植食性昆虫唾液效应子和激发子的研究进展

植食性昆虫与寄主植物通过协同进化形成了复杂的防御和反防御机制.本文系统综述了昆虫唾液效应子和激发子在植物与昆虫互作中的作用及机理.昆虫取食中释放的唾液激发子被植物识别而激活植物早期免疫反应,昆虫也能从口腔分泌效应子到植物体内抑制免疫;抗性植物则利用抗性(R)蛋白识别昆虫无毒效应子,启动效应子诱导的免疫反应,而昆虫又进化...     

一氧化氮与激发子诱导的植物抗病防卫反应

来源于真菌或植物细胞壁的激发子可以诱导植物的抗性反应。一系列的信号分子,如一氧化氮、活性氧、茉莉酸、水杨酸、乙烯等都参与了激发子诱导的植物抗性反应。它们在介导激发子刺激诱发胞内抗性反应的过程中起着重要的作用。本文介绍了激发子的种类,并简述了激发了受体以及植物细胞对激发子刺激的感受与传递;重点介绍了一氧化氮在激发子诱导植物抗性反应过程中的作用,以及它与其他信号分子之间相互关系的研究进展。     

The Myriad Plant Responses to Herbivores

Abstract Plant responses to herbivores are complex. Genes activated on herbivore attack are strongly correlated with the mode of herbivore feeding and the degree of tissue damage at the feeding site. Phloem-feeding whiteflies and aphids that produce little injury to plant foliage are perceived as pathogens and activate the salicylic acid (SA)-dependent and jasmonic acid (JA)/ethylene-dependent signaling pathways. Differential expression of plant genes in response to closely related insect species suggest that some elicitors generated by phloem-feeding insects are species-specific and are dependent on the herbivore's developmental stage. Other elicitors for defense-gene activation are likely to be more ubiquitous. Analogies to the pathogen-incompatible reactions are found. Chewing insects such as caterpillars and beetles and cell-content feeders such as mites and thrips cause more extensive tissue damage and activate wound-signaling pathways. Herbivore feeding is not equivalent to mechanical wounding. Wound responses are a part of the induced responses that accompany herbivore feeding. Herbivores induce direct defenses that interfere with herbivore feeding, growth and development, fecundity, and fertility. In addition, herbivores induce an array of volatiles that creates an indirect mechanism of defense. Volatile blends provide specific cues to attract herbivore parasites and predators to infested plants. The nature of the elicitors for volatile production is discussed.     

Signals Regulating Multiple Responses to Wounding and Herbivores

Damage inflicted by herbivore feeding necessitates multiple defense strategies in plants. The wound site must be sealed and defense responses mounted against the herbivore itself and against invading opportunistic pathogens. These defenses are controlled both in time and space by highly complex regulatory networks that themselves are modulated by interactions with other signaling pathways. In this review, we describe the signaling events that occur in individual wounded leaves, in systemic unwounded regions of the plant, and between the plant, and other organisms, and attempt to place these events in the context of a coordinated system. Key signals that are discussed include ion fluxes, active oxygen species, protein phosphorylation cascades, the plant hormones jasmonic acid, ethylene, abscisic acid and salicylic acid, peptide signals, glycans, volatile chemicals, and physical signals such as hydraulic and electrical signals. Themes that emerge after consideration of the published data are that glycans and peptide elicitors are likely primary triggers of wound-induced defense responses and that they function through the action of jasmonic acid, a central mediator of defense gene expression, whose effect is modulated by ethylene. In the field, wound signaling pathways are significantly impacted on by other stress response pathways, including pathogen responses that often operate through potentially antagonistic signals such as salicylic acid. However, gross generalisations are not possible because some wound and pathogen responses operate through common jasmonate- and ethylene-dependent pathways. Understanding the ways in which local and systemic wound signaling pathways are coordinated individually and in the context of the plants wider environment is a key challenge in the application of this science to crop-protection strategies.     

