Phased chromosome-scale genome assembly of an asexual, allopolyploid root-knot nematode reveals complex subgenomic structure.

We present the chromosome-scale genome assembly of the allopolyploid root-knot nematode Meloidogyne javanica. We show that the M. javanica genome is predominantly allotetraploid, comprising two subgenomes, A and B, that most likely originated from hybridisation of two ancestral parental species.

Root-knot nematodes produce functional mimics of tyrosine-sulfated plant peptides.

Root-knot nematodes ( spp.) are highly evolved obligate parasites threatening global food security. These parasites have a remarkable ability to establish elaborate feeding sites in roots, which are their only source of nutrients throughout their life cycle.

Recognition and Response in Plant-Nematode Interactions.

Plant-parasitic nematodes spend much of their lives inside or in contact with host tissue, and molecular interactions constantly occur and shape the outcome of parasitism. Eggs of these parasites generally hatch in the soil, and the juveniles must locate and infect an appropriate host before their stored energy is exhausted. Components of host exudate are evaluated by the nematode and direct its migration to its infection site.

Plant metabolism of nematode pheromones mediates plant-nematode interactions.

Microorganisms and nematodes in the rhizosphere profoundly impact plant health, and small-molecule signaling is presumed to play a central role in plant rhizosphere interactions. However, the nature of the signals and underlying mechanisms are poorly understood. Here we show that the ascaroside ascr#18, a pheromone secreted by plant-parasitic nematodes, is metabolized by plants to generate chemical signals that repel nematodes and reduce infection.

Homologs of Chemosensory Genes Have Roles in Behavior and Chemotaxis in the Root-Knot Nematode .

Nematode chemosensation is a vital component of their host-seeking behavior. The globally important phytonematode perceives and responds (via sensory organs such as amphids and phasmids) differentially to various chemical cues emanating from the rhizosphere during the course of host finding. However, compared with the free-living worm , the molecular intricacies behind the plant nematode chemotaxis are a yet-unexploited territory.

Potent Attractant for Root-Knot Nematodes in Exudates from Seedling Root Tips of Two Host Species.

Root-knot nematodes (RKN; Meloidogyne spp.) can parasitize over 2,000 plant species and are generally considered to be the most agriculturally damaging group of plant-parasitic nematodes worldwide. Infective juveniles (J2) are non-feeding and must locate and invade a host before their reserves are depleted.

Comparative Genomics of Apomictic Root-Knot Nematodes: Hybridization, Ploidy, and Dynamic Genome Change.

The root-knot nematodes (genus Meloidogyne) are important plant parasites causing substantial agricultural losses. The Meloidogyne incognita group (MIG) of species, most of which are obligatory apomicts (mitotic parthenogens), are extremely polyphagous and important problems for global agriculture. While understanding the genomic basis for their variable success on different crops could benefit future agriculture, analyses of their genomes are challenging due to complex evolutionary histories that may incorporate hybridization, ploidy changes, and chromosomal fragmentation.

Assessing Attraction of Nematodes to Host Roots Using Pluronic Gel Medium.

Nematodes and other organisms perceive and respond to plant root exudates. These exudates are affected by the condition and genetic makeup of the plant. Attraction of the root-knot nematode Meloidogyne hapla to roots is altered in plants with mutations affecting ethylene signaling, suggesting that the root exudates to which the nematode responds are modulated by ethylene signaling.

Ethylene response pathway modulates attractiveness of plant roots to soybean cyst nematode Heterodera glycines.

Plant parasitic nematodes respond to root exudates to locate their host roots. In our studies second stage juveniles of Heterodera glycines, the soybean cyst nematode (SCN), quickly migrated to soybean roots in Pluronic F-127 gel. Roots of soybean and non-host Arabidopsis treated with the ethylene (ET)-synthesis inhibitor aminoethoxyvinylglycine (AVG) were more attractive to SCN than untreated roots, and significantly more nematodes penetrated into roots.

Conserved nematode signalling molecules elicit plant defenses and pathogen resistance.

Plant-defense responses are triggered by perception of conserved microbe-associated molecular patterns (MAMPs), for example, flagellin or peptidoglycan. However, it remained unknown whether plants can detect conserved molecular patterns derived from plant-parasitic animals, including nematodes. Here we show that several genera of plant-parasitic nematodes produce small molecules called ascarosides, an evolutionarily conserved family of nematode pheromones.

Mitochondrial haplotype-based identification of ethanol-preserved root-knot nematodes from Africa.

The asexual root-knot nematodes (RKNs) (Meloidogyne spp.) exemplified by Meloidogyne incognita are widespread and damaging pests in tropical and subtropical regions worldwide. Comparison of amplification products of two adjacent polymorphic regions of the mitochondrial genome using DNA extracts of characterized RKN strains, including 15 different species, indicate that several species are derived from the same or closely related female lineages.

An Translocation Confers Resistance Against Root-knot Nematodes to Common Wheat.

Root knot nematodes (RKN; spp.) cause severe losses worldwide to a wide range of crops. Crop rotations with resistant hosts can be used to control losses, but the wide host range of RKN limits this option.

Segregation and mapping in the root-knot nematode Meloidogyne hapla of quantitatively inherited traits affecting parasitism.

