植物与病原微生物互作分子基础的研究进展

植物在与病原微生物共同进化过程中形成了复杂的免疫防卫体系。植物的先天免疫系统可大致分为两个层面。第一个层面的免疫基于细胞表面的模式识别受体对病原物相关分子模式的识别,该免疫过程被称为病原物相关分子模式触发的免疫(PAMP-triggered immunity,PTI),能帮助植物抵抗大部分病原微生物;第二个层面的免疫起始于细胞内部,主要依靠抗病基因编码的蛋白产物直接或间接识别病原微生物分泌的效应子并且激发防卫反应,来抵抗那些能够利用效应子抑制第一层面免疫的病原微生物,这一过程被称为效应子触发的免疫(Effector-triggered immunity,ETI)。这两个层面的免疫都是基于植物对"自我"及"非我"的识别,依靠MAPK级联等信号网络,将识别结果传递到细胞核内,调控相应基因的表达,做出适当的免疫应答。本文着重阐述了植物与病原微生物互作过程中不同层面的免疫反应所发生主要事件的分子基础及研究进展。     

植物与病原微生物互作分子基础的研究进展

植物在与病原微生物共同进化过程中形成了复杂的免疫防卫体系。植物的先天免疫系统可大致分为两个层面。第一个层面的免疫基于细胞表面的模式识别受体对病原物相关分子模式的识别, 该免疫过程被称为病原物相关分子模式触发的免疫(PAMP-triggered immunity, PTI), 能帮助植物抵抗大部分病原微生物; 第二个层面的免疫起始于细胞内部, 主要依靠抗病基因编码的蛋白产物直接或间接识别病原微生物分泌的效应子并且激发防卫反应, 来抵抗那些能够利用效应子抑制第一层面免疫的病原微生物, 这一过程被称为效应子触发的免疫(Effector-triggered immunity, ETI)。这两个层面的免疫都是基于植物对“自我”及“非我”的识别, 依靠MAPK级联等信号网络, 将识别结果传递到细胞核内, 调控相应基因的表达, 做出适当的免疫应答。本文着重阐述了植物与病原微生物互作过程中不同层面的免疫反应所发生主要事件的分子基础及研究进展。     

韧皮部取食昆虫诱导的植物防御反应

刺吸式昆虫与寄主植物之间具有特殊的生物互作关系。本文对刺吸式昆虫取食韧皮部诱导的植物防御反应类型、 防御物质变化、 信号途径以及植物反应转录组学研究等方面进行综述。韧皮部取食昆虫取食诱导的植物防御反应机制主要包括： (1)改变自身的营养状况; (2)产生有毒的次生化合物; (3)产生防御蛋白。防御反应与植物水杨酸、 茉莉酸、 乙烯等信号分子密切相关。研究表明, 刺吸式昆虫取食诱导的植物防御反应主要引发以水杨酸为主的信号途径, 但相关分子互作机制还有待明确。日益丰富的基因组资源和不断发展的分子生物学技术为揭示植物防御反应中信号分子的作用机制、 找出植物内生抗性的特异因子以及阐明诱导防御机制奠定了基础。了解刺吸式昆虫取食诱导的植物防御反应, 为深入理解植物-昆虫间协同进化关系提供了依据, 为害虫治理和抗虫植物的培育提供了新的思路。     

Toward understanding of rice innate immunity against Magnaporthe oryzae

The blast fungus, Magnaporthe oryzae, causes serious disease on a wide variety of grasses including rice, wheat and barley. The recognition of pathogens is an amazing ability of plants including strategies for displacing virulence effectors through the adaption of both conserved and variable pathogen elicitors. The pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) were reported as two main innate immune responses in plants, where PTI gives basal resistance and ETI confers durable resistance. The PTI consists of extracellular surface receptors that are able to recognize PAMPs. PAMPs detect microbial features such as fungal chitin that complete a vital function during the organism’s life. In contrast, ETI is mediated by intracellular receptor molecules containing nucleotide-binding (NB) and leucine rich repeat (LRR) domains that specifically recognize effector proteins produced by the pathogen. To enhance crop resistance, understanding the host resistance mechanisms against pathogen infection strategies and having a deeper knowledge of innate immunity system are essential. This review summarizes the recent advances on the molecular mechanism of innate immunity systems of rice against M. oryzae. The discussion will be centered on the latest success reported in plant–pathogen interactions and integrated defense responses in rice.     

Intracellular vs extracellular recognition of pathogens--common concepts in mammals and flies

There are common themes in innate immune defense systems across the animal and plant kingdoms. Pathogen recognition is commonly based on the identification of microbial molecular patterns by defined receptors and the subsequent activation of signaling pathways that initiate a defense response to fend off the invading microorganism. The existence of mammalian Toll-like receptors (TLRs) and the recent identification of two mammalian nucleotide-binding site leucine-rich repeat (NBS-LRR) proteins (NOD1 and NOD2) as intracellular sensors of bacterial products bring new insights into the possibility of extracellular versus intracellular pathogen recognition and signal transduction depending on the nature of the infection. The homology between TLRs and the Toll system in Drosophila suggests that conserved defense mechanisms are likely to be shared by diverse organisms.     

