Luthringer Rémy, Lipinska Agnieszka P, Roze Denis, Cormier Alexandre, Macaisne Nicolas, Peters Akira F, Cock J Mark, Coelho Susana M
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, Roscoff, France.
UMI 3614, Evolutionary Biology and Ecology of Algae, CNRS, Sorbonne Universités, UPMC, PUCCh, UACH, Station Biologique de Roscoff, Roscoff, France.
Mol Biol Evol. 2015 Nov;32(11):2973-85. doi: 10.1093/molbev/msv173. Epub 2015 Aug 6.
The recombining regions of sex chromosomes (pseudoautosomal regions, PARs) are predicted to exhibit unusual features due to their being genetically linked to the nonrecombining, sex-determining region. This phenomenon is expected to occur in both diploid (XY, ZW) and haploid (UV) sexual systems, with slightly different consequences for UV sexual systems because of the absence of masking during the haploid phase (when sex is expressed) and because there is no homozygous sex in these systems. Despite a considerable amount of theoretical work on PAR genetics and evolution, these genomic regions have remained poorly characterized empirically. We show here that although the PARs of the U/V sex chromosomes of the brown alga Ectocarpus recombine at a similar rate to autosomal regions of the genome, they exhibit many genomic features typical of nonrecombining regions. The PARs were enriched in clusters of genes that are preferentially, and often exclusively, expressed during the sporophyte generation of the life cycle, and many of these genes appear to have evolved since the Ectocarpales diverged from other brown algal lineages. A modeling-based approach was used to investigate possible evolutionary mechanisms underlying this enrichment in sporophyte-biased genes. Our results are consistent with the evolution of the PAR in haploid systems being influenced by differential selection pressures in males and females acting on alleles that are advantageous during the sporophyte generation of the life cycle.
性染色体的重组区域（假常染色体区域，PARs）由于与非重组的性别决定区域存在遗传联系，预计会呈现出不同寻常的特征。这种现象预计会在二倍体（XY、ZW）和单倍体（UV）性别系统中出现，对于UV性别系统而言，由于在单倍体阶段（即表达性别的阶段）不存在掩盖效应，且这些系统中不存在纯合性别，因此会产生略有不同的结果。尽管在PAR遗传学和进化方面已经开展了大量的理论研究，但这些基因组区域在实证研究中仍未得到充分表征。我们在此表明，尽管褐藻石莼的U/V性染色体的PARs与基因组的常染色体区域以相似的速率进行重组，但它们呈现出许多非重组区域典型的基因组特征。PARs富含在生命周期的孢子体世代中优先且通常仅表达的基因簇，并且其中许多基因似乎自水云目与其他褐藻谱系分化以来就已经进化。我们采用了基于模型的方法来研究这种孢子体偏向基因富集背后可能的进化机制。我们的结果与单倍体系统中PAR的进化受雄性和雌性在生命周期的孢子体世代中对有利等位基因施加的差异选择压力影响这一观点一致。
