Leslie, C. A. | Search bioRxiv

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

Extreme somatic mutation variation through time and space in walnut clones

Many plants, unlike most animals, can reproduce as clones1. Cloning plants is critical for agriculture2,3 and biotechnology4, but the extent of somatic mutation arising during different propagation methods remains an important question for both fundamental research and agriculture. Here, we discover a surprisingly complex mutational history in a multi-decade natural experiment of isogenic walnut clones derived and maintained through three alternative methods: budwood propagation of field-grown trees, in vitro shoot culturing, and in vitro somatic embryogenesis. We generated a haplotype-phased reference genome assembly and revealed a >3500% increase in somatic embryo mutation rates compared to field-grown trees, along with a distinct mutation spectrum. The assembly also helped reveal extreme genomic instability in the somatic embryos, including multiple chromosomal duplications, megabase-scale deletions, telomere expansions, somatic recombination events, and ongoing transposable element activation. Our survey of somatic mutation also provides high-resolution insight into clonal stem cell dynamics, confirming the canonical meristem layers of flowering plants in the tree and shoot clones, while uncovering clear evidence of frequent single-cell bottlenecks in the somatic embryos. These discoveries inform practical questions about mutagenesis through plant tissue culture and serve as a benchmark to complement emerging paradigms of somatic mutation research in humans and other organisms.

genomics↗