Ilic Katica, SanMiguel Phillip J, Bennetzen Jeffrey L
Department of Biological Sciences, Purdue University, 201 South University, West Lafayette, IN 47907-2064, USA.
Proc Natl Acad Sci U S A. 2003 Oct 14;100(21):12265-70. doi: 10.1073/pnas.1434476100. Epub 2003 Oct 6.
The sequences of large insert clones containing genomic DNA that is orthologous to the maize adh1 region were obtained for sorghum, rice, and the adh1-homoeologous region of maize, a remnant of the tetraploid history of the Zea lineage. By using all four genomes, it was possible to describe the nature, timing, and lineages of most of the genic rearrangements that have differentiated this chromosome segment over the last 60 million years. The rice genome has been the most stable, sharing 11 orthologous genes with sorghum and exhibiting only one tandem duplication of a gene in this region. The lineage that gave rise to sorghum and maize acquired a two-gene insertion (containing the adh locus), whereas sorghum received two additional gene insertions after its divergence from a common ancestor with maize. The two homoeologous regions of maize have been particularly unstable, with complete or partial deletion of three genes from one segment and four genes from the other segment. As a result, the region now contains only one duplicated locus compared with the eight original loci that were present in each diploid progenitor. Deletion of these maize genes did not remove both copies of any locus. This study suggests that grass genomes are generally unstable in local genome organization and gene content, but that some lineages are much more unstable than others. Maize, probably because of its polyploid origin, has exhibited extensive gene loss so that it is now approaching a diploid state.
获得了高粱、水稻以及玉米adh1同源区域（玉米谱系四倍体历史的遗迹）中与玉米adh1区域直系同源的包含基因组DNA的大片段插入克隆的序列。通过使用所有这四个基因组，得以描述在过去6000万年中使该染色体片段产生分化的大多数基因重排的性质、时间和谱系。水稻基因组最为稳定，与高粱共享11个直系同源基因，并且在该区域仅表现出一个基因的串联重复。产生高粱和玉米的谱系获得了一个双基因插入（包含adh基因座），而高粱在与玉米的共同祖先分化后又获得了另外两个基因插入。玉米的两个同源区域尤其不稳定，一个片段中有三个基因完全或部分缺失，另一个片段中有四个基因缺失。结果，与每个二倍体祖先中存在的八个原始基因座相比，该区域现在仅包含一个重复的基因座。这些玉米基因的缺失并未去除任何基因座的两个拷贝。这项研究表明，禾本科植物基因组在局部基因组组织和基因含量方面通常不稳定，但有些谱系比其他谱系更不稳定。玉米可能由于其多倍体起源，已经出现了广泛的基因丢失，以至于现在正接近二倍体状态。
