Post-genomics of microsporidia, with emphasis on a model of minimal eukaryotic proteome: a review

The genome sequence of the microsporidian parasite Encephalitozoon cuniculi Levaditi, Nicolau et Schoen, 1923 contains about 2,000 genes that are representative of a non-redundant potential proteome composed of 1,909 protein chains. The purpose of this review is to relate some advances in the characterisation of this proteome through bioinformatics and experimental approaches. The reduced diversity of the set of E. cuniculi proteins is perceptible in all the compilations of predicted domains, orthologs, families and superfamilies, available in several public databases. The phyletic patterns of orthologs for seven eukaryotic organisms support an extensive gene loss in the fungal clade, with additional deletions in E. cuniculi. Most microsporidial orthologs are the smallest ones among eukaryotes, justifying an interest in the use of these compacted proteins to better discriminate between essential and non-essential regions. The three components of the E. cuniculi mRNA capping apparatus have been especially well characterized and the three-dimensional structure of the cap methyltransferase has been elucidated following the crystallisation of the microsporidial enzyme Ecm1. So far, our mass spectrometry-based analyses of the E. cuniculi spore proteome has led to the identification of about 170 proteins, one-quarter of these having no clearly predicted function. Immunocytochemical studies are in progress to determine the subcellular localisation of microsporidia-specific proteins. Post-translational modifications such as phosphorylation and glycosylation are expected to be soon explored.     

A genomics approach to crop pest and disease research

Genome-wide analyses of gene function and gene expression are beginning to yield valuable information in many areas of biological research, and these genomic tools are now being applied to crop pest and disease research. DNA sequencing of cDNA libraries to generate sets of expressed sequence tags (ESTs) are allowing gene compendiums for crop diseases to be compiled. Annotation of such data collections is also providing a wealth of functional information about gene products through similarities to proteins with known function. The next phase of the functional genomics era will be to employ large-scale techniques to knock out or silence genes in order to synthesize gene-specific mutants for phenotypic analysis and to use micro-array methodology to analyze global gene expression, protein turnover and protein processing during the processes of parasitism and colonization. Application of these technologies promises to accelerate the pace that biological information relevant to crop protection accrues. The ability of researchers to assimilate this information into complex models and workable hypotheses is, thus, set to revolutionize the way we study pests and diseases of crop plants.     

A review of the development of two types of human skeletal muscle infections from microsporidia associated with pathology in invertebrates and cold-blooded vertebrates

Traditionally, the Microsporidia were primarily studied in insects and fish. There were only a few human cases of microsporidiosis reported until the advent of AIDS, when the number of human microsporidian infections dramatically increased and the importance of these new pathogens to medicine became evident. Over a dozen different kinds of microsporidia infecting humans have been reported. While some of these infections were identified in new genera (Enterocytozoon, Vittaforma), there were also infections identified from established genera such as Pleistophora and Encephalitozoon. The genus Pleistophora, originally erected for a species described from fish muscle, and the genus Encephalitozoon, originally described from disseminated infection in rabbits, suggested a link between human infections and animals. In the 1980's, three Pleistophora sp. infections were described from human skeletal muscle without life cycles presented. Subsequently, the genus Trachipleistophora was established for a human-infecting microsporidium with developmental differences from species of the genus Pleistophora. Thus, the existence of a true Pleistophora sp. or spp. in humans was put into question. We have demonstrated the life-cycle stages of the original Pleistophora sp. infection from human muscle, confirming the existence of a true Pleistophora species in humans, P. ronneafiei Cali et Takvorian, 2003, the first demonstrated in a mammalian host. Another human infection, caused by a parasite from invertebrates, was Brachiola algerae Lowman, Takvorian et Cali, 2000. The developmental stages of this human muscle-infecting microsporidium demonstrate morphologically what we have also confirmed by molecular means, that B. algerae, the mosquito parasite, is the causative agent of this human skeletal muscle infection. B. algerae had previously been demonstrated in humans but only in surface infections, skin and eye. The diagnostic features of B. algerae and P. ronneafiei infections in human skeletal muscle are presented. While Encephalitozoon cuniculi has been known as both an animal (mammal) and human parasite, the idea of human microsporidial infections derived from cold-blooded vertebrates and invertebrates has only been suggested by microsporidian phylogeny based on small subunit ribosomal DNA sequences but has not been appreciated. The morphological data presented here demonstrate these relationships. Additionally, water, as a link that connects microsporidial spores in the environment to potential host organisms, is diagrammatically presented.     