Lectin-mediated resistance impairs plant virus infection at the cellular level

Plants possess a multilayered defense response, known as plant innate immunity, to infection by a wide variety of pathogens. Lectins, sugar binding proteins, play essential roles in the innate immunity of animal cells, but the role of lectins in plant defense is not clear. This study analyzed the resistance of certain Arabidopsis thaliana ecotypes to a potexvirus, plantago asiatica mosaic virus (PlAMV). Map-based positional cloning revealed that the lectin gene JACALIN-TYPE LECTIN REQUIRED FOR POTEXVIRUS RESISTANCE1 (JAX1) is responsible for the resistance. JAX1-mediated resistance did not show the properties of conventional resistance (R) protein-mediated resistance and was independent of plant defense hormone signaling. Heterologous expression of JAX1 in Nicotiana benthamiana showed that JAX1 interferes with infection by other tested potexviruses but not with plant viruses from different genera, indicating the broad but specific resistance to potexviruses conferred by JAX1. In contrast with the lectin gene RESTRICTED TEV MOVEMENT1, which inhibits the systemic movement of potyviruses, which are distantly related to potexviruses, JAX1 impairs the accumulation of PlAMV RNA at the cellular level. The existence of lectin genes that show a variety of levels of virus resistance, their targets, and their properties, which are distinct from those of known R genes, suggests the generality of lectin-mediated resistance in plant innate immunity.     

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．     

Innate immunity in plants and animals: emerging parallels between the recognition of general elicitors and pathogen-associated molecular patterns

Recent findings have highlighted remarkable similarities in the innate pathogen defense systems of plants, animals and insects. Pathogen-associated molecular patterns (PAMP) that are similar to those activating innate immune responses in animals have been shown to mediate the activation of plant defense. Moreover, recognition complexes that are structurally related to animal PAMP receptors are now being discovered in plants, suggesting a common evolutionary origin of pathogen defense systems in higher eukaryotes.     

Receptor-like kinases and receptor-like proteins: keys to pathogen recognition and defense signaling in plant innate immunity

Plants have evolved multiple layers of defense against various pathogens in the environment. Receptor-like kinases/proteins (RLKs/RLPs) are on the front lines of the battle between plants and pathogens since they are present at the plasma membrane and perceive signature molecules from either the invading pathogen or damaged plant tissue. With a few notable exceptions, most RLKs/RLPs are positive regulators of plant innate immunity. In this review, we summarize recently discovered RLKs/RLPs that are involved in plant defense responses against various classes of pathogens.We also describe what is currently known about the mechanisms of RLK-mediated initiation of signaling via protein-protein interactions and phosphorylation.     

Role of pathogen's effectors in understanding host-pathogen interaction

Pathogens can pose challenges to plant growth and development at various stages of their life cycle. Two interconnected defense strategies prevent the growth of pathogens in plants, i.e., molecular patterns triggered immunity (PTI) and pathogenic effector-triggered immunity (ETI) that often provides resistance when PTI no longer functions as a result of pathogenic effectors. Plants may trigger an ETI defense response by directly or indirectly detecting pathogen effectors via their resistance proteins. A typical resistance protein is a nucleotide-binding receptor with leucine-rich sequences (NLRs) that undergo structural changes as they recognize their effectors and form associations with other NLRs. As a result of dimerization or oligomerization, downstream components activate “helper” NLRs, resulting in a response to ETI. It was thought that ETI is highly dependent on PTI. However, recent studies have found that ETI and PTI have symbiotic crosstalk, and both work together to create a robust system of plant defense. In this article, we have summarized the recent advances in understanding the plant's early immune response, its components, and how they cooperate in innate defense mechanisms. Moreover, we have provided the current perspective on engineering strategies for crop protection based on up-to-date knowledge.     

System of innate immunity in plants

The review deals with the mechanisms of innate immunity in plants focusing on families of pattern-recognition receptors and incorporates recent data on complete sequencing of several plant genomes. Plant immune response involves several families of receptors, both membrane-bound and cytoplasmic ones, containing conservative leucine-rich repeats. The lack of adaptive immunity and the associated rearrangements in the immune receptor genes in plants is partly counterbalanced by genetically encoded mechanisms of specific immunity to particular pathogens. There is a certain similarity between intracellular signal transduction and effector mechanisms in plant and animal innate immune systems, although the latter are considerably more complex.     

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.     

