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PubMed2003

Infection success in novel hosts: an experimental and phylogenetic study of Drosophila-parasitic nematodes.

Surprisingly little is known about what determines a parasite's host range, which is essential in enabling us to predict the fate of novel infections. In this study, we evaluate the importance of both host and parasite phylogeny in determining the ability of parasites to infect novel host species. Using experimental lab assays, we infected 24 taxonomically diverse species of Drosophila flies (Diptera: Drosophilidae) with five different nematode species (Tylenchida: Allantonematidae: Howardula, Parasitylenchus), and measured parasite infection success, growth, and effects on female host fecundity (i.e., virulence). These nematodes are obligate parasites of mushroom-feeding Drosophila, particularly quinaria and testacca group species, often with severe fitness consequences on their hosts. We show that the potential host ranges of the nematodes are much larger than their actual ranges, even for parasites with only one known host species in nature. Novel hosts that are distantly related from the native host are much less likely to be infected, but among more closely related hosts, there is much variation in susceptibility. Potential host ranges differ greatly between the related parasite species. All nematode species that successfully infected novel hosts produced infective juveniles in these hosts. Most novel infections did not result in significant reductions in the fecundity of female hosts, with one exception: the host specialist Parasitylenchus nearcticus sterilized all quinaria group hosts, only one of which is a host in nature. The large potential host ranges of these parasites, in combination with the high potential for host colonization due to shared mushroom breeding sites, explain the widespread host switching observed in comparisons of nematode and Drosophila phylogenies.

Animals↗
PubMed2000

Cloning and characterization of an extremely conserved satellite DNA family from the root-knot nematode Meloidogyne arenaria.

A new satellite DNA family, named pMaE, has been cloned from the genome of the phytoparasitic nematode, Meloidogyne arenaria (Nematoda: Tylenchida). It is represented as tandemly repeated sequences with a monomeric unit of 172 bp. The monomers are present at approximately 15700 copies per haploid genome, and represent about 5.3% of the total genomic DNA. Twenty-seven independent monomers have been cloned and sequenced. The deduced consensus sequence is 70.9% A + T rich, with frequent stretches of A and (or) T. Several direct or inverted sub-repeats are present in the sequence, which may allow the formation of a dyad structure, suggesting some potential role of this repetitive sequence in heterochromatin condensation. The monomers are very homogeneous in sequence, showing on average 1.8% divergence from their consensus sequence. Moreover, Southern blot experiments and sequence analysis of homologous monomers from the genome of geographically distinct M. arenaria populations have shown that this satellite DNA is uniformly distributed and highly conserved within the species. Therefore, it is hypothesized that this unusually low level of variability, either within the genome of a given population or between populations, could be achieved as the result of some highly effective homogenization mechanism acting upon the nematode genome.

Animals↗
PubMed2004

Evolution of plant parasitism among nematodes.

Despite extraordinary diversity of free-living species, a comparatively small fraction of nematodes are parasites of plants. These parasites represent at least three disparate clades in the nematode tree of life, as inferred from rRNA sequences. Plant parasites share functional similarities regarding feeding, but many similarities in feeding structures result from convergent evolution and have fundamentally different developmental origins. Although Tylenchida rRNA phylogenies are not fully resolved, they strongly support convergent evolution of sedentary endoparasitism and plant nurse cells in cyst and root-knot nematodes. This result has critical implications for using model systems and genomics to identify and characterize parasitism genes for representatives of this clade. Phylogenetic studies reveal that plant parasites have rich and complex evolutionary histories that involve multiple transitions to plant parasitism and the possible use of genes obtained by horizontal transfer from prokaryotes. Developing a fuller understanding of plant parasitism will require integrating more comprehensive and resolved phylogenies with appropriate choices of model organisms and comparative evolutionary methods.

Animals↗
PubMed1975

Use of hot formaldehyde fixative in processing plant-parasitic nematodes for electron microscopy.

