Comparative genomics has revealed common occurrences in karyotype evolution such as chromosomal end-to-end fusions and insertions of one chromosome into another near the centromere, as well as many cases of de novo centromeres that generate positional polymorphisms. However, how rearrangements such as dicentrics and acentrics persist without being destroyed or lost remains unclear. Here, we sought experimental evidence for the frequency and timeframe for inactivation and de novo formation of centromeres in maize (Zea mays). The pollen from plants with supernumerary B chromosomes was gamma-irradiated and then applied to normal maize silks of a line without B chromosomes. In ~8,000 first-generation seedlings, we found many B–A translocations, centromere expansions, and ring chromosomes. We also found many dicentric chromosomes, but a fraction of these show only a single primary constriction, which suggests inactivation of one centromere. Chromosomal fragments were found without canonical centromere sequences, revealing de novo centromere formation over unique sequences; these were validated by immunolocalization with Thr133-phosphorylated histone H2A, a marker of active centromeres, and chromatin immunoprecipitation-sequencing with the CENH3 antibody. These results illustrate the regular occurrence of centromere birth and death after chromosomal rearrangement during a narrow window of one to potentially only a few cell cycles for the rearranged chromosomes to be recognized in this experimental regime.

比较基因组学揭示了核型进化中的常见现象，例如染色体端到端融合和一条染色体在着丝粒附近插入另一条染色体，以及许多从头着丝粒产生位置多态性的情况。然而，双着丝粒和无着丝粒等重排如何持续存在而不被破坏或丢失仍不清楚。在这里，我们寻求玉米（ Zea mays ）着丝粒失活和从头形成的频率和时间范围的实验证据。来自具有多余 B 染色体的植物的花粉经过伽马射线照射，然后应用于不具有 B 染色体的品系的正常玉米花丝。在约 8,000 个第一代幼苗中，我们发现了许多 B-A 易位、着丝粒扩张和环状染色体。我们还发现了许多双着丝粒染色体，但其中一小部分仅显示出一个初级缢缩，这表明一个着丝粒失活。发现的染色体片段没有典型的着丝粒序列，揭示了独特序列上的从头形成着丝粒；这些结果通过使用 Thr133 磷酸化组蛋白 H2A（活性着丝粒标记）进行免疫定位以及使用 CENH3 抗体进行染色质免疫沉淀测序进行了验证。这些结果说明，在一个到可能只有几个细胞周期的狭窄窗口内，染色体重排后着丝粒的出生和死亡定期发生，以便在该实验方案中识别重排的染色体。