Biology subjects

Van Ghelder, C.

Publications and source records attributed to Van Ghelder, C..

6 recordsLinked to original sources

bioRxiv2026

Large parallel deletions are associated with massive gene losses and virulence acquisition in Meloidogyne incognita

The root-knot nematode Meloidogyne incognita is a major constraint to crop production worldwide. The resistance gene Mi-1.2 has been widely deployed in tomato varieties to control this parasite. However, virulent nematode isolates, overcoming the Mi-1.2-mediated resistance, have increasingly emerged in fields. Understanding the genetic mechanisms underlying resistance circumvention is therefore essential towards sustainable crop protection. From two geographically distinct M. incognita avirulent isolates, previous experimental evolution assays have allowed producing two virulent M. incognita isolates that escaped Mi-1.2 resistance in tomato. Here, we investigated the transcriptomic and genomic changes in the two virulent M. incognita isolates, as compared to their avirulent progenitor isolates controlled by the resistance. First, our transcriptomic analyses revealed hundreds of strongly downregulated genes, in common, in both virulent isolates. Most of these downregulated genes are clustered in two main genome regions. Long-read whole-genome sequencing of the four isolates revealed parallel structural variations in both virulent isolates. This included two large deletions spanning ca. 1.3 Mb and 0.6 Mb. The two big deletions encompass clusters of downregulated genes, suggesting they have in fact been lost in both virulent isolates. Short-read genome sequencing and PCR validation confirmed the two deletions in the two virulent isolates. The largest deletion includes predicted effector and orphan genes. The parallel large-scale structural variations identified here are likely to underlie the rapid adaptation of M. incognita to Mi-1.2-mediated resistance. These findings highlight genome structural plasticity as one of the potential key drivers of virulence acquisition in these asexually reproducing parasites.

evolutionary biology↗

bioRxiv2026

Transcriptional responses of Solanum lycopersicum to three distinct parasites reveal host hubs and networks underlying parasitic successes

Crops face attacks from a wide range of pathogens and pests that deploy various parasitic strategies. All aggressors must manipulate major plant functions, such as immune signaling, hormone pathways, metabolism, and development, to successfully establish themselves and complete their life cycle. Here, we compared the tomato plant's response to three evolutionary distant pathogens (nematodes, aphids and oomycetes) during compatible interactions using a transcriptomic approach. We identified differentially expressed genes and biological processes, and highlighted potential key host hubs associated with successful parasitism. By integrating recent published datasets, we refined our understanding of the global and tissue-specific mechanisms targeted during compatible interactions and, through co-expression analysis, identified clusters showing shared dysregulation patterns enriched in specific GO terms. Finally, model-to-crop translational analysis using the Arabidopsis interactome network, repositioned tomato candidates within larger interaction networks and emphasized the key positions occupied by some of them. Identifying these pivotal tomato targets is crucial to decipher processes underlying parasitism and, consequently, offers new opportunities to develop sustainable multi-pathogen control strategies.

plant biology↗

bioRxiv2025

Chromosome-scale genome assembly of Xiphinema index uncovers an unparalleled epigenetic toolkit in invertebrates

Nematodes constitute the most speciose animal phylum, occupying an exceptionally broad range of biomes and encompassing free-living microbe-feeders, predators, and notorious plant or animal parasites. However, the limited availability of genome-scale resources for early-branching nematode clades has constrained our understanding of the molecular determinants underlying these multiple evolutionary adaptations. Here, we present the genome of the plant-parasitic nematode Xiphinema index, constituting the first telomere-to-telomere assembly for the order Dorylaimida, an early-branching nematode lineage. Phylogenetic analyses reveal that horizontal gene transfers (HGT) have played a pivotal role in the emergence of plant parasitism in this phylum. Remarkably, we identify the first documented case of a plant-derived HGT in a nematode genome. This gene encodes a predicted secreted parasitic effector, underscoring the diversity of evolutionary events that contributed to the parasitic arsenal. Our results suggest that, beyond bacteria and fungi, plants themselves have provided crucial genes for parasitism that may now be used by the nematodes to manipulate them. Our comparative genomic analyses across more than 70 nematode species further uncover an unprecedented epigenetic toolkit in an invertebrate genome. Indeed, X. index harbors a complete set of canonical DNA methyltransferases, a full-length ATRX chromatin remodeler, and 3D-chromatin architectural CTCF protein coding homolog. Consistent with this repertoire, we detected methylation at CpG genome-wide, which inversely correlates with gene expression and chromatin accessibility. Together, these findings reveal a vertebrate-like epigenetic machinery in an early-branching nematode and call for a fundamental reassessment of the prevailing epigenetic paradigm in nematodes and, more broadly, in animals.

