Biology subjects

Williamson, V. M.

Publications and source records attributed to Williamson, V. M..

7 recordsLinked to original sources

bioRxiv2026

Resistance Breaking in Root-knot Nematodes Carries a Fitness Cost Associated with Defective Feeding Site Development

Root-knot nematodes (RKNs) cause an estimated 157 billion dollars in annual yield losses worldwide. In tomato, resistance to RKNs is conferred by the single dominant resistance gene Mi-1, which has been widely integrated into commercial cultivars. Prolonged and widespread use of Mi-1 has led to the emergence of resistance-breaking populations in tomato fields worldwide; however, the consequences of resistance breaking for nematode performance on susceptible hosts remain poorly understood. Here, we compared infection outcomes of two closely related strains of Meloidogyne javanica, VW4 (Mi-1-avirulent; wild-type) and VW5 (Mi-1-virulent; resistance-breaking), on three susceptible hosts: tomato, cucumber, and rice. Across all hosts, VW5 produced significantly fewer eggs than VW4, revealing a fitness cost associated with Mi-1 virulence. Light and transmission electron microscopy of tomato and cucumber galls revealed impaired feeding site establishment by VW5. Consistent with these observations, transcriptomic profiling showed that VW5 infection induced weaker host transcriptional reprogramming and lacked gene expression signatures associated with effective suppression of plant defense responses. Together, these findings demonstrate that adaptation to Mi-1-mediated resistance incurs a fitness cost on susceptible plants and is accompanied by impaired feeding site formation and altered host reprogramming. Furthermore, these results establish VW4 and VW5 as a powerful resource for understanding nematode genes and pathways required for successful parasitism and feeding site development.

plant biology↗

bioRxiv2025

Genomic and Transcriptomic Insights into the Evolution and Parasitic Strategy of the Woody-Plant Nematode Pratylenchus vulnus

The root-lesion nematode Pratylenchus vulnus parasitizes a wide range of hosts including woody perennials such as walnut (Juglans regia) and grapevine (Vitis vinifera), significantly damaging roots and reducing yields. Here, we present a high-quality, chromosome-level genome assembly of P. vulnus (61.7 Mb across six chromosomes). Comparative genomic analysis revealed high collinearity in protein-coding genes between P. vulnus and the root-knot nematode Meloidogyne graminicola, indicating a closer evolutionary relationship with this sedentary endoparasite. Large chromosomal regions in P. vulnus lack synteny with other nematode genomes, have comparatively low GC content (<30%), and are enriched in genes with unique or lineage-specific functions. Transcriptome analysis highlighted dynamic, stage-specific expressions of genes involved in parasitism, development, and metabolism. Additionally, we identified an extensive repertoire of putative effector genes and characterized lineage-specific expansions of cell wall-degrading enzyme families. Overall, these findings provide insight into the genome organization, chromosome evolution, and parasitism-related gene repertoire in a woody-plant parasitizing nematode.

plant biology↗

bioRxiv2025

N6-Methyladenine DNA modification regulates pathogen virulence in nematodes

Understanding the global regulatory mechanisms that control pathogen virulence gene expression is essential for elucidating the molecular basis of pathogenicity. N6-methyladenine (6mA) plays a crucial role in regulating gene expression in response to various environmental stresses; however, its role in pathogen virulence remains largely unexplored. Here, we report the widespread occurrence of 6mA across 17 nematode isolates and map its genomic landscape in six notorious agriculturally important pathogen root-knot nematodes (RKNs). We demonstrated that 6mA is characterized by a conserved GAG motif across nematodes, but exhibits species-specific distribution patterns and distinct effects on gene expression. In particular, its enrichment in transposable elements differs between polyploid and diploid nematodes, suggesting lineage-specific epigenetic regulation potentially associated with polyploidy. We further identified two functional 6mA demethylases, MiNMAD-1 and MiNMAD-2, and confirmed their catalytic activity and active sites. Host-induced gene silencing of minmad-1 significantly increased plant resistance to three polyploid RKN species. A detailed functional analysis revealed that minmad-1 knockdown disrupted virulence gene expression during the parasitic stage, thereby reducing nematode infectivity. Together, our findings suggest 6mA demethylase as a key epigenetic regulator of RKNs virulence, providing new insights into nematode biology and offering promising targets for the development of sustainable control strategies. Significance Statement6mA methyltransferase regulates the expression of virulence genes in certain pathogenic bacteria and plays a critical role in their infectivity. However, the regulation of virulence gene expression in eukaryotic pathogens, particularly plant pathogens, remains poorly understood. Most studies on pathogen virulence have focused on individual effectors, with little insight into global regulatory mechanisms. Here, we demonstrate that 6mA broadly shapes virulence gene expression patterns in polyploid RKNs. Moreover, transgenic tobacco, tomato, and rice plants expressing dsRNA against nematode demethylases showed significantly enhanced resistance to RKNs. These findings establish 6mA demethylase as a promising epigenetic target for controlling plant-parasitic nematodes.

molecular biology↗

bioRxiv2025

A Chromosome-scale Reference Genome of Meloidogyne hapla reveals localized recombination hotspots enriched with Effector Proteins

