Interchromosomal Translocations and Large Deletions Drive the Evolution of the Outlier Chromosome in the Smallest Photosynthetic Eukaryote
Abstract
Marine microalgal populations can rapidly evolve resistance to viruses upon infection. In Ostreococcus mediterraneus, resistance to the prasinovirus OmV2 emerged within 5 d in all virus-exposed populations. Whole-genome sequencing of pairs of resistant and susceptible cell lines revealed extensive structural genomic changes, particularly on the small outlier chromosome (SOC). SOC alterations included large deletions, duplications, rearrangements, and wholechromosome duplication, yet no consistent structural variant or single nucleotide polymorphism was directly associated with resistance. Hybrid de novo assemblies confirmed the unique SOC assembly of each strain, with a highly polymorphic ∼2 kb tandem repeat region exhibiting an "accordion-like" pattern of expansion and contraction. No new viral insertions were found, though endogenous viral elements were conserved across lines. Two interchromosomal translocations between the SOC and chromosomes 2 and 17 offer novel insights into the mechanisms underlying the distinctive evolutionary path of this chromosome. Together, these findings demonstrate that resistance to OmV2 evolves rapidly and consistently but cannot yet be attributed to any specific structural variations, suggesting that transcriptional or posttranscriptional mechanisms underlie the resistant phenotype. Instead, the high rate of localized genomic structural variations points to a distinct mechanism of chromosome evolution.
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BibTeX
@article{bugnot2026interchromosomal,
title = {{Interchromosomal Translocations and Large Deletions Drive the Evolution of the Outlier Chromosome in the Smallest Photosynthetic Eukaryote}},
author = {Claire Bugnot and Tyler Alioto and Fernando Cruz and Eric Manirakiza and Jessica Gomez Garrido and Marta Gut and Sheree Yau and Gwenael Piganeau},
journal = {Genome Biology and Evolution},
year = {2026},
month = jul,
doi = {10.1093/gbe/evag162},
url = {https://hal.science/hal-05777119v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Interchromosomal Translocations and Large Deletions Drive the Evolution of the Outlier Chromosome in the Smallest Photosynthetic Eukaryote
AU - Claire Bugnot
AU - Tyler Alioto
AU - Fernando Cruz
AU - Eric Manirakiza
AU - Jessica Gomez Garrido
AU - Marta Gut
AU - Sheree Yau
AU - Gwenael Piganeau
PY - 2026
DA - 2026/07/02
JO - Genome Biology and Evolution
DO - 10.1093/gbe/evag162
UR - https://hal.science/hal-05777119v1
AB - Marine microalgal populations can rapidly evolve resistance to viruses upon infection. In Ostreococcus mediterraneus, resistance to the prasinovirus OmV2 emerged within 5 d in all virus-exposed populations. Whole-genome sequencing of pairs of resistant and susceptible cell lines revealed extensive structural genomic changes, particularly on the small outlier chromosome (SOC). SOC alterations included large deletions, duplications, rearrangements, and wholechromosome duplication, yet no consistent structural variant or single nucleotide polymorphism was directly associated with resistance. Hybrid de novo assemblies confirmed the unique SOC assembly of each strain, with a highly polymorphic ∼2 kb tandem repeat region exhibiting an "accordion-like" pattern of expansion and contraction. No new viral insertions were found, though endogenous viral elements were conserved across lines. Two interchromosomal translocations between the SOC and chromosomes 2 and 17 offer novel insights into the mechanisms underlying the distinctive evolutionary path of this chromosome. Together, these findings demonstrate that resistance to OmV2 evolves rapidly and consistently but cannot yet be attributed to any specific structural variations, suggesting that transcriptional or posttranscriptional mechanisms underlie the resistant phenotype. Instead, the high rate of localized genomic structural variations points to a distinct mechanism of chromosome evolution.
SN - 1759-6653
SN - 1759-6653
ER -