genomics↗

bioRxiv2024

Identification and Expression of the peach TNL RMia genes for the Resistance to the Root-knot Nematode Meloidogyne incognita

Root-Knot Nematodes (RKN) are major pests for world agriculture. As RKN are polyphagous endoparasites, present in various climates and able to multiply rapidly, the quest to discover new natural resistances in plants is essential. In Prunus species, several major resistance genes to RKN that belong to the NLR family, have been detected in recent years. In Peach, the RMia gene, which confers resistance to the RKN Meloidogyne incognita, M. arenaria, and M. ethiopica, was localized on the chromosome 2. In this study, we used short-and long-read sequencing technologies to identify the RMia gene in two independent RKN-resistant peach varieties. We characterized three candidate genes and studied their expression profile upon RKN infection. Our study identified and characterized these candidates that are most likely involved in the RKN resistance. Ultimately, we developed new molecular markers associated to this resistance that can be used in breeding programs.

plant biology↗

bioRxiv2023

Conifers concentrate large numbers of NLR immune receptor genes on one chromosome

Nucleotide-binding domain and Leucine-rich Repeat (NLR) immune receptor genes form a major line of defence in plants, acting in both pathogen recognition and resistance machinery activation. NLRs are reported to form large gene clusters in limber pine (Pinus flexilis) but it is unknown how widespread this genomic architecture may be among the extant species of conifers (Pinophyta). We used comparative genomic analyses to assess patterns in the abundance, diversity and genomic distribution of NLR genes. Chromosome-level whole genome assemblies and high-density linkage maps in the Pinaceae, Cupressaceae, Taxaceae and other gymnosperms were scanned for NLR genes using existing and customised pipelines. Discovered genes were mapped across chromosomes and linkage groups, and analysed phylogenetically for evolutionary history. Conifer genomes are characterised by dense clusters of NLR genes, highly localised on one chromosome. These clusters are rich in TNL-encoding genes, which seem to have formed through multiple tandem duplication events. In contrast to angiosperms and non-coniferous gymnosperms, genomic clustering of NLR genes is ubiquitous in conifers. NLR-dense genomic regions are likely to influence a large part of the plants resistance, informing our understanding of adaptation to biotic stress and the development of genetic resources through breeding. Plain language summaryNLR immune receptor genes are important in pest, disease and drought resistance of plants. In the giga-genomes of conifers, they concentrate on very small chromosomal regions. These regions act as important reservoirs for NLR diversity and can be used in breeding to improve the resilience of conifer trees.

genomics↗

bioRxiv2023

Genome sequence and annotation of Periconia digitata, a promising biocontrol agent of phytopathogenic oomycetes

The Periconia fungal genus belongs to the phylum Ascomycota, order Pleosporales, family Periconiaceae. Periconia are found in many habitats but little is known about their ecology. Several species from this genus produce bioactive molecules. Periconia digitata extracts were shown to be deadly active against the pine wilt nematode. Furthermore, P. digitata was shown to inhibit plant pathogenic oomycete Phytophthora parasitica. Because P. digitata has great potential as a biocontrol agent and high quality genomic resources are still lacking in the Periconiaceae family, we generated long-read genomic data for P. digitata. Using the PacBio Hifi sequencing technology, we obtained a highly-contiguous genome assembled in 13 chromosomes and totalling ca. 39 Mb. In addition, we produced a reference transcriptome, based on 12 different culture conditions, and proteomic data to support the genome annotation. Besides representing a new reference genome within the Periconiaceae, this work will contribute to our better understanding of the Eukaryotic tree of life and opens new possibilities in terms of biotechnological applications.

microbiology↗