The root-knot nematode Meloidogyne hapla can reproduce on a wide range of crop species but there is variability in host range and pathogenicity both within and between isolates. The inbred strain VW9 causes galling but does not reproduce on Solanum bulbocastanum clone SB22 whereas strain VW8 causes little galling and reproduces poorly on this host. Comparison of reproduction on SB22 of nematode F2 lines generated from hybrids between strains VW8 and VW9 revealed that, whereas over half the lines produced no progeny, some lines reproduced to higher levels than did either parental strain.

A sequence-anchored linkage map of the plant-parasitic nematode Meloidogyne hapla reveals exceptionally high genome-wide recombination.

Root-knot nematodes (Meloidogyne spp.) cause major yield losses to many of the world's crops, but efforts to understand how these pests recognize and interact with their hosts have been hampered by a lack of genetic resources. Starting with progeny of a cross between inbred strains (VW8 and VW9) of Meloidogyne hapla that differed in host range and behavioral traits, we exploited the novel, facultative meiotic parthenogenic reproductive mode of this species to produce a genetic linkage map.

Ethylene signaling pathway modulates attractiveness of host roots to the root-knot nematode Meloidogyne hapla.

Infective juveniles of the root-knot nematode Meloidogyne hapla are attracted to the zone of elongation of roots where they invade the host but little is known about what directs the nematode to this region of the root. We found that Arabidopsis roots exposed to an ethylene (ET)-synthesis inhibitor attracted significantly more nematodes than control roots and that ET-overproducing mutants were less attractive. Arabidopsis seedlings with ET-insensitive mutations were generally more attractive whereas mutations resulting in constitutive signaling were less attractive.

Tm1: a mutator/foldback transposable element family in root-knot nematodes.

Three closely related parthenogenetic species of root-knot nematodes, collectively termed the Meloidogyne incognita-group, are economically significant pathogens of diverse crop species. Remarkably, these asexual root-knot nematodes are capable of acquiring heritable changes in virulence even though they lack sexual reproduction and meiotic recombination. Characterization of a near isogenic pair of M.

Root-knot nematodes exhibit strain-specific clumping behavior that is inherited as a simple genetic trait.

Root-knot nematodes are obligate parasites of a wide range of plant species and can feed only on the cytoplasm of living plant cells. In the absence of a suitable plant host, infective juveniles of strain VW9 of the Northern root-knot nematode, Meloidogyne hapla, when dispersed in Pluronic F-127 gel, aggregate into tight, spherical clumps containing thousands of worms. Aggregation or clumping behavior has been observed in diverse genera in the phylum Nematoda spanning free-living species such as Caenorhabditis elegans as well as both plant and animal parasites.

Determination of preferred pH for root-knot nematode aggregation using pluronic F-127 gel.

Root-knot nematodes (Meloidogyne spp.) are obligate endoparasites of a wide range of plant species. The infective stage is attracted strongly to and enters host roots at the zone of elongation, but the compounds responsible for this attraction have not been identified.

The genomes of root-knot nematodes.

Plant-parasitic nematodes are the most destructive group of plant pathogens worldwide and are extremely challenging to control. The recent completion of two root-knot nematode genomes opens the way for a comparative genomics approach to elucidate the success of these parasites. Sequencing revealed that Meloidogyne hapla, a diploid that reproduces by facultative, meiotic parthenogenesis, encodes approximately 14,200 genes in a compact, 54 Mpb genome.

Sequence and genetic map of Meloidogyne hapla: A compact nematode genome for plant parasitism.

We have established Meloidogyne hapla as a tractable model plant-parasitic nematode amenable to forward and reverse genetics, and we present a complete genome sequence. At 54 Mbp, M. hapla represents not only the smallest nematode genome yet completed, but also the smallest metazoan, and defines a platform to elucidate mechanisms of parasitism by what is the largest uncontrolled group of plant pathogens worldwide.

Silencing a candidate nematode effector gene corresponding to the tomato resistance gene Mi-1 leads to acquisition of virulence.

The Mi-1 gene in tomato confers effective resistance against several species of root-knot nematode, including Meloidogyne javanica. A strain of M. javanica that can reproduce on tomato with Mi-1 was obtained from a culture of an avirulent strain after greenhouse selection.

Meiotic parthenogenesis in a root-knot nematode results in rapid genomic homozygosity.

Many isolates of the plant-parasitic nematode Meloidogyne hapla reproduce by facultative meiotic parthenogenesis. Sexual crosses can occur, but, in the absence of males, the diploid state appears to be restored by reuniting sister chromosomes of a single meiosis. We have crossed inbred strains of M.

Introgressed and endogenous Mi-1 gene clusters in tomato differ by complex rearrangements in flanking sequences and show sequence exchange and diversifying selection among homologues.

Many plant disease resistance genes (R-genes) encode proteins characterized by the presence of a nucleotide-binding site (NBS) and a leucine-rich repeat (LRR) region and occur in clusters of related genes in plant genomes. One such gene, Mi-1, confers isolate-specific resistance against root-knot nematodes, aphids and whiteflies in cultivated tomato, Solanum lycopersicon. The DNA region carrying Mi-1 and six closely related sequences was introgressed into tomato from Solanum peruvianum in the 1940s.