Smith David Roy, Lee Robert W
Department of Biology, University of Western Ontario, London, Ontario, Canada N6A 5B7.
Plant Physiol. 2014 Apr;164(4):1812-9. doi: 10.1104/pp.113.233718. Epub 2014 Feb 21.
Polytomella spp. are free-living, nonphotosynthetic green algae closely related to the model organism Chlamydomonas reinhardtii. Although colorless, Polytomella spp. have a plastid, but it is still unknown whether they harbor a plastid genome. We took a next generation sequencing approach, along with transcriptome sequencing, to search for a plastid genome and an associated gene expression system in Polytomella spp. Illumina sequencing of total DNA from four Polytomella spp. did not produce any recognizable plastid-derived reads but did generate a large number of mitochondrial DNA sequences. Transcriptomic analysis of Polytomella parva uncovered hundreds of putative nuclear-encoded, plastid-targeted proteins, which support the presence of plastid-based metabolic functions, similar to those observed in the plastids of other nonphotosynthetic algae. Conspicuously absent, however, were any plastid-targeted proteins involved in the expression, replication, or repair of plastid DNA. Based on these findings and earlier findings, we argue that the Polytomella genus represents the first well-supported example, to our knowledge, of a primary plastid-bearing lineage without a plastid genome.
多聚鞭毛虫属（Polytomella spp.）是与模式生物莱茵衣藻（Chlamydomonas reinhardtii）密切相关的自由生活的非光合绿藻。尽管多聚鞭毛虫属无色，但它有一个质体，不过其是否含有质体基因组仍不清楚。我们采用了下一代测序方法，并结合转录组测序，来寻找多聚鞭毛虫属中的质体基因组和相关的基因表达系统。对四种多聚鞭毛虫属的总DNA进行Illumina测序，未产生任何可识别的源自质体的读数，但确实产生了大量线粒体DNA序列。对微小多聚鞭毛虫（Polytomella parva）的转录组分析发现了数百种推测的核编码、靶向质体的蛋白质，这支持了基于质体的代谢功能的存在，类似于在其他非光合藻类的质体中观察到的情况。然而，明显缺乏的是任何参与质体DNA表达、复制或修复的靶向质体的蛋白质。基于这些发现和早期的发现，我们认为，据我们所知，多聚鞭毛虫属代表了第一个有充分证据支持的例子，即一个具有初级质体的谱系却没有质体基因组。