Root-knot nematodes (Meloidogyne spp.) are among the most destructive agricultural pests that cause significant yield losses across a wide range of crops. Meloidogyne hapla, a diploid species, is a valuable model for studying root-knot nematodes due to its parasitic diversity, small genome, and a reproductive strategy that facilitates genetic analysis. Here, we present a high-quality chromosome-scale assembly of M. hapla, generated using multiple sequencing platforms-PacBio HiFi, ONT, Illumina and HiC. The 59 Mb assembly comprises 16 chromosome-length scaffolds, notably lacking canonical telomeric repeats. Instead, we identified a tandem 16-mer repeat mainly present at scaffold ends, suggesting an alternative system for chromosome-end maintenance. Genetic linkage analysis of F2 populations derived from crosses between M. hapla strains validated the assembly but also revealed anomalies indicating chromosome structure differences between parental isolates such as fissions, fusions, and rearrangements. This analysis also revealed sharply delineated zones of high recombination on most chromosome arms. We also identified 1,258 genes encoding putative secreted proteins (PSP), which should be enriched in genes involved in host interaction and pathogenicity. Most of the PSP genes had orthologs in other plant parasitic nematode species, and the majority were pioneers, lacking known functional domains. Notably, we found that PSPs are significantly enriched in high-recombination zones, possibly facilitating their rapid evolution. Overall, our study provides new insights into the genome structure of diploid root-knot nematodes and highlights the interplay between genome architecture, recombination, and parasitism. These findings raise new questions about how genetic and genomic adaptations drive the success of rootknot nematodes as plant parasites.

plant biology↗

bioRxiv2023

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

We present the chromosome-scale genome 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. The assembly is annotated using full-length non-chimeric transcripts, comparison to reference databases, and ab initio prediction techniques, and the subgenomes are phased using ancestral k-mer spectral analysis. Subgenome B appears to show greater fission of chromosomal contigs, and while there is substantial synteny between subgenomes, we also identify regions lacking synteny that may have diverged in the ancestral genomes prior to or following hybridisation. Indels are common both between alleles within a subgenome, and between the A and B subgenomes, suggesting the M. javanica genome exists in a dynamic hypo-tetraploidy where copy number can vary along the chromosome. This annotated and phased genome assembly forms a significant resource for understanding the origins and genetics of these globally important plant pathogens. Author SummaryRoot-knot nematodes represent one of the most significant crop parasites globally. Despite their agricultural importance, only rudimentary genomic resources have been published to date, leaving a gap in the understanding of genetic mechanisms driving genome evolution and crop virulence. Here, we have used modern genomic and bioinformatic approaches to create a chromosome-scale reference genome to investigate the origins and genomic constitution of the root-knot nematode species Meloidogyne javanica. This species reproduces by ameiotic parthenogenesis and has an allopolyploid genome and is among the most damaging plant parasitic nematodes with a large and evolving plant host range. Utilising modern long-range DNA sequencing and bioinformatics approaches, we successfully phased the genome into its constituent subgenomes, a first for this agriculturally important clade. While we find the genomic landscape is mostly syntenic between subgenomes, we identified regions of minimal similarity, and highlight structural divergence between subgenomes. We demonstrate that this species was originally tetraploid, but insertions and deletions have been the major force in generating diversity, resulting in a hypo-tetraploid genome with local variations in ploidy.

genomics↗

bioRxiv2022

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

Root-knot nematodes (Meloidogyne spp.) are highly evolved obligate parasites that threaten 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. A wide range of nematode effectors have been implicated in modulation of host pathways for feeding site development. Plants produce a diverse array of peptide hormones including plant peptides containing sulfated tyrosine (PSYs), which promote root growth via cell expansion and proliferation. A sulfated PSY-like peptide RaxX (required for activation of XA21 mediated immunity X) produced by the biotrophic bacterial pathogen (Xanthomonas oryzae pv. oryzae), has been previously shown to contribute to bacterial virulence. Here, we report the identification of genes from root-knot nematodes predicted to encode PSY-like peptides (MigPSYs) with high sequence similarity to both bacterial RaxX and plant PSYs. Sulfated synthetic peptides corresponding to predicted MigPSYs stimulate root growth in Arabidopsis. MigPSY transcript levels are highest early in the infection cycle. Down-regulation of MigPSY gene expression reduces root galling and egg production, suggesting that the MigPSYs serve as nematode virulence factors. Together these results indicate that nematodes and bacteria utilize similar sulfated peptides to hijack plant developmental signaling pathways to facilitate parasitism.

plant biology↗

bioRxiv2017

Comparative Genomics Of Apomictic Root-Knot Nematodes: Hybridization, Ploidy, And Dynamic Genome Change

The Root-Knot Nematodes (RKN; 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 pose challenges due to complex evolutionary histories that may incorporate hybridization, ploidy changes, and chromosomal fragmentation. Here we sequence 19 genomes, representing five species of key RKN collected from different geographic origins. We show that a hybrid origin that predated speciation within the MIG has resulted in each species possessing two divergent genomic copies. Additionally, the MIG apomicts are hypotriploids, with a proportion of one genome present in a second copy, and this proportion varies among species. The evolutionary history of the MIG genomes is revealed to be very dynamic, with non-crossover recombination both homogenising the genomic copies, and acting as a mechanism for generating divergence between species. Interestingly, the automictic MIG species M. floridensis differs from the apomict species in that it has become homozygous throughout much of its genome.

evolutionary biology↗