Hypermutability of integrated sequences of viral origin in a chlorarachniophyte

• 成果类型: Article
• 署名作者: Mettrop, Lisa; Lipzen, Anna; Mirambeau, Gilles; Barry, Kerrie; Grigoriev, Igor V.; Piganeau, Gwenael; Krasovec, Marc
• 署名单位: Sorbonne Universite; United States Department of Energy (DOE); Joint Genome Institute - JGI; Lawrence Berkeley National Laboratory; University of California System; University of California Berkeley
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2612999123
• 发表日期: 2026-08-04
• 页码: e2612999123
• 关键词: spontaneous mutation; mutation rate; Bigelowiella natans; virus; genome integrity; spontaneous mutations; dna; genomes; EVOLUTION; spectrum; inosine; rates

摘要

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 found extreme local variation in mutation rate: over 1,000-fold differences across its nuclear genome. While the baseline single-nucleotide mutation rate is approximately 3.5 & times; 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 & times; 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.