Sousa Aretuza, Fuchs Jörg, Renner Susanne S
Department of Biology, University of Munich (LMU), 80638, Munich, Germany.
Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Gatersleben, 06466, Stadt Seeland, Germany.
Chromosome Res. 2017 Jun;25(2):191-200. doi: 10.1007/s10577-017-9555-y. Epub 2017 Mar 25.
Our understanding of the evolution of plant sex chromosomes is increasing rapidly due to high-throughput sequencing data and phylogenetic and molecular-cytogenetic approaches that make it possible to infer the evolutionary direction and steps leading from homomorphic to heteromorphic sex chromosomes. Here, we focus on four species of Coccinia, a genus of 25 dioecious species, including Coccinia grandis, the species with the largest known plant Y chromosome. Based on a phylogeny for the genus, we selected three species close to C. grandis to test the distribution of eight repetitive elements including two satellites, and several plastid and mitochondrial probes, that we had previously found to have distinct accumulation patterns in the C. grandis genome. Additionally, we determined C-values and performed immunostaining experiments with (peri-)centromere-specific antibodies on two species (for comparison with C. grandis). In spite of no microscopic chromosomal heteromorphism, single pairs of chromosomes in male cells of all three species accumulate some of the very same repeats that are enriched on the C. grandis Y chromosome, pointing to either old (previous) sex chromosomes or incipient (newly arising) ones, that is, to sex chromosome turnover. A 144-bp centromeric satellite repeat (CgCent) that characterizes all C. grandis chromosomes except the Y is highly abundant in all centromeric regions of the other species, indicating that the centromeric sequence of the Y chromosome diverged very recently.
由于高通量测序数据以及系统发育和分子细胞遗传学方法的出现，我们对植物性染色体进化的理解正在迅速增加，这些方法使得推断从同型性染色体到异型性染色体的进化方向和步骤成为可能。在这里，我们聚焦于南瓜属的四个物种，该属有25个雌雄异株物种，包括已知拥有最大植物Y染色体的大果栝楼。基于该属的系统发育，我们选择了三个与大果栝楼亲缘关系较近的物种，来测试包括两个卫星序列以及几个质体和线粒体探针在内的八个重复元件的分布情况，我们之前发现这些元件在大果栝楼基因组中有不同的积累模式。此外，我们测定了C值，并对两个物种（以便与大果栝楼进行比较）进行了用（近）着丝粒特异性抗体的免疫染色实验。尽管没有显微镜下的染色体异形性，但所有这三个物种雄性细胞中的单对染色体积累了一些与大果栝楼Y染色体上富集的完全相同的重复序列，这表明要么是古老的（先前的）性染色体，要么是初始的（新出现的）性染色体，也就是说，存在性染色体更替。一种144碱基对的着丝粒卫星重复序列（CgCent），它表征了除Y染色体外的所有大果栝楼染色体，在其他物种的所有着丝粒区域都高度丰富，这表明Y染色体的着丝粒序列最近才发生分歧。
