线虫耐寒性研究进展

对于分布在温带和寒带的线虫,它们只有战胜冬季寒冷的挑战,才能有利于种群的存在与发展。因此,耐寒性是线虫生物学研究中不可忽视的内容。综述了关于线虫在低温胁迫下的耐寒性测定方法、耐寒对策及耐寒机制等方面的研究进展。线虫的耐寒性和昆虫一样,可通过过冷却点和低温存活率两种指标进行评价,但在具体的实验方法上,线虫耐寒性研究有其不同之处。线虫的耐寒对策和耐寒机制具有多样化。耐寒对策主要有耐冻和避冻,二者能共同渗透于线虫的耐寒过程中。耐寒机制包括特殊发育阶段的形成、低温驯化作用、低分子量抗冻物质的聚集、以及高分子量抗冻蛋白和热休克蛋白的产生,等等。此外,还强调应从多个角度研究线虫的耐寒性,如寒冷敏感型线虫的研究、寄生线虫的耐寒对策研究以及交叉胁迫的研究。     

Metalloid tolerance based on phytochelatins is not functionally equivalent to the arsenite transporter Acr3p

Active transport of metalloids by Acr3p and Ycf1p in Saccharomyces cerevisiae and chelation by phytochelatins in Schizosaccharomyces pombe, nematodes, and plants represent distinct strategies of metalloid detoxification. In this report, we present results of functional comparison of both resistance mechanisms. The S. pombe and wheat phytochelatin synthase (PCS) genes, when expressed in S. cerevisiae, mediate only modest resistance to arsenite and thus cannot functionally compensate for Acr3p. On the other hand, we show for the first time that phytochelatins also contribute to antimony tolerance as PCS fully complement antimonite sensitivity of ycf1Delta mutant. Remarkably, heterologous expression of PCS sensitizes S. cerevisiae to arsenate, while ACR3 confers much higher arsenic resistance in pcsDelta than in wild-type S. pombe. The analysis of PCS and ACR3 homologues distribution in various organisms and our experimental data suggest that separation of ACR3 and PCS genes may lead to the optimal tolerance status of the cell.     

An overview of arbuscular mycorrhizal fungi–nematode interactions

Plant parasitic nematodes and arbuscular mycorrhizal fungi (AMF) share plant roots as a resource for food and space. The interest in AMF-nematode interactions lies in the possibility of enhanced resistance or tolerance of AMF-infected plants to nematodes, and the potential value of this for control of crop pests. Data collated from previous studies revealed a great diversity of AMF-nematode responses and we seek to generalise from these by evaluating and discussing interactions involving three groups of nematodes distinguished by their mode of parasitism: (i) ectoparasites; (ii) sedentary endoparasites; and (iii) migratory endoparasites. Based on proximity in tissue, we expected that the interactions between endoparasites and AMF would be stronger, i.e. more reciprocal effects of endoparasitic nematodes on AMF, than those between ectoparasites and AMF. Contrary to this hypothesis, we found that, relative to AMF-free plants, AMF-infected plants were damaged more by ectoparasites than by endoparasites. Of the sedentary endoparasites, numbers of root-knot nematodes were reduced more by mycorrhizal infection than were those of cyst nematodes. The reduction in nematode damage by AMF was not different for root-knot or cyst nematode infested plants. Migratory endoparasitic nematodes were the only group whose numbers were greater on AMF-infected plants. However, the experiments involving migratory nematodes were characterised by relatively high levels of AMF infection and little nematode damage compared to the other feeding types. The outcomes of the AMF-nematode interactions are determined by many factors during the interactions between organisms and their physical, physiological and temporal environments. Assessing effects by recording plant sizes and total nematode or AMF populations at the end of experiments gives very little information on the mechanisms of the interactions. It is time to stop doing studies of black boxes and time to start observing processes, directly by using microscopy and indirectly by application of molecular genetics.     

Genomics of reproduction in nematodes: prospects for parasite intervention?

Understanding reproductive processes in parasitic nematodes has the potential to lead to the informed design of new anthelmintics and control strategies. Little is known, however, about the molecular mechanisms underlying sex determination, gametogenesis and reproductive physiology for most parasitic nematodes. Together with comparative analyses of data for the free-living nematode Caenorhabditis elegans, molecular investigations are beginning to provide insights into the processes involved in reproduction and development in parasitic nematodes. Here, we review recent developments, focusing on technological aspects and on molecules associated with sex-specific differences in adult nematodes.     

