Zea mays Epigenomics. Zea mays

The ability of centromeres to alternate between active and inactive states indicates significant epigenetic elements controlling centromere assembly and centromere function. In maize (Zea mays), misdivision of the B chromosome centromere on a translocation with the short arm of chromosome 9 (TB-9Sb) can produce many variants with varying centromere sizes and centromeric DNA sequences. In derivatives of TB-9Sb, we found a de novo centromere on chromosome telo-3-3, which has no canonical centromeric repeat sequences. This centromere is derived from a 288-kb region on the short arm of chromosome 9, and is 19 megabases (Mb) removed from the translocation breakpoint of chromosome 9 in TB-9Sb. This centromere is much smaller than normal ones but can be maintained through meiosis. The functional B centromere in progenitor telo2-2 is deleted from telo3-3 but some B-repeat sequences remain. The de novo centromere of telo3-3 becomes inactive in three further derivatives with new centromeres being formed elsewhere on the chromosomes. One such de novo centromere contains only 200-kb CENH3 binding domain. This 200-kb centromere is located 3 Mb removed from the translocation breakpoint in a new location. The deleted B centromere in telo3-3 is activated in two derivatives. Our results suggest that de novo centromere formation is more common than previously thought and can persist on chromosomal fragments without a canonical centromere providing implications for karyotype evolution. Overall design: ChIP-seq was carried out with anti-CENH3 antibodies using material from young leaves with control, telo3-3 and its derivate.

着丝粒（centromere）能够在活跃与失活状态间交替切换，这表明存在调控着丝粒组装与功能的关键表观遗传元件。在玉米（Zea mays）中，与9号染色体短臂发生易位的B染色体着丝粒（TB-9Sb）发生错分裂时，可产生多种着丝粒大小及着丝粒DNA序列存在差异的变异株系。在TB-9Sb的衍生株系中，我们在telo-3-3染色体上发现了一个从头形成的着丝粒（de novo centromere），该着丝粒不包含经典的着丝粒重复序列。该从头形成的着丝粒源自9号染色体短臂上一段288千碱基（kb）的区域，与TB-9Sb中9号染色体的易位断点相距19兆碱基（Mb）。该着丝粒虽远小于常规着丝粒，却可通过减数分裂实现世代维持。亲本株系telo2-2中的功能性B染色体着丝粒在telo3-3中被删除，但仍保留了部分B重复序列。在三个额外的衍生株系中，telo3-3的从头形成着丝粒会失活，同时染色体上的其他位置会形成新的着丝粒。其中一个此类从头形成的着丝粒仅包含200千碱基的CENH3结合结构域（CENH3 binding domain）。这个200千碱基的着丝粒位于易位断点以外3兆碱基的全新区域内。在两个衍生株系中，telo3-3内被删除的B染色体着丝粒被重新激活。我们的研究结果表明，从头形成着丝粒的发生频率高于此前认知，且可在不携带经典着丝粒的染色体片段上稳定存续，这为核型进化研究提供了启示。实验设计概述：以幼叶组织为材料，使用抗CENH3抗体（anti-CENH3 antibodies）进行染色质免疫共沉淀测序（ChIP-seq），实验分组包括对照组、telo3-3株系及其衍生株系。