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A virus with a large genome was identified in the transcriptome of the potato aphid (Macrosiphum euphorbiae) and was named Macrosiphum euphorbiae virus 1 (MeV-1). The MeV-1 genome is 22 780 nt in size, including 3' and 5' non-coding regions, with a single large ORF encoding a putative polyprotein of 7333 aa. The C-terminal region of the predicted MeV-1 polyprotein contained sequences with similarities to helicase, methyltransferase and RNA-dependent RNA polymerase (RdRp) motifs, while the N-terminal region lacked any motifs including structural proteins. Phylogenetic analysis of the helicase placed MeV-1 close to pestiviruses, while the RdRp region placed it close to pestiviruses and flaviviruses, suggesting MeV-1 has a positive-polarity ssRNA genome and is a member of the family Flaviviridae. Since the MeV-1 genome is predicted to contain a methyltransferase, a gene present typically in flaviviruses but not pestiviruses, MeV-1 is likely a member of the genus Flavivirus. MeV-1 was present in nymphal and adult stages of the aphid, aphid saliva and plant tissues fed upon by aphids. However, the virus was unable to multiply and spread in tomato plants. In addition, dsRNA, the replication intermediate of RNA viruses, was isolated from virus-infected M. euphorbiae and not from tomato plants infested with the aphid. Furthermore, nymphs laid without exposure to infected plants harboured the virus, indicating that MeV-1 is an aphid-infecting virus likely transmitted transovarially. The virus was present in M. euphorbiae populations from Europe but not from North America and was absent in all other aphid species tested.

Heterodera glycines, the soybean cyst nematode (SCN), is a plant-parasitic nematode capable of manipulating host plant biochemistry and development. Many studies have suggested that the nematode has acquired genes from bacteria via horizontal gene transfer events (HGTs) that have the potential to enhance nematode parasitism. A recent allelic imbalance analysis identified two candidate virulence genes, which also appear to have entered the SCN genome through HGTs. One of the candidate genes, H. glycines biotin synthase (HgBioB), contained sequence polymorphisms between avirulent and virulent inbred SCN strains. To test the function of these HgBioB alleles, a complementation experiment using biotin synthase-deficient Escherichia coli was conducted. Here, we report that avirulent nematodes produce an active biotin synthase while virulent ones contain an inactive form of the enzyme. Moreover, sequencing analysis of HgBioB genes from SCN field populations indicates the presence of diverse mixture of HgBioB alleles with the virulent form being the most prevalent. We hypothesize that the mutations in the inactive HgBioB allele within the virulent SCN could result in a change in protein function that in some unknown way bolster its parasitic lifestyle.

Two important race groups of the stem nematode, Ditylenchus dipsaci, an obligatory polyphagous endoparasite, attack the bean, Vicia faba. Morphological differences have been found in the two groups and there were corresponding differences in faba bean disease symptoms. Agreement has been found between RAPD and phenotypic characteristics in the nematodes. Variation between D. dipsaci species in populations involved with V. faba was low. No strong correlation was found between geographical origin and morphological or molecular characteristics.

Heterodera glycines, the soybean cyst nematode (SCN), is a plantparasitic nematode capable of manipulating host plant biochemistry and development. Many studies have suggested that the nematode has acquired genes from bacteria via horizontal gene transfer events (HGTs) that have the potential to enhance nematode parasitism. A recent allelic imbalance analysis identified two candidate virulence genes, which also appear to have entered the SCN genome through HGTs. One of the candidate genes, H. glycines biotin synthase (HgBioB), contained sequence polymorphisms between avirulent and virulent inbred SCN strains. To test the function of these HgBioB alleles, a complementation experiment using biotin synthasedeficient Escherichia coli was conducted. Here, we report that avirulent nematodes produce an active biotin synthase while virulent ones contain an inactive form of the enzyme. Moreover, sequencing analysis of HgBioB genes from SCN field populations indicates the presence of diverse mixture of HgBioB alleles with the virulent form being the most prevalent. We hypothesize that the mutations in the inactive HgBioB allele within the virulent SCN could result in a change in protein function that in some unknown way bolster its parasitic lifestyle. [ABSTRACT FROM AUTHOR]