Spinach: better management of downy mildew and white rust through genomics

Spinach (Spinacia oleracea) has become an increasingly important vegetable crop in many parts of the world. Significant changes in production practices, particularly in the U.S. and E.U., have occurred in the past 10–15 years as a result of increased product demand. These changes likely increased the incidence and severity of downy mildew, caused by Peronospora farinosa f. sp. spinaciae. Recently, progress has been made to define the genetics of resistance to this pathogen and the closely related white rust pathogen, Albugo occidentalis. In this paper, we outline the genetic and genomic resources currently available for spinach, draw parallels between spinach diseases and more thoroughly characterized pathosystems, and describe efforts currently underway to develop new genetic and genomic tools to better understand downy mildew and white rust of spinach. Presently, many crucial tools and resources required to define the molecular underpinnings of disease are unavailable for either spinach or its pathogens. New resources and information for spinach genomics would provide a jumpstart for ongoing efforts to define (and deploy) genetic resistance against downy mildew and white rust.     

Evolutionary strategies and adaptations for survival between mosquito-parasitic microsporidia and their intermediate copepod hosts: a comparative examination of Amblyospora connecticus and Hyalinocysta chapmani (Microsporidia: Amblyosporidae)

The epizootiology, transmission dynamics, and survival strategies employed by two mosquito-parasitic microsporidia that utilize copepods as intermediate hosts are examined in relation to the biological attributes of their hosts and the environments in which they inhabit. Amblyospora connecticus Andreadis, 1988, a parasite of Ochlerotatus cantator (Coquillett) and Acanthocyclops vernalis (Fischer) is found in an unstable salt marsh environment that is subject to periodic flooding and drying. Both hosts have distinct non-overlapping generations. A. connecticus exhibits a well-defined seasonal transmission cycle that relies heavily on maternal-mediated transovarial transmission by female O. cantator during the summer, and horizontal transmission via the copepod host during the spring (copepod to mosquito) and fall (mosquito to copepod). Its survival strategies include: delayed virulence, low pathogenicity and high tissue specificity that allow for transstadial transmission of horizontally acquired infections and maximum spore production, reliance on living hosts throughout most of its life cycle with overwintering in the copepod, polymorphic development that is well synchronized with host physiology, and production and dissemination of infectious spores that are coincident with the seasonal occurrence of susceptible stages in each host. Hyalinocysta chapmani Hazard et Oldacre, 1975, a parasite of Culiseta melanura (Coquillett) and Orthocyclops modestus (Herrick) is found in a comparatively stable, subterranean habitat that is inundated with water throughout the year. Copepods are omnipresent and C. melanura has overlapping broods. H. chapmani is maintained in a continuous cycle of horizontal transmission between each host throughout the summer and fall but lacks a developmental sequence leading to transovarial transmission in the mosquito host. It relies on living hosts for most of its life cycle and overwinters in diapausing mosquito larvae. Transstadial transmission does not occur and there is no dimorphic development in the mosquito host. The spatial and temporal overlap of both mosquito and copepod hosts during the summer and fall affords abundant opportunity for continuous horizontal transmission and increases the likelihood that H. chapmani will find a target host, thus negating the need for a transovarial route. It is hypothesized that natural selection has favoured the production of meiospores in larval female mosquitoes rather than congenital transfer of infection to progeny via ovarian infection as a strategy for achieving greater transmission success. Analysis of the molecular phylogeny data suggest that (1) transovarial transmission and the developmental sequence leading to ovarian infection have been secondarily lost in H. chapmani, as they occur in all other closely related genera, (2) the ancestral state included complex life cycles involving transovarial transmission and an intermediate host, and (3) mosquito-parasitic microsporidia are adjusting their life cycles to accommodate host ecological conditions.     