A preparative technique is formulated for processing plant-parasitic nematodes of the order Tylenchida for electron microscopy. A population of Dolichodorus heterocephalus is used as test objects. One and a half grams of paraformaldehyde are dissolved in 25 ml of water at 60 C. Five drops of 1 N sodium hydroxide are added to clear the solution, which is then cooled to room temperature. Two and a half milliliters of 25% glutaraldehyde are added with 23 ml 0.1 M phosphate buffer, pH 7.3, and 0.2 M with respect to sucrose. The final solution contains 3% formaldehyde and 1% glutaraldehyde and is pH 7.2. It is heated to 70 C, poured over specimens, and allowed to cool to 4 C in 2 hr. The nematodes are then incised in a fixative containing 2% glutaraldehyde and 5% dimethyl sulfoxide at 4 C for 16-24 hr. Five milliliters of 25% glutaraldehyde and 2.5 ml of dimethyl sulfoxide are combined in 17.5 ml of water. Twenty-five milliliters of phosphate buffer (supplemented as above) are added. The final pH is 7.2. The glutaraldehyde, aided by dimethyl sulfoxide, uniformly and permanently fixes the nematode tissues. The specimens are embedded in agar. Following a 30-min buffer wash (4 C) they are postfixed in buffered 2% osmium tetroxide for 2 hr at room temperature, washed, and dehydrated through an ethanol series and two acetone baths. Dehydration includes a 2-hr stop in 75% ethanol containing 2% uranyl acetate. After embedding in Spurr's epoxy resin, specimens are sectioned and poststained in 0.5% aqueous acetate for 6 min and saturated aqueous lead citrate 3--4 min. This technique reduces killing time to less than 2 sec, straightens specimens for easier orientation, and eliminates the typically high internal pressure of nematodes which causes displacement of internal structures observed with other fixation techniques.

Animals↗
PubMed2005

Biodiversity of nematofauna of oilseed rape (Brassica napus L.).

Few data is available on the nematodes found in Brassicaceae, except for the most important plant parasite. However, studying the structure of nematofauna could be an important database for the soil quality and in order to assess the effects of future disturbance. This is particularly important considering that the diffusion of the canola crop in the world is increasing because of its use as a bio-diesel. Very diffused is also the Bt variety of oil seed rape, and, in this case, the study of the impact on the soil health and on bio-diversity is essential. In this research we have analyzed the nematode community, used as a bio-indicator of the soil condition. The nematofauna found in canola (Brassica napus var. oleifera) fields located in Southern Italy (Metaponto - MT) was investigated. The nematode community was studied considering its abundance, genus composition and trophic structure. Maturity and biodiversity indices were also calculated. A total of 5286 nematodes were extracted. They belong to 14 families and 24 genera. Bacterial and fungal feeders, 50.18% and 42.90% of the total respectively, dominated the trophic structure. Aphelencus is the most abundant genus (23.71%) followed by Acrobeloides (20.49%) and Aphelencoides (19.18%). Among plant feeders (6.59%), Pratylenchus is the dominant genus (2.20%) and Tylenchidae the main family (3.54%). No infestation of Meloidogyne, Heterodera or Naboccus, important plant-parasitic nematodes of canola crops, was recorded. Other important phytophagous were Helycotylenchus (0.5%), Trichotylenchus (0.5%) and Filenchus (0.9%). All of them had an abundance level below injury level. The indices of biodiversity are rather low (H'=0.93, J'=0.67), as is typical for agro ecosystems. However, the nematofauna community is quite well structured (N2=6.31, D=0.16) and the maturity index rather high (EMI=1.94). These values demonstrate that oilseed rape has a lower impact on the soil compared to other crop systems and that it could be taken into consideration for crop rotation programs. Canola could follow other more stressful crops, trying to maintain soil equilibrium.

Agriculture↗
PubMedDate not supplied

[Morphogenesis of the genital system in the superfamily Tylenchoidea (Nematoda)].

Morphogenesis of the genital system of 14 species of nematodes of the superfamily Tylenchoidea was studied. The evolution of the genital system of females in the superfamily was considered. The initial type for the group is a paired gonade of the females. In different families the reduction of the hind branch of the gonade proceeds in parallel. During ontogenesis the development of the posterior part of the trophicogenital department and the gonade branch restrains. In the family Pratylenchidae this phenomenon is associated with the shortening of the body during the transition to endoparasitism; in the family Tylenchidae the phenomenon is connected with the acquiring of the streamline form suitable for living in humid biotopes. In the family Anguinidae takes place the hypertrophy of the female genital system connected with the transition to the cavitary endoparasitism. A new technique for making preparations of nematodes is suggested.

