Lax Gordon, Kwong Waldan K, Na Ina, Jacko-Reynolds Victoria K L, Trznadel Morelia, House Chloe S E, Mathur Varsha, Wakeman Kevin C, Keeling Patrick J
Department of Botany, University of British Columbia, Vancouver, Canada.
Department of Biology, Dalhousie University, Halifax, Canada.
Genome Biol Evol. 2025 May 30;17(6). doi: 10.1093/gbe/evaf117.
Apicomplexans are widespread and diverse obligate symbionts of animals, and many-like the malaria-causing Plasmodium-are important human parasites. Some of the closest free-living relatives of apicomplexans are photosynthetic, and most apicomplexans retain a relict, nonphotosynthetic plastid called the apicoplast. The origin and evolution of this plastid has been studied extensively, but most data come from biomedically relevant taxa. There has been increasing interest in the diversity of plastids of other apicomplexans, which has revealed a complex picture of recurring, independent losses of plastids or their genomes in the deepest-branching apicomplexan lineages, Cryptosporidium and the gregarines. Indeed, the plastid is absent from many of these deep-branching apicomplexans, and those that retain it have almost all lost its genome. The single exception appears to be the archigregarines, the deepest-branching subgroup of gregarines, which are suspected to have retained a genome based on analyses of nuclear genes, but for which no plastid genome data are known. As the best potential representatives of plastid genomes in deep-branching apicomplexans, this lineage is an obvious missing piece of the evolutionary puzzle of the apicoplast. Here, we used single-cell sequencing to characterize the plastid genome from uncultivated representatives of all 4 known archigregarine lineages. The plastid genomes are all more divergent with lower GC-content than other apicoplast genomes, and encode a slightly different set of genes. There is no evidence of photosynthesis-related genes. These genomes fill a key gap in the diversity of apicomplexan plastid genomes, furthering our understanding of the complex evolution of the apicoplast.
顶复门原虫是广泛存在且多样的动物专性共生体，许多顶复门原虫，如导致疟疾的疟原虫，都是重要的人体寄生虫。顶复门原虫一些关系最近的自由生活亲属是光合生物，并且大多数顶复门原虫保留了一种残余的、非光合的质体，称为顶质体。这种质体的起源和进化已得到广泛研究，但大多数数据来自与生物医学相关的类群。人们对其他顶复门原虫质体的多样性越来越感兴趣，这揭示了一个复杂的情况，即在最深分支的顶复门原虫谱系、隐孢子虫和簇虫中，质体或其基因组反复独立丢失。事实上，许多这些最深分支的顶复门原虫都没有质体，而那些保留质体的几乎都失去了其基因组。唯一的例外似乎是原簇虫，它是簇虫中最深分支的亚群，基于核基因分析怀疑其保留了基因组，但尚无质体基因组数据。作为最深分支顶复门原虫中质体基因组的最佳潜在代表，这个谱系显然是顶质体进化难题中缺失的一块。在这里，我们使用单细胞测序来表征所有4个已知原簇虫谱系未培养代表的质体基因组。这些质体基因组与其他顶质体基因组相比，GC含量更低，差异更大，并且编码的基因集略有不同。没有光合作用相关基因的证据。这些基因组填补了顶复门原虫质体基因组多样性中的一个关键空白，加深了我们对顶质体复杂进化的理解。