The environmental physiology of Antarctic terrestrial nematodes: a review

The environmental physiology of terrestrial Antarctic nematodes is reviewed with an emphasis on their cold-tolerance strategies. These nematodes are living in one of the most extreme environments on Earth and face a variety of stresses, including low temperatures and desiccation. Their diversity is low and declines with latitude. They show resistance adaptation, surviving freezing and desiccation in a dormant state but reproducing when conditions are favourable. At high freezing rates in the surrounding medium the Antarctic nematode Panagrolaimus davidi freezes by inoculative freezing but can survive intracellular freezing. At slow freezing rates this nematode does not freeze but undergoes cryoprotective dehydration. Cold tolerance may be aided by rapid freezing, the production of trehalose and by an ice-active protein that inhibits recrystallisation. P. davidi relies on slow rates of water loss from its habitat, and can survive in a state of anhydrobiosis, perhaps aided by the ability to synthesise trehalose. Teratocephalus tilbrooki and Ditylenchus parcevivens are fast-dehydration strategists. Little is known of the osmoregulatory mechanisms of Antarctic nematodes. Freezing rates are likely to vary with water content in Antarctic soils. Saturated soils may produce slow freezing rates and favour cryoprotective dehydration. As the soil dries freezing rates may become faster, favouring freezing tolerance. When the soil dries completely the nematodes survive anhydrobiotically. Terrestrial Antarctic nematodes thus have a variety of strategies that ensure their survival in a harsh and variable environment. We need to more fully understand the conditions to which they are exposed in Antarctic soils and to apply more natural rates of freezing and desiccation to our studies.Communicated by: I.D. Hume     

The living strategy of nematophagous fungi

The infection structures, trophism, and ecological character of nematophagous fungi are reviewed in this article on the basis of data extracted from the literature and the most recent experiments conducted in this area. Traditionally, nematophagous fungi are classified into four groups according to their modes of attacking nematodes: nematode-trapping fungi using adhesive or mechanical hyphal traps, endoparasitic fungi using their spores, eggparasitic fungi invading nematode eggs or females with their hyphal tips, and toxin-producing fungi immobilizing nematodes before invasion. In the present review, we focus on the first two groups. The living strategies of these nematophagous fungi depend on the diversity of their infection structures, such as different traps and spore types, which determine the modes of infecting nematodes. The diversity of trophic modes of nematophagous fungi is an important prerequisite for fungal survival and activity in soil. The abundance and activity of Hirsutella rhossiliensis and H. minnesotensis, representatives of endoparasites and potential biocontrol agents against nematodes, are highly dependent on environmental factors. Comprehensive understanding of the survival and activity of nematophagous fungi in soil is fundamental for the exploitation of these fungi as successful biocontrol agents.     

Detection and Description of Soils with Specific Nematode Suppressiveness

Soils with specific suppressiveness to plant-parasitic nematodes are of interest to define the mechanisms that regulate population density. Suppressive soils prevent nematodes from establishing and from causing disease, and they diminish disease severity after initial nematode damage in continuous culturing of a host. A range of non-specific and specific soil treatments, followed by infestation with a target nematode, have been employed to identify nematode-suppressive soils. Biocidal treatments, soil transfer tests, and baiting approaches together with observations of the plant-parasitic nematode in the root zone of susceptible host plants have improved the understanding of nematode-suppressive soils. Techniques to demonstrate specific soil suppressiveness against plant-parasitic nematodes are compared in this review. The overlap of studies on soil suppressiveness with recent advances in soil health and quality is briefly discussed. The emphasis is on methods (or criteria) used to detect and identify soils that maintain specific soil suppressiveness to plant-parasitic nematodes. While biocidal treatments can detect general and specific soil suppressiveness, soil transfer studies, by definition, apply only to specific soil suppressiveness. Finally, potential strategies to exploit suppressive soils are presented.     

The effect of manganese deficiency and cereal cyst nematode infection on the growth of barley

Summary Two factorial pot experiments, each with four rates of soil-applied manganese (Mn), four levels of cereal cyst nematodes (CCN) and four replicates, were conducted under controlled environmental conditions to investigate the interaction of these factors on growth of barley. The experiments were harvested sequentially to count numbers of nematodes at two developmental stages. Development of the nematodes was independent of the Mn status of the host, indicating no effect of Mn on host resistance. In the absence of CCN, decreased Mn had a small effect on vegetative growth, not significantly decreasing dry weight of tops but tolerance at the higher densities of CCN was considerably reduced at low Mn supply, both vegetative growth and grain yield being depressed. Increasing CCN density exerted little effect on the growth of Mn sufficient hosts. Two field surveys supported conclusions from the pot experiments in that increasing nematode densities were correlated with decreasing plant size only at the site where plants were low in Mn. An implication for the field is that crops infected with the nematode and also low in Mn may yield less than expected because the two factors interact to reduce growth and retard development.     

