Goulding S E, Olmstead R G, Morden C W, Wolfe K H
Department of Genetics, University of Dublin, Trinity College, Ireland.
Mol Gen Genet. 1996 Aug 27;252(1-2):195-206. doi: 10.1007/BF02173220.
The endpoints of the large inverted repeat (IR) of chloroplast DNA in flowering plants differ by small amounts between species. To quantify the extent of this movement and define a possible mechanism for IR expansion, DNA sequences across the IR-large single-copy (IR-LSC) junctions were compared among 13 Nicotiana species and other dicots. In most Nicotiana species the IR terminates just upstream of, or somewhere within, the 5' portion of the rps19 gene. The truncated copy of this gene, rps19', varies in length even between closely related species but is of constant size within a single species. In Nicotiana, six different rps19' structures were found. A phylogenetic tree of Nicotiana species based on restriction site data shows that the IR has both expanded and contracted during the evolution of this genus. Gene conversion is proposed to account for these small and apparently random IR expansions. A large IR expansion of over 12 kb has occurred in Nicotiana acuminata. The new IR-LSC junction in this species lies within intron 1 of the clpP gene. This rearrangement occurred via a double-strand DNA break and recombination between poly (A) tracts in clpP intron 1 and upstream of rps19. Nicotiana acuminata chloroplast DNA contains a "molecular fossil' of the IR-LSC junction that existed prior to this dramatic rearrangement.
开花植物叶绿体DNA的大反向重复序列（IR）的末端在不同物种之间存在少量差异。为了量化这种移动的程度并确定IR扩展的可能机制，我们比较了13种烟草属物种和其他双子叶植物中跨越IR-大单拷贝（IR-LSC）连接点的DNA序列。在大多数烟草属物种中，IR在rps19基因5'部分的上游或内部某处终止。该基因的截短拷贝rps19'，即使在亲缘关系密切的物种之间长度也有所不同，但在单个物种内大小恒定。在烟草属中，发现了六种不同的rps19'结构。基于限制性位点数据构建的烟草属物种系统发育树表明，在该属的进化过程中，IR既发生了扩展也发生了收缩。有人提出基因转换可以解释这些微小且明显随机的IR扩展。在尖叶烟草中发生了超过12 kb的大IR扩展。该物种新的IR-LSC连接点位于clpP基因的内含子1内。这种重排是通过clpP内含子1中的多聚（A）序列与rps19上游之间的双链DNA断裂和重组发生的。尖叶烟草叶绿体DNA包含了在这种剧烈重排之前存在的IR-LSC连接点的“分子化石”。