Comparative epidemiology of zoosporic plant pathogens

Loss of zoospores has happened independently several times in different phylogenic lines and has, it is claimed, no major phylogenetic significance. But whether or not, how, and under which conditions plant pathogens retain the ability to produce motile asexual spores has fundamental importance from an ecological and epidemiological perspective. Recent molecular investigations of the early evolution of fungi and oomycetes are shedding light on the issue of zoospore loss in organisms able to cause plant diseases. Zoospore loss may have accompanied the development of new forms of dispersal adapted to the terrestrial environment, or the simplification processes which often follow the shift to parasitic or biotrophic life-forms. In this review we consider hybridisation events between Phytophthora species, long distance dispersal of oomycetes, sporangia and zoospore survival, direct and indirect infection processes and newly observed sporulating structures. These aspects are all relevant features for an understanding of the epidemiology of zoosporic plant pathogens. Disease management should not be based on the presumption that the zoosporic stage is a weak link in the life cycle. Oomycete plant pathogens show remarkable flexibility in their life cycles and ability to adapt to changing environmental circumstances.

香蕉果实挥发物的化学成分比较分析

本文采用固相微萃取技术(SPME)收集成熟与未熟香蕉的挥发性物质,并运用气相色谱-质谱联用(GC-MS)对二者的化学成分进行种类和含量的比较分析。结果表明,两种香蕉果实的挥发性物质在种类和含量上存在明显差异,成熟香蕉中共检测出30种气味挥发性物质,而未熟香蕉中共检测出17种气味物质,且有多种化合物在成熟香蕉中存在而在未熟香蕉中未检测出。如成熟香蕉中的乙酸异戊酯、丁酸异丁酯、丁酸丁酯、2-庚醇-乙酸酯、异戊酸异戊酯、戊酸异戊酯和乙酸辛烯酯等7种物质的含量均明显高于未熟香蕉1以上。推测这些物质可能是成熟香蕉引诱桔小实蝇的活性物质。     

Comparative morphology of Phytophthora species on rubber

Eighty-nine Phytophthora isolates from rubber throughout the world were examined critically. Five species were distinguished: P. palmivora morphological form I (MF1), P. meadii, P. botryosa, P. citricola, P. citrophthora and one currently designated P. palmivora (MF4). P. citrophthora is reported for the first time from rubber in the Ivory Coast and Indonesia, and mating types are given.     

A diagnostic tool for improved detection of Xanthomonas fragariae using a rapid and highly specific LAMP assay designed with comparative genomics

Molecular diagnostics of plant pathogens are crucial to prevent disease spread and to enhance food quality and security. A comparative genomics approach using genomes of different Xanthomonas species and pathovars was applied to identify highly specific targets in the genome of Xanthomonas fragariae, the causal agent of angular leaf spot of strawberry, listed under quarantine regulations in Europe. A reliable and sensitive loop‐mediated isothermal amplification (LAMP) assay was designed using a unique marker, providing a highly specific and rapid detection technique, convenient for on‐site detection. Specificity of the designed assay was tested on 37 strains from a culture collection of X. fragariae, 82 strains of other Xanthomonas species and pathovars and 11 strains of other bacterial genera isolated from strawberry leaves. A detection limit of 10² fg was achieved, approximating to 20 genome copies per reaction. When performing analyses with crude plant material, a consistent lower detection efficiency of 10² CFU mL^?1 was achieved. The LAMP assay designed in this study was adapted to work on crude plant material without any prior extensive extraction steps or incubation period; moreover, it does not require advanced analytical knowledge or a fully equipped laboratory. Results were produced within 7–20 min, depending on the pathogen concentration, thus providing a high‐throughput and user‐friendly method for detection and screening of plant material in support of quarantine regulations.     