Biological Evolution↗
PubMed1995

Species identification of cyst and root-knot nematodes from potato by electrophoresis of individual females.

To carry out rapid and reliable species identification of Globodera and Meloidogyne specimens, two electrophoretic methods were modified and adapted for an automated electrophoresis system (PhastSystem, Pharmacia). Proteins of individual Globodera cysts were identified using isoelectric focusing and a sensitive silver stain. Proteins of young single Meloidogyne females were separated using polyacrylamide gradient gels and stained for the isozymes esterase and malate dehydrogenase.

Animals↗
PubMed2003

Location of independent root-knot nematode resistance genes in plum and peach.

Prunus species express different ranges and levels of resistance to the root-knot nematodes (RKN) Meloidogyne spp. In Myrobalan plum ( Prunus cerasifera), the dominant Ma gene confers a high-level and wide-spectrum resistance to the predominant RKN, Meloidogyne arenaria, Meloidogyne incognita, Meloidogyne javanica and the isolate Meloidogyne sp. Florida which overcomes the resistance of the Amygdalus sources. In Japanese plum ( Prunus salicina), a similar wide-spectrum dominant resistance gene, termed R(jap), has been hypothesized from an intraspecific segregating cross. In peach, two crosses segregating for resistance to both M. incognita and M. arenaria were used to identify single genes that each control both RKN species in the Shalil ( R(Mia557)) and Nemared ( R(MiaNem)) sources. Localisation of these genes was made possible using the RFLP and SSR- saturated reference Prunus map TxE, combined with a BSA approach applied to some of the genes. The Ma1 allele carried by the Myrobalan plum accession P.2175 was localised on the linkage group 7 at an approximate distance of 2 cM from the SSR marker pchgms6. In the Japanese plum accession J.222, the gene R(jap) was mapped at the same position in co-segregation with the SSR markers pchgms6 and CPPCT022. The peach genes R(Mia557) and R(MiaNem), carried by two a priori unrelated resistance sources, were co-localized in a subtelomeric position on linkage group 2. This location was different from the more centromeric position previously proposed by Lu et al. (1999) for the resistance gene Mij to M. incognita and M. javanica in Nemared, near the SSR pchgms1 and the STS EAA/MCAT10. By contrast, R(Mia557) and R(MiaNem) were flanked by STS markers obtained by Yamamoto and Hayashi (2002) for the resistance gene Mia to M. incognita in the Japanese peach source Juseitou. Concordant results for the three independent sources, Shalil, Nemared and Juseitou, suggest that these peach RKN sources share at least one major gene resistance to M. incognita located in this subtelomeric position. We showed that plum and peach genes are independent and, thus, can be pyramided into interspecific hybrid rootstocks based on the plum and peach species.

Animals↗
PubMed2004

Physiology and molecular characteristics of a pine wilt nematode-trapping fungus, Monacrosporium megalosporum.

We isolated the nematode-trapping fungus Monacrosporium megalosporum from nature and examined its morphology, physiology and molecular characteristics. The nematode-trapping device of this fungus is a three-dimensional network. This fungus captures the pine wilt nematode (Bursaphelenchus xylophilus), but not a non-phytopathogenic nematode that is morphologically similar to B. xylophilus. The phylogenic relationship of the nucleotide sequence of the rDNA ITS region was close to those of M. thaumasium and Geniculifera eudermata, which also have nematode-trapping devices that are three-dimensional networks. Acidic pH inhibited both the liberation and regeneration of protoplasts. Moreover, cytoplasmic granulation of protoplasts was found below pH 6.0. Mycelial growth on agar media was also inhibited below pH 4, but not at pH 9. These results strongly suggest that the activity of this fungus is inhibited by acid rain in the field. Therefore, development of pine wilt disease might be a secondary effect of acid rain.

