Department of Horticulture, The University of Georgia, 2360 Rainwater Rd,, Tifton, GA 31793-5766, USA.
BMC Evol Biol. 2011 Oct 5;11:289. doi: 10.1186/1471-2148-11-289.
Apomixis is an intriguing trait in plants that results in maternal clones through seed reproduction. Apomixis is an elusive, but potentially revolutionary, trait for plant breeding and hybrid seed production. Recent studies arguing that apomicts are not evolutionary dead ends have generated further interest in the evolution of asexual flowering plants.
In the present study, we investigate karyotypic variation in a single chromosome responsible for transmitting apomixis, the Apospory-Specific Genomic Region carrier chromosome, in relation to species phylogeny in the genera Pennisetum and Cenchrus. A 1 kb region from the 3' end of the ndhF gene and a 900 bp region from trnL-F were sequenced from 12 apomictic and eight sexual species in the genus Pennisetum and allied genus Cenchrus. An 800 bp region from the Apospory-Specific Genomic Region also was sequenced from the 12 apomicts. Molecular cytological analysis was conducted in sixteen Pennisetum and two Cenchrus species. Our results indicate that the Apospory-Specific Genomic Region is shared by all apomictic species while it is absent from all sexual species or cytotypes. Contrary to our previous observations in Pennisetum squamulatum and Cenchrus ciliaris, retrotransposon sequences of the Opie-2-like family were not closely associated with the Apospory-Specific Genomic Region in all apomictic species, suggesting that they may have been accumulated after the Apospory-Specific Genomic Region originated.
Given that phylogenetic analysis merged Cenchrus and newly investigated Pennisetum species into a single clade containing a terminal cluster of Cenchrus apomicts, the presumed monophyletic origin of Cenchrus is supported. The Apospory-Specific Genomic Region likely preceded speciation in Cenchrus and its lateral transfer through hybridization and subsequent chromosome repatterning may have contributed to further speciation in the two genera.
无融合生殖是一种有趣的植物特性，它通过种子繁殖产生母本克隆。无融合生殖是植物育种和杂交种子生产中一种难以捉摸但具有潜在革命性的特性。最近的研究表明，无融合生殖的个体并不是进化的死胡同，这进一步激发了人们对无性开花植物进化的兴趣。
在本研究中，我们调查了负责传递无融合生殖的单个染色体——无融合生殖特异性基因组区域载体染色体——与雀稗属和蒺藜草属物种系统发育之间的核型变异。我们从雀稗属和相关蒺藜草属的 12 个无融合生殖和 8 个有性生殖物种中，从 ndhF 基因 3'端的 1kb 区域和 trnL-F 的 900bp 区域进行了测序。还从 12 个无融合生殖个体中测序了来自无融合生殖特异性基因组区域的 800bp 区域。在 16 个雀稗属和 2 个蒺藜草属物种中进行了分子细胞学分析。我们的结果表明，无融合生殖特异性基因组区域存在于所有无融合生殖物种中，而不存在于所有有性生殖物种或核型中。与我们之前在雀稗属 squamulatum 和蒺藜草属 ciliaris 中的观察结果相反，Opie-2 样家族的逆转座子序列与所有无融合生殖个体中的无融合生殖特异性基因组区域并不密切相关，这表明它们可能是在无融合生殖特异性基因组区域起源后积累的。
鉴于系统发育分析将蒺藜草属和新调查的雀稗属物种合并到一个单一的分支中，该分支包含蒺藜草属无融合生殖个体的末端聚类，因此支持蒺藜草属假定的单系起源。无融合生殖特异性基因组区域可能先于蒺藜草属的物种形成，通过杂交和随后的染色体重排进行的侧向转移可能促进了这两个属的进一步物种形成。
