribute to bacterial pathogenicity, their functions remain elusive. Here we report that AvrPto, an effector known for its ability to interact with Pto and induce Pto-mediated disease resistance, inhibited the hypersensitive response (HR) induced by nonhost pathogen interactions. Pseudomonas syringae pv. tomato T1 causes an HR-like cell death on Nicotiana benthamiana. This rapid cell death was delayed significantly in plants inoculated with P. syringae pv. tomato expressing avrPto. In addition, P. syringae pv. tabaci expressing avrPto suppressed nonhost HR on tomato prf3 and ptoS lines. Transient expression of avrPto in both N. benthamiana and tomato prf3 plants also was able to suppress nonhost HR. Interestingly, AvrPto failed to suppress cell death caused by other elicitors and nonhost pathogens. AvrPto also failed to suppress cell death caused by certain gene-for-gene disease resistance interactions. Experiments with avrPto mutants revealed several residues important for the suppression effects. AvrPto mutants G2A, G99V, P146L, and a 12-amino-acid C-terminal deletion mutant partially lost the suppression ability, whereas S94P and 196T enhanced suppression of cell death in N. benthamiana. These results, together with other discoveries, demonstrated that suppression of host-programmed cell death may serve as one of the strategies bacterial pathoens use for successful invasion.     

Organ identity and environmental conditions determine the effectiveness of nonhost resistance in the interaction between Arabidopsis thaliana and Magnaporthe oryzae

Mechanisms leading to nonhost resistance of plants against nonadapted pathogens are thought to have great potential for the future management of agriculturally important diseases. In this article, we report an investigation of nonhost resistance motivated by the advantages of studying an interaction between two model organisms, namely Arabidopsis thaliana and Magnaporthe oryzae. During the course of our studies, however, we discovered an unexpected plasticity in the responses of Arabidopsis against this ostensibly nonhost pathogen. Thus, we elucidated that certain experimental conditions, such as the growth of plants under long days at constantly high humidity and the use of high inoculum concentrations of M. oryzae conidia, forced the interaction in leaves of some Arabidopsis ecotypes towards increased compatibility. However, sporulation was never observed. Furthermore, we observed that roots were generally susceptible to M. oryzae, whereas leaves, stems and hypocotyls were not infected. It must be concluded, therefore, that Arabidopsis roots lack an effective defence repertoire against M. oryzae, whereas its leaves possess such nonhost defence mechanisms. In summary, our findings point to organ-specific determinants and environmental conditions influencing the effectiveness of nonhost resistance in plants.     

High diversity of genes for nonhost resistance of barley to heterologous rust fungi

Inheritance studies on the nonhost resistance of plants would normally require interspecific crosses that suffer from sterility and abnormal segregation. Therefore, we developed the barley-Puccinia rust model system to study, using forward genetics, the specificity, number, and diversity of genes involved in nonhost resistance. We developed two mapping populations by crossing the line SusPtrit, with exceptional susceptibility to heterologous rust species, with the immune barley cultivars Vada and Cebada Capa. These two mapping populations along with the Oregon Wolfe Barley population, which showed unexpected segregation for resistance to heterologous rusts, were phenotyped with four heterologous rust fungal species. Positions of QTL conferring nonhost resistance in the three mapping populations were compared using an integrated consensus map. The results confirmed that nonhost resistance in barley to heterologous rust species is controlled by QTL with different and overlapping specificities and by an occasional contribution of an R-gene for hypersensitivity. In each population, different sets of loci were implicated in resistance. Few genes were common between the populations, suggesting a high diversity of genes conferring nonhost resistance to heterologous pathogens. These loci were significantly associated with QTL for partial resistance to the pathogen Puccinia hordei and with defense-related genes.