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.     

植物耐盐性研究进展

土壤盐渍化是影响农业生产和生态环境的严重问题,耕地的减少和淡水资源的不足将迫使人类开发和利用大面积的盐碱地、海岸带和滩涂地带,植物耐盐的机理和耐盐植物的培育研究将成为研究的热点。本文就植物的耐盐性、植物中各种渗透调节剂及植物耐盐相关基因等方面近十年的研究进展作一概要的评价 。     

Tolerance of thermophilic and hyperthermophilic microorganisms to desiccation

We examined short- and long-term desiccation tolerance of 31 strains of thermophilic and hyperthermophilic Archaea and thermophilic phylogenetically deep-branching Bacteria. Seventeen organisms showed a significant high ability to withstand desiccation. The desiccation tolerance turned out to be species-specific and was influenced by several parameters such as storage temperature, pH, substrate or presence of oxygen. All organisms showed a higher survival rate at low storage temperatures (−20°C or below) than at room temperature. Anaerobic and microaerophilic strains are influenced negatively in their survival by the presence of oxygen during desiccation and storage. The desiccation tolerance of Sulfolobales strains is co-influenced by the pH and the substrate of the pre-culture. The distribution of desiccation tolerance in the phylogenetic tree of life is not domain specific. Surprisingly, there are dramatic differences in desiccation tolerance among organisms from the same order and even from closely related strains of the same genus. Our results show that tolerance of vegetative cells to desiccation is a common phenomenon of thermophilic and hyperthermophilic microorganisms although they originated from quite different non-arid habitats like boiling acidic springs or black smoker chimneys.     

Endosymbionts of arthropods and nematodes: allies to fight infectious diseases?

Arthropods and nematodes are important protagonists in human health because either they act as vectors of pathogens (bacteria, protozoa, viruses or fungus), or are themselves parasites. Fighting infectious diseases is based essentially on vaccination (prevention) or chemotherapeutic (curative) approaches in human, but one can envisage as an alternative to reduce the number of vectors or limit their ability to spread pathogens. Such strategies controlling dissemination will undoubtedly benefit from the knowledge accumulated by recent works on powerful mechanisms developed by symbiotic insect bacteria such as Wolbachia to popagate in arthropods and nematods. This review summarizes these recent data, and indicate how these mechanisms can be manipulated to reduce the dissemination of insect vectors propagating human diseases.     

Control of foliar phytoparasitic nematodes through sustainable natural materials: Current progress and challenges

Nematodes are hidden enemies that inhibit the entire ecosystem causing adverse effects on animals and plants, leading to economic losses. Management of foliar phytoparasitic nematodes is an excruciating task. Various approaches were used to control nematodes dispersal, i.e., traditional practices, resistant cultivars, plant extract, compost, biofumigants, induced resistance, nano-biotechnology applications, and chemical control. This study reviews the various strategies adopted in combating plant-parasitic nematodes while examining the benefits and challenges. The significant awareness of biological and environmental factors determines the effectiveness of nematode control, where the incorporation of alternative methods to reduce the nematodes population in plants with increasing crop yield. The researchers were interested in explaining the fundamental molecular mechanisms, providing an opportunity to deepen our understanding of the sustainable management of nematodes in croplands. Eco-friendly pesticides are effective as a sustainable nematodes management tool and safe for humans. The current review presents the eco-friendly methods in controlling nematodes to minimize yield losses, and benefit the agricultural production efficiency and the environment.     

昆虫病原线虫对非生物胁迫的响应机制

昆虫病原线虫是农林害虫生物防治中重要的生防因子之一。它对非生物胁迫的耐受能力决定着线虫在田间的个体生存及控制害虫效果。线虫对环境胁迫的响应是一个整体性的复杂过程, 体现在群体遗传、发育阶段、生理生化和抗逆相关基因的表达调控等不同层次、不同水平上。本文综述了昆虫病原线虫抗逆相关领域的主要研究进展, 重点介绍线虫响应非生物胁迫的生理生化机制和相关抗性基因的分离鉴定, 并对该研究领域发展趋势进行了讨论和展望, 期望为我国研究线虫抗逆机理提供一些新的信息。     

Engineering Natural and Synthetic Resistance for Nematode Management

Bioengineering strategies are being developed that will provide specific and durable resistance against plant-parasitic nematodes in crops. The strategies come under three categories: (i) transfer of natural resistance genes from plants that have them to plants that do not, to mobilize the defense mechanisms in susceptible crops; (ii) interference with the biochemical signals that nematodes exchange with plants during parasitic interactions, especially those resulting in the formation of specialized feeding sites for the sedentary endoparasites—many nematode genes and many plant genes are potential targets for manipulation; and (iii) expression in plant cells of proteins toxic to nematodes.     

