Characterization of the venom allergen—like protein (vap-1) and the fatty acid and retinol binding protein (far-1) genes in Meloidogyne hispanica
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Fatty acid methyl ester (FAME) analysis has been utilized to identify bacteria and some fungi, but little progress has been made to identify nematodes using this system. A series of samples containing varying numbers of individuals of Meloidogyne incognita, Rotylenchulus reniformis, and Heterodera glycines was used to determine the applicability of FAME analysis for identification of these three nematode species, quantify the minimum number of individuals required for identification, identify samples containing mixed-species populations, and evaluate the impact of plant host species on nematode fatty acid profiles. All three nematode genera were correctly identified with unique FAME profiles. A minimum of 100 vermiform stage nematodes was required for accurate identification of M. incognita, and R. reniformis while 25 cysts were required to identify H. glycines. Different ratios of mixed-species samples of M. incognita and R. reniformis could be identified with greater than 83% accuracy. Fatty acid profiles of M. incognita and R. reniformis varied significantly (P < 0.0001) when grown on each of three different host plants, though the increased variation within the two species did not inhibit identification of either species. By
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The sophisticated parasitic tactic of sedentary endoparasitic nematodes seems to involve the simultaneous alteration of the expression of multitude of its effector genes in order to hijack the plant metabolic and developmental pathway. In concordance with this hypothesis, we have targeted some candidate effector genes of Meloidogyne incognita to understand the possible interaction among those effectors for successful infection of the host plant. In vitro RNAi strategy was used to knock down M. incognita -specific pioneer effector genes, such as msp-18 , msp-20 , msp-24 , msp-33 and msp-16 (known to interact with plant transcription factor), to investigate their possible effect on the expression of key cell wall-degrading enzymes (CWDE) and vice versa . Supported by the phenotypic data, intriguingly our study revealed that induced suppression of these pioneer genes cause transcriptional alteration of CWDE genes in M. incognita . This remarkable finding may provide some useful links for future research on nematode effector interaction.
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Tioxazafen is a seed-applied nematicide used in row crops. Currently, there are no data on nematode toxicity, nematode recovery, or effects of low concentrations of tioxazafen on nematode infection of a host root for Meloidogyne incognita or Rotylenchulus reniformis. Nematode toxicity and recovery experiments were conducted in water solutions of tioxazafen, while root infection assays were conducted on tomato. Nematode paralysis was observed after 24 hr of exposure at 27.0 µg/ml tioxazafen for both the nematode species. Based on an assay of nematode motility, 24-hr EC50 values of 57.69 µg/ml and 59.64 µg/ml tioxazafen were calculated for M. incognita and R. reniformis, respectively. Tioxazafen rates of 2.7 µg/ml and 27.0 µg/ml reduced the nematode hatch after 3 d of exposure for both the nematode species. There was no recovery in nematode motility after the 24-hr exposure of M. incognita and R. reniformis to their corresponding 48-hr EC50 values of 47.15 µg/ml and 47.25 µg/ml tioxazafen, respectively. Mortality of M. incognita continued to increase after 24 hr exposure, whereas R. reniformis mortality remain unchanged after nematodes were rinsed and removed for 48 hr from the tioxazafen solution. A 24-hr exposure to low concentrations of 0.38 to 47.15 µg/ml for M. incognita and 47.25 µg/ml for R. reniformis reduced the infectivity of each nematode species on tomato roots. The toxicity of tioxazafen was similar between nematode species; however, a greater rate of tioxazafen was needed to suppress R. reniformis infection of tomato than for M. incognita.
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Rotylenchulus reniformis
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Root-knot nematode
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ABSTRACT The root-knot nematode Meloidogyne incognita is a major pathogen of a range of important crops. Currently, control is typically achieved by the use of nematicides. However, recent work suggests that manipulating the ability of roots to slough off border cells, which then act as a decoy to the nematode, can significantly decrease damage to the roots. We investigated the attractiveness of border cells to M. incognita and the response of the nematode to border cells in close proximity. We found very limited attraction, in that nematodes did not preferentially alter direction to move toward the border cells, but a large and significant increase in nematode speed was observed once they were in the immediate vicinity of border cells. We discuss the results in the context of physical and biological mechanisms in relation to the control of pathogenic nematodes.
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The tethered-nematode technique was adapted for use with second-stage juveniles of Meloidogyne incognita. The data demonstrate that M. incognita exhibits the same patterns of behavior as adults of the free-living nematode, Caenorhabditis elegans. The principal differences are that M. incognita is slower and less regular in its behavior than C. elegans. The frequency of normal waves is about 0.2 Hz; that of reversal waves is about 0.06 Hz. Reversal bouts last about 1 minute. In response to a change in NaCl concentration, M. incognita modulates the probability of initiating a reversal bout in the same manner as C. elegans except that it responds more slowly and is repelled instead of attracted.
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The type III secretion system (TTSS) is a key mechanism for host cell interaction used by a variety of bacterial pathogens and symbionts of plants and animals including humans. The TTSS represents a molecular syringe with which the bacteria deliver effector proteins directly into the host cell cytosol. Despite the importance of the TTSS for bacterial pathogenesis, recognition and targeting of type III secreted proteins has up until now been poorly understood. Several hypotheses are discussed, including an mRNA-based signal, a chaperon-mediated process, or an N-terminal signal peptide. In this study, we systematically analyzed the amino acid composition and secondary structure of N-termini of 100 experimentally verified effector proteins. Based on this, we developed a machine-learning approach for the prediction of TTSS effector proteins, taking into account N-terminal sequence features such as frequencies of amino acids, short peptides, or residues with certain physico-chemical properties. The resulting computational model revealed a strong type III secretion signal in the N-terminus that can be used to detect effectors with sensitivity of ∼71% and selectivity of ∼85%. This signal seems to be taxonomically universal and conserved among animal pathogens and plant symbionts, since we could successfully detect effector proteins if the respective group was excluded from training. The application of our prediction approach to 739 complete bacterial and archaeal genome sequences resulted in the identification of between 0% and 12% putative TTSS effector proteins. Comparison of effector proteins with orthologs that are not secreted by the TTSS showed no clear pattern of signal acquisition by fusion, suggesting convergent evolutionary processes shaping the type III secretion signal. The newly developed program EffectiveT3 (http://www.chlamydiaedb.org) is the first universal in silico prediction program for the identification of novel TTSS effectors. Our findings will facilitate further studies on and improve our understanding of type III secretion and its role in pathogen–host interactions.
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