PDF(Pubmed)
Abstract：
Dinoflagellates in the family Symbiodiniaceae are taxonomically diverse, predominantly symbiotic lineages that are well-known for their association with corals. The ancestor of these taxa is believed to have been free-living. The establishment of symbiosis (i.e. symbiogenesis) is hypothesized to have occurred multiple times during Symbiodiniaceae evolution, but its impact on genome evolution of these taxa is largely unknown. Among Symbiodiniaceae, the genus Effrenium is a free-living lineage that is phylogenetically positioned between two robustly supported groups of genera within which symbiotic taxa have emerged. The apparent lack of symbiogenesis in Effrenium suggests that the ancestral features of Symbiodiniaceae may have been retained in this lineage. Here, we present de novo assembled genomes (1.2-1.9 Gbp in size) and transcriptome data from three isolates of Effrenium voratum and conduct a comparative analysis that includes 16 Symbiodiniaceae taxa and the other dinoflagellates. Surprisingly, we find that genome reduction, which is often associated with a symbiotic lifestyle, predates the origin of Symbiodiniaceae. The free-living lifestyle distinguishes Effrenium from symbiotic Symbiodiniaceae vis-à-vis their longer introns, more-extensive mRNA editing, fewer (~30%) lineage-specific gene sets, and lower (~10%) level of pseudogenization. These results demonstrate how genome reduction and the adaptation to distinct lifestyles intersect to drive diversification and genome evolution of Symbiodiniaceae.
摘要：
共生菌科中的鞭毛藻在分类学上是多样的，主要是共生谱系，以与珊瑚的联系而闻名。这些类群的祖先被认为是自由生活的。共生关系的建立(即，共生体）被假设在共生菌科进化过程中发生了多次，但是它对这些分类群的基因组进化的影响在很大程度上是未知的。在共生虫科中，Effrenium属是一个自由生活的谱系，在系统发育上位于两个强烈支持的属群之间，其中出现了共生分类群。Effrenium中明显缺乏共生体，这表明该谱系中可能保留了共生体科的祖先特征。在这里，我们介绍了来自三个Effreniumvoratum分离株的从头组装基因组（大小为1.2-1.9Gbp）和转录组数据，并进行了比较分析，其中包括16个共生虫科类群和其他鞭毛藻。令人惊讶的是,我们发现基因组减少，这通常与共生的生活方式有关，早于共生菌科的起源。自由生活的生活方式将Effrenium与共生共生菌科相对于其更长的内含子区分开来，更广泛的mRNA编辑，更少的（〜30％）谱系特异性基因集，和较低(~10%)水平的假基因。这些结果表明，基因组减少和对不同生活方式的适应是如何相交的，以驱动共生科的多样化和基因组进化。
