Aligning Physical and Functional Maps of a Genomic Region Spanning the Apomixis Locus by Exploiting Model Cereal Genomics

无融合生殖是指通过种子进行无性生殖，在被子植物科中广泛存在，尽管75%的无融合生殖物种存在于禾本科、蔷薇科和菊科三个植物科中。本提案中研究的植物材料是禾本科的成员，这是人类食物链中最重要的作物植物家族。尽管玉米、小麦和珍珠粟的野生近缘种可能进行无性繁殖（无生殖），但该科的所有作物都是有性繁殖的。在无融合植物上形成的种子含有遗传上相同的胚胎，因此该性状在高产作物基因型中具有从一代到下一代保持杂交活力的显著潜力。鳞狼尾草和毛毛狼尾草减数分裂的典型现象是流产和未减少的无孢子胚囊从珠心细胞形成。狼尾草的遗传作图研究表明，形成未减少胚囊的位点位于染色体区域，重组率低。基于遗传图谱信息，对狼尾草无融合生殖相关基因进行了定位克隆。转录作图将使用已经开发的用于该区域物理作图的工具，也将使用相关二倍体模式物种（如高粱和水稻）的良好开发的分子工具。在这一区域探索两个模式二倍体和两个无融合物种之间的共线性将集中在高度保守的基因序列上。该区域的候选生殖基因或新基因将比较其在无融合和有性基因型/物种中的表达谱。本研究将为小基因组禾本科植物基因组信息向大基因组禾本科植物非重组区转移提供一个范例。

Apomixis, defined as asexual reproduction through seed, is widespread among angiosperm families although 75% of the apomictic species are found in three plant families, Poaceae, Rosaceae, and Asteraceae. The plant materials examined in this proposal are members of the Poaceae family, the most important crop plant family in the human food chain. All crop plants in this family reproduce sexually, although wild relatives of maize, wheat, and pearl millet may undergo asexual (apomictic) reproduction. Seeds formed on an apomictic plant contain genetically identical embryos, thus the trait has significant potential for preserving hybrid vigor from one generation to the next in highly productive crop plant genotypes. In Pennisetum squamulatum and Cenchrus ciliaris meiosis typically aborts and unreduced aposporous embryo sacs form from nucellar cells. Genetic mapping studies in Pennisetum have revealed that the locus for the formation of unreduced embryo sacs resides in a chromosomal region with a low recombination rate. Based on genetic map information, positional cloning of gene(s) responsible for apomictic reproduction in Pennisetum is in progress. Transcriptional mapping will use the tools that have been developed for physical mapping of this region and will also use the well developed molecular tools from related diploid model species such as sorghum and rice. The exploration of colinearity in this region between two model diploids and two apomictic species will focus on highly conserved gene sequences. Candidate reproductive or novel genes in this region will be compared for their expression profiles among apomictic and sexual genotypes/species. This research will provide an example of the transfer of genomic information from small-genome grasses to non-recombining regions of large-genome species.