Comparative systemic translocation of several xenobiotics and sucrose

The systemic movement of several xenobiotics was compared in soybean and barley. The more symplastic compounds were also compared to the movement of sucrose. The uptake and efflux from potato tuber tissue was studied and related to the in vivo translocation patterns. The patterns of translocation ranged from primarily apoplastic to ambimobile to symplastic. When the percentage of xenobiotic available for translocation was evaluated there were major differences in patterns of translocation, between plant genera. In barley fenapanil, fenarimol, and oxamyl exhibited primarily apoplastic transport while all three were more ambimobile in soybean. Basipetal transport of oxamyl was 4.2% in barley compared to 30.8% in soybean. Basipetal translocation of benomyl remained very low at 3.0 and 4.1% in barley and soybean, respectively, while sucrose was about 60% in both species. Glyphosate and sucrose were translocated in a similar pattern. The transport of 2,4-D was primarily symplastic, however, retention in the tissue appeared to limit the rate of movement when compared to sucrose. Uptake and efflux of fenapanil, fenarimol, and 2,4-D illustrated the possible role that cellular binding or partitioning may play in systemic translocation. In conjunction with the uptake and efflux, and systemic movement in plants, the octanol/water partition coefficients, log P, for fenarimol and fenapanil, 0.67 and ?0.03, respectively, are correlated with the possible role of cellular binding or partitioning in the systemic movement of xenobiotics.     

Comparative effects of the herbicide dinitro-o-cresol on mitochondrial bioenergetics

The herbicide dinitro-o-cresol (DNOC) was evaluated for its effects on bioenergetic activities of potato tuber mitochondria to elucidate its mechanism of action and to compare its toxicological properties with those of the chemically related uncoupler dinitrophenol (DNP). DNOC acts as a typical uncoupler, similarly to the classical uncouplers DNP and carbonylcyanide p-trifluoromethoxyphenyl-hydrazone (FCCP). Low concentrations of DNOC (<100 μM ) maximally stimulate succinate-supported respiration of plant mitochondria, with simultaneous collapse of trans-membrane electrical potential, more efficiently than DNP. The herbicide makes the plant mitochondrial membrane more permeable to protons, acting as a protonophore even in non-energized mitochondria. High concentrations of DNOC (>100 μM ) act also more efficiently than DNP simultaneously as a protonophore and inhibitor of respiration, especially when respiration is supported by substrates that are transported to the matrix. The efficiency of DNOC is decreased with increase of mitochondrial protein, BSA and exogenous orthophosphate. Although similar effects were observed for animal and plant mitochondria, rat-liver mitochondrial respiration was more sensitive to DNOC than plant mitochondria. Furthermore, in the presence of DNOC, liver mitochondria exhibited a higher state 3 respiratory coupling level than potato tuber mitochondria, as a result of a considerable stimulation (60%) of state 3 respiration. In conclusion, DNOC is a more potent mitochondrial uncoupler and respiratory chain inhibitor than DNP, although their chemical structures are very similar. Apparently, the additional methyl group of DNOC increases its efficiency as an uncoupler and as an inhibitor, as compared to DNP. Plant mitochondria were shown to be as useful as animal mitochondria in evaluating the toxicity of these xenobiotics. © 1998 Society of Chemical Industry.     

Comparative tolerance of some dicotyledons to pronamide and chlorpropham

In laboratory tests with 115 species of dicotyledons, the concentration of pronamide in water for 50% inhibition of root elongation ranged from 0.03 to >8 parts/million. With certain exceptions, species within a family responded similarly. Polygonaceae and Caryophyllaceae were the most susceptible and Compositae the most tolerant, as they were also to chlorpropham. There was good correspondence between the test results and the relative susceptibility of species to pre-emergence application in the field.     

Comparative SAR Evaluations of Annonaceous Acetogenins for Pesticidal Activity

The activities of 44 Annonaceous acetogenins, which were originally isolated by monitoring plant fractionations with the brine shrimp lethality test (BST), were evaluated in the yellow fever mosquito larvae microtiter plate (YFM) assay. The results clearly demonstrate that most acetogenins have pesticidal properties. The structure–activity relationships indicate that the compounds bearing adjacent bis-THF (tetrahydrofuran) rings with three hydroxyl groups are the most potent. Bullatacin ( 1 ) and trilobin ( 7 ) gave the best activities against YFM with LC₅₀ values of 0·10 and 0·67 mg litre^-1, respectively. Compounds showing LC₅₀ values below 1·0 mg litre^-1 in this assay are usually considered significant as new lead candidates for pesticidal development. In the BST, the corresponding LC₅₀ values were 1·6×10^-3 ( 1 ) and 9·7×10^-3 ( 7 ) mg litre^-1. This is the first report of pesticidal structure–activity relationships for a series of Annonaceous acetogenins which are known to act, at least in part, as potent inhibitors of mitochondrial NADH: ubiquinone oxidoreductase. © of SCI.     