Tolerance and chronic rejection

The most common cause of chronic allograft loss is an incompletely understood clinicopathological entity called chronic rejection (CR). Recent reports suggest an improvement in long-term renal allograft survival, although it is not clear from these data whether a true reduction of biopsy-proven CR has occurred. Although newer immunosuppressive medications have greatly reduced the incidence of acute rejection (AR) in the early post-transplantation period, the ideal therapy for both AR and CR would be to achieve a state of tolerance. By definition, such a state should allow for indefinite allograft survival, with no histopathological evidence of CR, despite immunocompetence in the host (i.e. without the need for chronic immunosuppression). Although several experimental studies are able to achieve tolerance, with clear improvement in allograft survival, detailed studies on graft function and morphology are often not included. This review will discuss possible ways that tolerance induction could lead to a CR-free state. General mechanisms of CR and transplantation tolerance induction are discussed as well as the difficulties in translating small animals studies into large animals and humans.     

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.     

Heat‐shock proteins and cross‐tolerance in plants

Environmental stresses dramatically affect plant survival and productivity. Because plants are immobile, presumably different strategies are required for protection against transient stresses. Under stress, plants synthesize specific proteins, and their accumulation has a role in protecting the tissue from possible damage. An increasing number of studies show the existence of cross‐tolerance in plants: Exposure of tissue to moderate stress conditions often induces resistance to other stresses. Many varied mechanisms explaining the phenomenon of cross‐tolerance have been proposed, and they often, but not always, suggest that specific proteins are induced by one kind of stress and are involved in the protection against other kinds. Although various cross‐protections have been demonstrated in a number of plants, a common mechanism has not been found. This review discusses heat‐shock proteins and their possible roles in protecting the plant under heat and other stresses.     

The importance of being regular: Caenorhabditis elegans and Pristionchus pacificus defecation mutants are hypersusceptible to bacterial pathogens

Bacterial pathogens have shaped the evolution and survival of organisms throughout history, but little is known about the evolution of virulence mechanisms and the counteracting defence strategies of host species. The nematode model organisms, Caenorhabditis elegans and Pristionchus pacificus, feed on a wealth of bacteria in their natural soil environment, some of which can cause mortality. Previously, we have shown that these nematodes differ in their susceptibility to a range of human and insect pathogenic bacteria, with P. pacificus showing extreme resistance compared with C. elegans. Here, we isolated 400 strains of Bacillus from soil samples and fed their spores to both nematodes. Spores of six Bacillus strains were found to kill C. elegans but not P. pacificus. While the majority of Bacillus strains are benign to nematodes, observed pathogenicity is restricted to either the spore or the vegetative stage. We used the rapid C. elegans killer strain (Bacillus sp. 142) to conduct a screen for hypersusceptible P. pacificus mutants. Two P. pacificus mutants with severe muscle defects and an extended defecation cycle that die rapidly on Bacillus spores were isolated. These genes were identified to be homologous to C. elegans, unc-22 and unc-13. To test whether a similar relationship between defecation and bacterial pathogenesis exists in C. elegans, we used five known defecation mutants. Quantification of the defecation cycle in mutants also revealed a severe effect on survival in C. elegans. Thus, intestinal peristalsis is critical to nematode health and contributes significantly to survival when fed Gram-positive bacteria.     

Role for rpoS gene of Pseudomonas aeruginosa in antibiotic tolerance

The alternative sigma factor, RpoS has been described as a central regulator of many stationary phase-inducible genes and a master stress-response regulator under various stress conditions. We constructed an rpoS mutant in Pseudomonas aeruginosa and investigated the role of rpoS gene in antibiotic tolerance. The survival of the rpoS mutant cells in stationary phase was approximately 70 times lower when compared with that of the parental strain at 37 degrees C for 2 h after the addition of biapenem. For imipenem, the survival was approximately 40 times lower. Heat stress promoted an increase in the survival of the parental strain to biapenem, but the same was not found to be the case for the rpoS mutant. Our results indicate that rpoS gene is involved in tolerance to antibiotics in P. aeruginosa during the stationary phase and heat stress. However, under osmotic stress, tolerance to biapenem was not dependent on the rpoS gene.