The pretreatment of Arabidopsis with red light (600–700 nm) induces systemic resistance against root-knot nematode Meloidogyne javanica and Pseudomonas syringae pv. tomato DC 3000. Red light treatment significantly (P = 0.05) reduced the number of root galls in both wild type (Col-0) and nahG-expressing Arabidopsis compared with those of white light-treated control plants, while red light treatment only induced resistance to P. syringae in wild-type plants. This result suggests that red light induces resistance against root-knot nematode in Arabidopsis through a transduction pathway, which is independent of salicylic acid (SA) accumulation in roots, but resistance to P. syringae is SA-dependent. PR1 gene expression was monitored as a marker for systemic acquired resistance (SAR). Relative quantification of expression of the PR1 gene corresponding to the cDNA was examined in both leaves and roots. There was no significant difference between leaves and roots of red light-treated Arabidopsis in quantitative PR1 gene expression. In red light-treated wild type (Col-0) Arabidopsis, PR1 mRNA was induced by 23.11- and 22.47-fold for leaf and root, respectively, compared with the plants treated with white light. However, in nahG plants, PR1 gene expression changed only by 0.4-fold. These findings indicate that plant defense responses activated by the foliar SA-dependent pathway depend on the specific host–pathogen system. This is the first report of red light-induced resistance in Arabidopsis against root-knot nematode. [ABSTRACT FROM AUTHOR]

Two sets of experiments in 1998 and 1999 studied the (a)virulence status of 14 populations of Heterodera avenae, and two populations each of H. filipjevi and H. latipons towards the resistance genes and genotypes of Triticeae, presently known to be resistant to H. avenae, the main species of the cereal cyst nematode (CCN) species complex. Susceptible controls were Triticum aestivum cv. Arminda and Triticum turgidum cv. Cham1. Even in controlled experimental conditions, host responses differed between replicates in the same test and between consecutive tests for unexplained reasons. In spite of that, it has been confirmed that several of these CCN populations differ in their intrinsic capacity to reproduce, and this has to be taken into account in resistance screening. Consequently, the (a)virulence status of a CCN population is better established by a qualitative demarcation between resistant and susceptible plant genotypes based on an average of one cyst limit per plant. The matrix inferred from such a classification of host responses of pooled 1998 and 1999 data showed a complex distribution of avirulent and virulent phenotypes in these CCN populations which seems to arise from a mosaic-like evolution. The more or less wide virulence spectrum shown by this complex of populations and species is discussed in relation to their phylogenetic relationships. Correspondence factor analysis of the pooled data demonstrated a geographical demarcation between several populations of H. avenae and the representatives of H. filipjevi and H. latipons for their (a)virulence to either Cre1 or Cre3 genes and T. aestivum AUS4930 genotype. This could reveal local or regional selection of new pathotypes, more particularly in H. avenae. Genetic introgression to improve resistance to these nematodes in both bread and durum wheats is discussed for regional and global applications. [ABSTRACT FROM AUTHOR]

Heterodera glycines is a nematode that is highly adapted to manipulate and parasitize plant hosts. The molecular players involved in these interactions have only recently begun to be identified. Here, the sequencing of the second stage juvenile transcriptome, followed by a bioinformatic screen for novel genes, identified seven new genes involved in biosynthesis and salvage of vitamins B₁, B₅, and B₇. With no confirmed reports in the literature, each of these biosynthesis pathways is believed to have been lost in multicellular animals. However, eukaryotic-like introns in the genomic sequences of the genes confirmed eukaryotic origin and nematode-specific splice leaders found on five of the cDNAs confirmed their nematode origin. Two of the genes were found to be flanked by known nematode sequences and quantitative polymerase chain reactions on individual nematodes showed similar and consistent amplification between the vitamin B biosynthesis genes and other known H. glycines genes. This further confirmed their presence in the nematode genome. Similarity to bacterial sequences at the amino acid level suggested a prokaryotic ancestry and phylogenetic analysis of the genes supported a likely horizontal gene transfer event, suggesting H. glycines re-appropriated the genes from the prokaryotic kingdom. This finding complements the previous discovery of a vitamin B₆ biosynthesis pathway within the nematode. However, unlike the complete vitamin B₆ pathway, many of these vitamin B pathways appear to be missing the initial enzymes required for full de novo biosynthesis, suggesting that initial substrates in the pathways are obtained exogenously. These partial vitamin B biosynthesis enzymes have recently been identified in other single-celled eukaryotic parasites and on rhizobia symbiosis plasmids, indicating that they may play an important role in host-parasite interactions and survival within the plant environment.