Hypermutability of integrated sequences of viral origin in a Chlorarachniophyte
Abstract
Mutations provide the raw material for evolution, but mutation rates are not uniform across genomes. Using a mutation accumulation experiment in the marine phytoplankton Bigelowiella natans, we discovered extreme local variation in mutation rate: over 1000-fold differences across its nuclear genome. While the baseline single-nucleotide mutation rate is approximately 3.5×10⁻¹⁰ per site per generation, a common value for unicellular species, two genomic regions derived from integrated viruses exhibit strikingly elevated rates of about 6×10⁻⁷. These two regions show a distinctive mutational signature with almost exclusively T/A→C/G transitions, a pattern also found in other non-eukaryote derived sequences in B. natans, contrary to the usual GC to AT mutation bias. Notably, hypermutation occurs only on TpA dinucleotides, and only in a subset of experimental lines, suggesting a regulated process rather than random genomic instability. We propose that B. natans targets invading DNA through localized hypermutation, reminiscent of deamination-based antiviral defense systems in animals. This prompts the idea of genome editing as a recurring immune strategy in eukaryotes.e viral genome increases its mutation rate to the point that the virus loses infectivity.
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BibTeX
@article{mettrop2026hypermutability,
title = {{Hypermutability of integrated sequences of viral origin in a Chlorarachniophyte}},
author = {Lisa Mettrop and Anna Lipzen and Gilles Mirambeau and Kerrie Barry and Igor Grigoriev and Gwenaël Piganeau and Marc Krasovec},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
year = {2026},
month = jul,
doi = {10.1073/pnas.2612999123},
url = {https://hal.science/hal-05748524v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Hypermutability of integrated sequences of viral origin in a Chlorarachniophyte
AU - Lisa Mettrop
AU - Anna Lipzen
AU - Gilles Mirambeau
AU - Kerrie Barry
AU - Igor Grigoriev
AU - Gwenaël Piganeau
AU - Marc Krasovec
PY - 2026
DA - 2026/07/28
JO - Proceedings of the National Academy of Sciences of the United States of America
DO - 10.1073/pnas.2612999123
UR - https://hal.science/hal-05748524v1
AB - Mutations provide the raw material for evolution, but mutation rates are not uniform across genomes. Using a mutation accumulation experiment in the marine phytoplankton Bigelowiella natans, we discovered extreme local variation in mutation rate: over 1000-fold differences across its nuclear genome. While the baseline single-nucleotide mutation rate is approximately 3.5×10⁻¹⁰ per site per generation, a common value for unicellular species, two genomic regions derived from integrated viruses exhibit strikingly elevated rates of about 6×10⁻⁷. These two regions show a distinctive mutational signature with almost exclusively T/A→C/G transitions, a pattern also found in other non-eukaryote derived sequences in B. natans, contrary to the usual GC to AT mutation bias. Notably, hypermutation occurs only on TpA dinucleotides, and only in a subset of experimental lines, suggesting a regulated process rather than random genomic instability. We propose that B. natans targets invading DNA through localized hypermutation, reminiscent of deamination-based antiviral defense systems in animals. This prompts the idea of genome editing as a recurring immune strategy in eukaryotes.e viral genome increases its mutation rate to the point that the virus loses infectivity.
SN - 0027-8424
SN - 1091-6490
ER -