High-Resolution Physical Mapping in Pennisetum squamulatum Reveals Extensive Chromosomal Heteromorphism of the Genomic Region Associated with Apomixis1
High-Resolution Physical Mapping in Pennisetum squamulatum Reveals Extensive Chromosomal Heteromorphism of the Genomic Region Associated with Apomixis1
复制标题
狼尾草的高分辨率物理作图揭示了与无融合生殖1相关的基因组区域广泛的染色体异形性
作者：
Y. Akiyama;Joann Conner;S. Goel;D. Morishige;J. Mullet;W. Hanna;P. Ozias‐Akins
配子体无融合生殖是一种无性生殖，是染色体未减少的卵子孤雌生殖发育的结果。该性状导致产生具有母体基因型的胚胎，即后代是母体植物的克隆。该性状在农业上的应用可以成为通过常规和非常规育种方法进行作物改良的巨大工具。不幸的是，没有主要的作物是通过无融合生殖的，与野生近缘种间杂交还没有产生具有商业可行性的种质资源。虎尾草（Pennisetum squamulatum）是一种无孢子无融合体，通过回交将无融合基因转移到有性珍珠粟上。与无融合相关的12个分子标记共存于一个称为无孢子特异性基因组区（ASGR）的紧密连锁块中，其中一些标记已被证明在squamulatum多倍体基因组中是半合子的。这些标记的高分辨率遗传作图是不可能的，因为在基因组的这个区域的低重组。我们现在用高分辨率荧光原位杂交技术在粗线染色体上展示了含有无融合连锁分子标记的细菌人工染色体的物理排列。ASGR的大小，目前被定义为与无融合连接的细菌人工染色体杂交的整个半合子区域，在粗线染色体和有丝分裂染色体上估计约为50 Mbp（染色体的四分之一）。ASGR包括来自opie -2样反转录转座子家族的高度重复序列，这些序列在基因组的这一区域尤其丰富。
Gametophytic apomixis is asexual reproduction as a consequence of parthenogenetic development of a chromosomally unreduced egg. The trait leads to the production of embryos with a maternal genotype, i.e. progeny are clones of the maternal plant. The application of the trait in agriculture could be a tremendous tool for crop improvement through conventional and nonconventional breeding methods. Unfortunately, there are no major crops that reproduce by apomixis, and interspecific hybridization with wild relatives has not yet resulted in commercially viable germplasm. Pennisetum squamulatum is an aposporous apomict from which the gene(s) for apomixis has been transferred to sexual pearl millet by backcrossing. Twelve molecular markers that are linked with apomixis coexist in a tight linkage block called the apospory-specific genomic region (ASGR), and several of these markers have been shown to be hemizygous in the polyploid genome of P. squamulatum. High resolution genetic mapping of these markers has not been possible because of low recombination in this region of the genome. We now show the physical arrangement of bacterial artificial chromosomes containing apomixis-linked molecular markers by high resolution fluorescence in situ hybridization on pachytene chromosomes. The size of the ASGR, currently defined as the entire hemizygous region that hybridizes with apomixis-linked bacterial artificial chromosomes, was estimated on pachytene and mitotic chromosomes to be approximately 50 Mbp (a quarter of the chromosome). The ASGR includes highly repetitive sequences from an Opie-2-like retrotransposon family that are particularly abundant in this region of the genome.