The Plant-Stress Metabolites,Hexanoic Aacid and Melatonin,Are Potential “Vaccines” for Plant Health Promotion

A plethora of compounds stimulate protective mechanisms in plants against microbial pathogens and abiotic stresses. Some defense activators are synthetic compounds and trigger responses only in certain protective pathways, such as activation of defenses under regulation by the plant regulator, salicylic acid (SA). This review discusses the potential of naturally occurring plant metabolites as primers for defense responses in the plant. The production of the metabolites, hexanoic acid and melatonin, in plants means they are consumed when plants are eaten as foods. Both metabolites prime stronger and more rapid activation of plant defense upon subsequent stress. Because these metabolites trigger protective measures in the plant they can be considered as “vaccines” to promote plant vigor. Hexanoic acid and melatonin instigate systemic changes in plant metabolism associated with both of the major defense pathways, those regulated by SA- and jasmonic acid (JA). These two pathways are well studied because of their induction by different microbial triggers: necrosis-causing microbial pathogens induce the SA pathway whereas colonization by beneficial microbes stimulates the JA pathway. The plant’s responses to the two metabolites, however, are not identical with a major difference being a characterized growth response with melatonin but not hexanoic acid. As primers for plant defense, hexanoic acid and melatonin have the potential to be successfully integrated into vaccination-like strategies to protect plants against diseases and abiotic stresses that do not involve man-made chemicals.     

How do plants “notice” attack by herbivorous arthropods?

Precise and deep comprehension of plant responses to herbivorous arthropods requires detailed knowledge of how a plant “notices” the attack. Herbivore attack is not restricted to plant wounding by feeding, but instead different phases of attack that elicit a plant response need to be distinguished: touch, oviposition and feeding. Touch, secretions released with eggs and regurgitate delivered during feeding may act in concert as elicitors of plant defence. Here, we discuss the current knowledge of what a plant “notices” during the different phases of herbivore attack and how it responds at the molecular, physiological and ecological level. Understanding the mechanisms of plant responses to the different phases of herbivore attack will be a key challenge in unravelling the complex communication pathways between plants and herbivores.     

Responses of Arabidopsis thaliana to challenge by Pseudomonas syringae

Plants are continually exposed to a variety of potentially pathogenic microbes, and the interactions between plants and pathogenic invaders determine the outcome, disease or disease resistance. To defend themselves, plants have developed a sophisticated immune system. Unlike animals, however, they do not have specialized immune cells and, thus all plant cells appear to have the innate ability to recognize pathogens and turn on an appropriate defense response. Using genetic, genomic and biochemical methods, tremendous advances have been made in understanding how plants recognize pathogens and mount effective defenses. The primary immune response is induced by microbe-associated molecular patterns (MAMPs). MAMP receptors recognize the presence of probable pathogens and evoke defense. In the co-evolution of plant-microbe interactions, pathogens gained the ability to make and deliver effector proteins to suppress MAMP-induced defense responses. In response to effector proteins, plants acquired R-proteins to directly or indirectly monitor the presence of effector proteins and activate an effective defense response. In this review we will describe and discuss the plant immune responses induced by two types of elicitors, PAMPs and effector proteins.     

Physiological function and ecological aspects of fatty acid-amino acid conjugates in insects†

In tritrophic interactions, plants recognize herbivore-produced elicitors and release a blend of volatile compounds (VOCs), which work as chemical cues for parasitoids or predators to locate their hosts. From detection of elicitors to VOC emissions, plants utilize sophisticated systems that resemble the plant–microbe interaction system. Fatty acid–amino acid conjugates (FACs), a class of insect elicitors, resemble compounds synthesized by microbes in nature. Recent evidence suggests that the recognition of insect elicitors by an ancestral microbe-associated defense system may be the origin of tritrophic interactions mediated by FACs. Here we discuss our findings in light of how plants have customized this defense to be effective against insect herbivores, and how some insects have successfully adapted to these defenses.     