水稻抗稻瘟病基因资源与分子育种策略

稻瘟病是水稻主要病害之一。利用抗病品种是防治稻瘟病最经济、有效和安全的措施。近年来,随着植物先天免疫机制、抗病分子生物学以及水稻和稻瘟菌基因组学研究的不断深入,一系列参与病原菌识别和防卫信号传导与应答,以及外源抗菌蛋白、病原菌激发子等抗病相关基因陆续被鉴定和克隆,为提高水稻抗稻瘟病能力提供了一些新的基因资源、育种策略和技术。本文概述了国内外近年来克隆的主要抗稻瘟病基因资源及其在分子育种研究中应用的进展,提出了通过转基因手段整合不同防卫反应关键调控基因的抗稻瘟病聚合育种策略。     

Plant pathogenic bacterial type III effectors subdue host responses

Like animals, plants sense bacterial pathogens through surface-localized pattern recognition receptors (PRRs) and intracellular nucleotide-binding leucine-rich repeat proteins (NB-LRR) and trigger defense responses. Many plant-pathogenic bacteria secrete a large repertoire of effector proteins into host cells to modulate host responses, enabling successful infection and multiplication in plants. A number of these effector proteins target plant innate immunity signaling pathways, while others induce specific host genes to enhance plant susceptibility. Substantial progress has been made in the past two years concerning biochemical function of effectors and their host targets. These advances provide new insights into regulatory mechanisms of plant immunity and host-pathogen co-evolution.     

The worm has turned--microbial virulence modeled in Caenorhabditis elegans

The nematode Caenorhabditis elegans is emerging as a facile and economical model host for the study of evolutionarily conserved mechanisms of microbial pathogenesis and innate immunity. A rapidly growing number of human and animal microbial pathogens have been shown to injure and kill nematodes. In many cases, microbial genes known to be important for full virulence in mammalian models have been shown to be similarly required for maximum pathogenicity in nematodes. C. elegans has been used in mutation-based screening systems to identify novel virulence-related microbial genes and immune-related host genes, many of which have been validated in mammalian models of disease. C. elegans-based pathogenesis systems hold the potential to simultaneously explore the molecular genetic determinants of both pathogen virulence and host defense.     

R proteins as fundamentals of plant innate immunity

Plants are attacked by a wide spectrum of pathogens, being the targets of viruses, bacteria, fungi, protozoa, nematodes and insects. Over the course of their evolution, plants have developed numerous defense mechanisms including the chemical and physical barriers that are constitutive elements of plant cell responses locally and/or systemically. However, the modern approach in plant sciences focuses on the evolution and role of plant protein receptors corresponding to specific pathogen effectors. The recognition of an invader’s molecules could be in most cases a prerequisite sine qua non for plant survival. Although the predicted three-dimensional structure of plant resistance proteins (R) is based on research on their animal homologs, advanced technologies in molecular biology and bioinformatics tools enable the investigation or prediction of interaction mechanisms for specific receptors with pathogen effectors. Most of the identified R proteins belong to the NBS-LRR family. The presence of other domains (including the TIR domain) apart from NBS and LRR is fundamental for the classification of R proteins into subclasses. Recently discovered additional domains (e.g. WRKY) of R proteins allowed the examination of their localization in plant cells and the role they play in signal transduction during the plant resistance response to biotic stress factors. This review focuses on the current state of knowledge about the NBS-LRR family of plant R proteins: their structure, function and evolution, and the role they play in plant innate immunity.     

Plant latex and other exudates as plant defense systems: roles of various defense chemicals and proteins contained therein

Plant latex and other exudates are saps that are exuded from the points of plant damage caused either mechanically or by insect herbivory. Although many (ca. 10%) of plant species exude latex or exudates, and although the defensive roles of plant latex against herbivorous insects have long been suggested by several studies, the detailed roles and functions of various latex ingredients, proteins and chemicals, in anti-herbivore plant defenses have not been well documented despite the wide occurrence of latex in the plant kingdom. Recently, however, substantial progress has been made. Several latex proteins, including cysteine proteases and chitin-related proteins, have been shown to play important defensive roles against insect herbivory. In the mulberry (Morus spp.)-silkworm (Bombyx mori) interaction, an old and well-known model system of plant-insect interaction, plant latex and its ingredients - sugar-mimic alkaloids and defense protein MLX56 - are found to play key roles. Complicated molecular interactions between Apocynaceae species and its specialist herbivores, in which cardenolides and defense proteins in latex play key roles, are becoming more and more evident. Emerging observations suggested that plant latex, analogous to animal venom, is a treasury of useful defense proteins and chemicals that has evolved through interspecific interactions. On the other hand, specialist herbivores developed sophisticated adaptations, either molecular, physiological, or behavioral, against latex-borne defenses. The existence of various adaptations in specialist herbivores itself is evidence that latex and its ingredients function as defenses at least against generalists. Here, we review molecular and structural mechanisms, ecological roles, and evolutionary aspects of plant latex as a general defense against insect herbivory and we discuss, from recent studies, the unique characteristics of latex-borne defense systems as transport systems of defense substances are discussed based on recent studies.