Departments of Botany and Molecular and Population Genetics, University of Georgia, Athens, Georgia 30602.
Genetics. 1984 Mar;106(3):449-61. doi: 10.1093/genetics/106.3.449.
The evolution of specific regions of the chloroplast genome was studied in five grass species in the genus Pennisetum, including pearl millet, and one species from a related genus (Cenchrus). Three different regions of the chloroplast DNA were investigated. The first region included a 12-kilobase pair (kbp) EcoRI fragment containing the 23S, 16S and 5S ribosomal RNA genes, which is part of a larger duplicated region of reverse orientation. The second region was contained in a 21-kbp Sa/I fragment, which spans the short single-copy sequence separating the two reverse repeat structures and which overlaps the duplicated copies of the 12-kbp Eco RI fragment. The third region was a 6-kbp EcoRI fragment located in the large single-copy region of the chloroplast genome. Together these regions account for slightly less than 25% of the chloroplast genome. Each of these DNA fragments was cloned and used as hybridization probes to determine the distribution of homologous DNA fragments generated by various restriction endonuclease digests.-A survey of 12 geographically diverse collections of pearl millet showed no indication of chloroplast DNA sequence polymorphism, despite moderate levels of nuclear-encoded enzyme polymorphism. Interspecific and intergeneric differences were found for restriction endonuclease sites in both the small and the large single-copy regions of the chloroplast genome. The reverse repeat structure showed identical restriction site distributions in all materials surveyed. These results suggest that the reverse repeat region is differentially conserved during the evolution of the chloroplast genome.
研究了 5 种黍属植物（包括珍珠粟）和 1 种亲缘属植物（Cenchrus）的叶绿体基因组特定区域的进化。调查了叶绿体 DNA 的三个不同区域。第一个区域包括一个 12 千碱基对（kbp）的 EcoRI 片段，其中包含 23S、16S 和 5S 核糖体 RNA 基因，这是反向重复较大区域的一部分。第二个区域位于 21 kbp 的 Sa/I 片段中，跨越分离两个反向重复结构的短单拷贝序列，并与 12 kbp EcoRI 片段的重复拷贝重叠。第三个区域是位于叶绿体基因组大单拷贝区的 6 kbp EcoRI 片段。这些区域加起来略小于叶绿体基因组的 25%。这些 DNA 片段都被克隆并用作杂交探针，以确定不同限制内切酶消化产生的同源 DNA 片段的分布。对 12 个来自不同地理区域的珍珠粟收集品的调查表明，尽管核编码酶多态性处于中等水平，但没有叶绿体 DNA 序列多态性的迹象。在叶绿体基因组的小单拷贝区和大单拷贝区的限制内切酶位点都发现了种间和属间的差异。反向重复结构在所有调查材料中显示出相同的限制位点分布。这些结果表明，在叶绿体基因组的进化过程中，反向重复区是有差异的保守区。
