Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada.
Mol Biol Evol. 2013 Nov;30(11):2447-62. doi: 10.1093/molbev/mst144. Epub 2013 Aug 22.
The canonical photosynthetic plastid genomes consist of a single circular-mapping chromosome that encodes a highly conserved protein core, involved in photosynthesis and ATP generation. Here, we demonstrate that the plastid genome of the photosynthetic relative of apicomplexans, Chromera velia, departs from this view in several unique ways. Core photosynthesis proteins PsaA and AtpB have been broken into two fragments, which we show are independently transcribed, oligoU-tailed, translated, and assembled into functional photosystem I and ATP synthase complexes. Genome-wide transcription profiles support expression of many other highly modified proteins, including several that contain extensions amounting to hundreds of amino acids in length. Canonical gene clusters and operons have been fragmented and reshuffled into novel putative transcriptional units. Massive genomic coverage by paired-end reads, coupled with pulsed-field gel electrophoresis and polymerase chain reaction, consistently indicate that the C. velia plastid genome is linear-mapping, a unique state among all plastids. Abundant intragenomic duplication probably mediated by recombination can explain protein splits, extensions, and genome linearization and is perhaps the key driving force behind the many features that defy the conventional ways of plastid genome architecture and function.
经典的光合质体基因组由一个单一的圆形图谱染色体组成，该染色体编码一个高度保守的蛋白质核心，参与光合作用和 ATP 生成。在这里，我们证明了光合质体相对类锥体的质体基因组在几个独特的方面偏离了这一观点。核心光合作用蛋白 PsaA 和 AtpB 已被分成两个片段，我们表明这些片段是独立转录的，带有寡 U 尾巴，翻译后组装成功能的光系统 I 和 ATP 合酶复合物。全基因组转录谱支持许多其他高度修饰蛋白的表达，包括几个包含数百个氨基酸长度的延伸的蛋白。经典的基因簇和操纵子已被分割和重新排列成新的假定转录单元。通过配对末端读取的大规模基因组覆盖，加上脉冲场凝胶电泳和聚合酶链反应，一致表明 C. velia 质体基因组是线性图谱，这在所有质体中是独特的状态。大量的基因组内重复可能是由重组介导的，这可以解释蛋白的分裂、延伸以及基因组的线性化，并且可能是许多违反质体基因组结构和功能的常规方式的特征的关键驱动力。
