Transgenerational chromosome repair in the asexual bdelloid rotifer Adineta vaga

Homologous recombination plays a fundamental role in the evolution of organisms. It serves as a DNA repair mechanism which, in sexual organisms, contributes to genetic diversity through the shuffling of alleles during meiosis. Here we investigate the two functions of homologous recombination in the bdelloid rotifer Adineta vaga , an ancient asexual species also known for its tolerance to extreme genotoxic stresses. Genomic analyses reveal that A. vaga retained meiotic recombination mechanisms, both for DNA repair and occurrence of spontaneous crossovers during oogenesis. Our study introduces a novel transgenerational DNA repair mechanism termed break-induced homologous extension repair (BIHER). BIHER operates on single DNA ends, enabling the repair of fragmented chromosomes. Our findings suggest that the BIHER mechanism, combined with a holocentric structure of chromosomes and a modified meiosis, constitutes a key adaptation for life in extreme environments. Identifying such a mechanism in bdelloid rotifers sheds a new light on the strategies that evolved to maintain genome structure in asexually reproducing species.