昆虫取食诱导的植物防御反应

植物被昆虫取食后可产生直接防御或间接防御。直接防御通过增加有毒的次生代谢产物或防御蛋白对昆虫生理代谢产生不利的影响,但对植物的消耗较大。间接防御通过释放挥发性化合物吸引天敌昆虫,并以此控制植食性昆虫。特异性的昆虫激发子(insect specific elicitors)能够诱导挥发性化合物的释放。多种信号途径参与昆虫取食诱导的植物防御反应,它们之间的相互作用协同或拮抗。了解昆虫取食诱导的植物防御反应,对于害虫综合治理策略的完善具有重要的意义。     

Biochemical aspects of plant interactions with parasite nematodes. (A review)

The review summarizes reports on molecular aspects of interactions of phytoparasitic nematodes with plant hosts. Data on the secrets of nematodes affecting plants (elicitors, toxins, products of parasitism genes, etc.) are analyzed and information flow pathways comprising all elements of the plant-parasite interaction (from elicitors to defense responses of plant cells), described. Emphasis is placed on the mechanisms whereby plants are protected from nematode invasion (hypesensitivity reactions, apoptosis, phytoalexins, proteinase inhibitors, PR-proteins, etc.). Consideration is given to genetic aspects of plant-parasite relationships. Promising practical approaches to defending plants from phytoparasitic nematodes, developed based on the results of studies of molecular mechanisms of plant-parasite interactions are provided in conclusion.     

Salivary signals of European corn borer induce indirect defenses in tomato

Plants can recognize the insect elicitors and activate its defense mechanisms. European Corn Borer (ECB; Ostrinia nubilalis) saliva, produced from the labial salivary glands and released through the spinneret, is responsible for inducing direct defenses in host plants. Glucose oxidase (GOX) present in the ECB saliva induced direct defenses in tomato. By contrast, GOX activity in ECB saliva was insufficient to trigger defenses in maize, suggesting that host-specific salivary elicitors are responsible for inducing direct defenses in host plants. Our current study further examined whether ECB saliva can trigger indirect defenses in tomato. Relative expression levels of TERPENE SYNTHASE5 (TPS5) and HYDROPEROXIDE LYASE (HPL), marker for indirect defenses in host plants, were monitored. Quantitative real-time PCR analysis revealed that ECB saliva can induce the expression of TPS5 and HPL, suggesting that salivary signals can induce indirect defenses in addition to the direct defenses. Further experiments are required to identify different ECB elicitors that are responsible for inducing direct and indirect defenses in host plants.     

Chitooligosaccharide sensing and downstream signaling: contrasted outcomes in pathogenic and beneficial plant–microbe interactions

In plants, short chitin oligosaccharides and chitosan fragments (collectively referred to as chitooligosaccharides) are well-known elicitors that trigger defense gene expression, synthesis of antimicrobial compounds, and cell wall strengthening. Recent findings have shed new light on chitin-sensing mechanisms and downstream activation of intracellular signaling networks that mediate plant defense responses. Interestingly, chitin receptors possess several lysin motif domains that are also found in several legume Nod factor receptors. Nod factors are chitin-related molecules produced by nitrogen-fixing rhizobia to induce root nodulation. The fact that chitin and Nod factor receptors share structural similarity suggests an evolutionary conserved relationship between mechanisms enabling recognition of both deleterious and beneficial microorganisms. Here, we will present an update on molecular events involved in chitooligosaccharide sensing and downstream signaling pathways in plants and will discuss how structurally related signals may lead to such contrasted outcomes during plant–microbe interactions.     