豆科3属6种植物叶片特征比较研究

运用石蜡切片技术和叶片解离技术对豆科6种植物的叶片特征进行研究,利用光学显微镜观察了3属6种豆科植物的叶表皮及叶片解剖结构,统计并测量了表皮细胞形状、垂周壁式样、表皮细胞面积、气孔大小、气孔密度、气孔指数、表皮厚度、叶片厚度、叶肉厚度、栅栏组织厚度、海绵组织厚度等相关的特征,并分析了叶片特征在种属之间存在的异同。结果表明:3属6种植物的气孔在上下表皮均有分布,气孔类型为不规则型,气孔形状均为椭圆形。表皮细胞形状、垂周壁式样、气孔密度、气孔指数、下表皮厚度、海绵组织厚度等指标在种属之间存在差异且具有一定的规律。分析显示:锦鸡儿属两种植物与草木樨属两种植物亲缘关系较近。     

Comparative analysis of flexible two-parameter models of plant disease epidemics

ABSTRACT Eleven previously published models of plant disease epidemics, given as differential equations with a rate and a shape parameter, are compared using general model characteristics as well as their usefulness in fitting observed data. Six out of the eleven models can be solved analytically resulting in epidemic growth functions, while the others can be solved only numerically. When all 11 differential equations were fitted to two data sets, all models showed a similar goodness of fit, although the shape parameter in some models could not be estimated very precisely. With respect to useful characteristics (exponential population growth at the beginning, ability to generate monomolecular disease progression, and flexibility of the inflection point), the models of Fleming, Kosman-Levy, Birch, Richards and Waggoner, and Rich are recommended. Formulas were established to calculate the point of inflection as well as the weighted absolute and relative rate, respectively, depending on the shape and rate parameter. These formulas allow transformation of the parameter values of one model into those of another model in many cases. If the two models are required to have the same temporal position of the disease progress curve, then the initial disease level at the start of the epidemic or the time when the inflection point is reached have to be transformed.     

5种景天科地被植物抗旱性比较研究

通过对5种景天科地被植物干旱胁迫处理后的丙二醛(MDA)含量、脯氨酸含量、可溶性总糖含量、相对含水量等指标的观察测定,评定了5种地被植物的抗旱性。结果表明:5种景天科地被植物均有一定的抗旱性,但抗旱性强弱不同,其中胭脂红景天抗旱性最强,其余抗旱性较弱。     

Comparative metabolism of famoxadone in fish,plants and animals

The fate and comparative metabolism of famoxadone in fish, plants and animals were evaluated. Famoxadone residues were retained by the fish after exposure (BCF 2800), mainly in the viscera; however, rapid and complete elimination/depuration of the absorbed residues occurred within seven days after the exposed fish were placed in untreated water. Minimal absorption, translocation, and metabolism of famoxadone were observed in grape and potato plants after foliar treatment. Metabolism of famoxadone in the wheat plants, rats, goats, and poultry was extensive. Transfer of ¹⁴C-residues to the wheat grain, milk, eggs, organs and tissues was minimal. Common metabolic reactions of famoxadone in plants and animals include aryl hydroxylation, cleavage of the anilino-oxazolidinedione and phenoxy-phenyl ether linkages, opening of the oxazolidinedione ring and conjugation.     