Animals↗
PubMed2005

Assessment of nematode resistance in wheat transgenic plants expressing potato proteinase inhibitor (PIN2) gene.

Serine proteinase inhibitors (IP's) are proteins found naturally in a wide range of plants with a significant role in the natural defense system of plants against herbivores. The question addressed in the present study involves assessing the ability of the serine proteinase inhibitor in combating nematode infestation. The present study involves engineering a plant serine proteinase inhibitor (pin2) gene into T. durum PDW215 by Agrobacterium-mediated transformation to combat cereal cyst nematode (Heterodera avenae) infestation. Putative T(0) transformants were screened and positive segregating lines analysed further for the study of the stable integration, expression and segregation of the genes. PCR, Southern analysis along with bar gene expression studies corroborate the stable integration pattern of the respective genes. The transformation efficiency is 3%, while the frequency of escapes was 35.71%. chi(2) analysis reveals the stable integration and segregation of the genes in both the T(1) and T(2) progeny lines. The PIN2 systemic expression confers satisfactory nematode resistance. The correlation analysis suggests that at p < 0.05 level of significance the relative proteinase inhibitor (PI) values show a direct positive correlation vis-à-vis plant height, plant seed weight and also the seed number.

Animals↗
PubMed2005

Origin, distribution and 3D-modeling of Gr-EXPB1, an expansin from the potato cyst nematode Globodera rostochiensis.

Southern analysis showed that Gr-EXPB1, a functional expansin from the potato cyst nematode Globodera rostochiensis, is member of a multigene family, and EST data suggest expansins to be present in other plant parasitic nematodes as well. Homology modeling predicted that Gr-EXPB1 domain 1 (D1) has a flat beta-barrel structure with surface-exposed aromatic rings, whereas the 3D structure of Gr-EXPB1-D2 was remarkably similar to plant expansins. Gr-EXPB1 shows highest sequence similarity to two extracellular proteins from saprophytic soil-inhabiting Actinobacteria, and includes a bacterial type II carbohydrate-binding module. These results support the hypothesis that a number of pathogenicity factors of cyst nematodes is of procaryotic origin and were acquired by horizontal gene transfer.

Amino Acid Sequence↗
PubMed2005

Resolving tylenchid evolutionary relationships through multiple gene analysis derived from EST data.

Sequence-based phylogenetic analyses typically are based on a small number of character sets and report gene trees which may not reflect the true species tree. We employed an EST mining strategy to suppress such incongruencies, and recovered the most robust phylogeny for five species of plant-parasitic nematode (Meloidogyne arenaria, M. chitwoodi, M. hapla, M. incognita, and M. javanica), three closely related tylenchid taxa (Heterodera glycines, Globodera pallida, and G. rostochiensis) and a distant taxon, Caenorhabditis elegans. Our multiple-gene approach is based on sampling more than 80,000 publicly available tylenchid EST sequences to identify phylum-wide orthologues. Bayesian inference, minimum evolution, maximum likelihood and protein distance methods were employed for phylogenetic reconstruction and hypothesis tests were constructed to elucidate differential selective pressures across the phylogeny for each gene. Our results place M. incognita and M. javanica as sister taxa, with M. arenaria as the next closely related nematode. Significant differences in selective pressure were revealed for some genes under some hypotheses, though all but one gene are exclusively under purifying selection, indicating conservation across the orthologous groups. This EST-based multi-gene analysis is a first step towards accomplishing genome-wide coverage for tylenchid evolutionary analyses.

Animals↗
PubMed1997

The 5.8S rDNA sequences of 18 species of bursate nematodes (order Strongylida): comparison with rhabditid and tylenchid nematodes.

The 5.8S rDNA sequences of 18 species of bursate nematode were 153 bp in length and had a G + C content of 47-50%. Interspecific differences in rDNA sequence among the bursate nematodes were low (0-5.2%), but the extent of the sequence differences between the parasitic bursate nematodes, a free-living rhabditid nematode and 2 species of parasitic tylenchid nematodes (12-33%) suggests that the 5.8S rRNA gene may provide useful phylogenetic information with respect to the relationships of the different orders within the phylum Nematoda.

Animals↗