Riboflavin-induced Priming for Pathogen Defense in Arabidopsis thaliana

Riboflavin (vitamin B2) participates in a variety of redox processes that affect plant defense responses. Previously we have shown that riboflavin induces pathogen resistance in the absence of hypersensitive cell death (HCD) in plants. Herein, we report that riboflavin induces priming of defense responses in Arabidopsis thaliana toward infection by virulent Pseudomonas syringae pv. Tomato DC3000 (Pst). Induced resistance was mechanistically connected with the expression of defense response genes and cellular defense events, including H2O2 burst, HCD, and callose deposition in the plant. Riboflavin treatment and inoculation of plants with Pst were neither active but both synergized to induce defense responses. The priming process needed NPR1 (essential regulator of systemic acquired resistance) and maintenance of H2O2 burst but was independent of salicylic acid, jasmonic acid, ethylene, and abscisic acid. Our results suggest that the role of riboflavin in priming defenses is subject to a signaling process distinct from the known pathways of hormone signal transduction.     

Innate immunity in plants: a continuum of layered defenses

Plant responses to pathogenic invaders result from recognition of nonself elicitors. Host surveillance proteins activate distinct signaling pathways that induce partially overlapping defensive responses. Pathogen virulence is promoted by inhibition of these pathways. This evolutionary struggle has produced plant immune systems that rely on a continuum of layered defenses.     

Biochemical Aspects of Plant Interactions with Phytoparasitic Nematodes: A Review

The review summarizes reports on molecular aspects of interactions of phytoparasitic nematodes with plant hosts. Data on nematode secretions affecting plants (elicitors, toxins, products of parasitism genes, etc.) are analyzed and information flow pathways comprising all elements of the plant–parasite interaction (from elicitors to defense responses of plant cells) are described. Emphasis is placed on the mechanisms whereby plants are protected from nematode invasion (hypersensitivity reactions, apoptosis, phytoalexins, proteinase inhibitors, PR proteins, etc.). Consideration is given to genetic aspects of plant–parasite relationships. Promising practical approaches to defending plants from phytoparasitic nematodes developed based on the results of studies of molecular mechanisms of plant–parasite interactions are presented in the conclusion.     

Phytohormonal signaling in plant responses to aphid feeding

Aphid feeding induces various defense signaling mechanisms in plants. The recognition of feeding activities by plants occurs through the use of transmembrane pattern recognition receptors (PRRS) or, acting largely inside the cell, polymorphic nucleotide-binding leucine-rich-repeat (NB-LRR) protein products, encoded by most R genes. Activation may induce defensive reactions which are the result of highly coordinated sequential changes at the cellular level comprising, among other changes, the synthesis of signaling molecules. The ensuing plant responses are followed by the transmission of defense response signal cascades. Signals are mediated by bioactive endogenous molecules, i.e. phytohormones, such as jasmonic acid (JA), salicylic acid (SA), ethylene (ET), abscisic acid (ABA), gibberellic acid (GA) and free radicals such as hydrogen peroxide (H₂O₂) and nitric oxide (NO) which independently provide direct chemical resistance. Plant-induced defenses are also regulated by a network of inter-connecting signaling pathways, in which JA, SA, and ET play dominant roles. Both synergistic and inhibitory aspects of the cross-talk among these pathways have been reported. This paper presents molecular mechanisms of plant response to aphid feeding, the precise activation of various endogenous bioactive molecules signaling in the response of many plant species and their participation in the regulation of numerous defense genes, which lead to a specific metabolic effect. Selected important points in signal transduction pathways were also discussed in studies on plant response to aphid feeding.     

Elicitors and priming agents initiate plant defense responses

Biotic elicitors produced by plant pathogens or herbivore pests rapidly activate a range of plant chemical defenses when translocated to plant tissue. The fatty acid conjugate volicitin has proven to be a robust elicitor model for studying herbivore-induced plant defense responses. Here we review the role of insect-derived volicitin (N-[17-hydroxylinolenoyl]-L-glutamine) as an authentic elicitor of defense responses, specifically as an activator of signal volatiles that attract natural enemies of herbivore pests. Comparisons are drawn between volicitin as an elicitor of plant defenses and two other classes of signaling molecules, C₆ green-leaf volatiles and C₄ bacterial volatiles that appear to prime plant defenses thereby enhancing the capacity to mobilize cellular defense responses when a plant is faced with herbivore or pathogen attack.