Comparative studies on graminicide-resistant and susceptible biotypes of Eleusine indica

A putative graminicide-resistant biotype of E. indica (L.) Gaertn. and a wild (graminicide sus ceptible) biotype were compared with regard to their growth, development and resistance to ary-loxyphenoxypropionate and cyclohexanedione herbicides in controlled environment studies. The resistant biotype produced much lower amounts of shoot biomass (46% less) but flow ered earlier and allocated a higher proportion and amount of biomass into seed-bearing struc tures compared with the wild type. The resistant biotype survived the application of 50 g a.i. ha^?1 of clethodim, tralkoxydim, sethoxydim, fluazi-fop-butyl, fenoxaprop-ethyl and diclofop methyl with the greatest resistance being shown to the aryloxyphenoxypropionates. At rates of >1000 g a.i. ha^?1, tralkoxydim achieved superior con trol to that of fluazifop-butyl. Even at rates of 4000 g a.i. ha^?1, some 50% of the resistant test plants survived the application of fluazifop-bu-tyl. The trait for graminicide resistance did not appear to be strongly heritable, as assessed by the growth and survival of a graminicide-treated F₁ population grown in isolation. It is concluded that widespread graminicide resistance in E. in dica is unlikely to develop from this biotype. Études comparatives de biotypes d'Eleusine indicata résistant et sensible aux herbicides à action antigraminée Un biotype d'Eleusine indica (L.) Gaertn., supposé résistant aux herbicides à action antigraminée, a été comparé en conditions contrôlées à un biotype sauvage (sensible) en ce qui concerne la croissance, le développement et la résistance aux herbicides aryoxyphénoxypropioniques et cyclohexanediones. Le biotype résistant produisait beaucoup moins de biomasse aérienne (-46%) mais fleurissait plus tôt et attribuait aux structures porteuses de graines une proportion et une quantité plus importantes de biomasse. Le biotype résistant survivait à un traitement à la dose 50 g ha^?1 de clethodime, de tralkoxydime, de séthoxydime, de fluazifop-butyle. de fénoxaprop-éthyle et de diclofop-méthyle, la plus grande résistance se manifestant à l'égard des aryloxyphénoxypropioniques. à des doses >1000 g m.a. ha^?1, le tralkoxydime était plus efficace que le fluazifop-butyle. Même à des doses 4000 g m.a. ha^?1, environ 50% des plantes résistantes survivaient à un traitement au fluazifop-butyle. Le caractère conférant la résistance aux herbicides à action antigraminée n'a pas montré de forte héritabilité, celle-ci étant estimée par la croissance et la survie d'une population F₁ traitée aux herbicides à action antigraminée et cultivée en isolement. En conclusion, il est peu probable qu'une résistance aux herbicides à action antigraminée se répande chez E. indicaà partir de ce biotype. Untersuchungen an Graminizid-resistenten und -toleranten Biotypen von Eleusine indica An einem wahrscheinlich Graminizid-resistenten und einem toleranten Biotyp von Eleusine indica (L.) Gaertn. wurden Wachstum, Entwicklung und Empfindlichkeit gegenüber Aryloxyphenoxypropionat- und Cyclohexandion-Her-biziden unter kontrollierten Bedingungen untersucht. Der resistente Biotyp hatte eine viel geringere Sproßbiomasse (46 % weniger), blühte aber früher und lagerte in die samenbildenden Organe einen größeren Anteil und Menge der Biomasse ein. Der resistente Biotyp überstand Behandlungen mit 50 g AS ha^?1 Clethodim, Tralkoxydim, Sethoxydim, Fluazi-fop-butyl, Fenoxaprop-ethyl und Diclofop-methyl. wobei die höchste Resistenz gegen die Aryloxyphenoxyproprionate bestand. Bei Aufwandmengen von >1000 g AS ha^?1 war die Bekämpfung mit Tralkoxydim besser als mit Fluazifop-butyl. Selbst bei Aufwandmengen von 4000 g AS ha^?1 Fluazifop-butyl lag die Wirkung auf die resistenten Pflanzen bei 50 %. Die Graminizidresistenz wurde nicht sicher vererbt, wie sich bei Untersuchungen des Wachstums und der Resitenz an F₁-Populationen zeigte, und eine weite Ausbreitung der Graminizidresistenz von diesem Biotyp aus wird bei Eleusine indica für wenig wahrscheinlich gehalten.