Toso Marc A, Omoto Charlotte K
School of Biological Sciences, Washington State University, Pullman, Washington 99164-4236, USA.
J Eukaryot Microbiol. 2007 Jan-Feb;54(1):66-72. doi: 10.1111/j.1550-7408.2006.00229.x.
Gregarines are early diverging apicomplexans that appear to be closely related to Cryptosporidium. Most apicomplexans, including Plasmodium, Toxoplasma, and Eimeria, possess both plastids and corresponding plastid genomes. Cryptosporidium lacks both the organelle and the genome. To investigate the evolutionary history of plastids in the Apicomplexa, we tried to determine whether gregarines possess a plastid and/or its genome. We used PCR and dot-blot hybridization to determine whether the gregarine Gregarina niphandrodes possesses a plastid genome. We used an inhibitor of plastid function for any reduction in gregarine infection, and transmission electron microscopy to search for plastid ultrastructure. Despite an extensive search, an organelle of the appropriate ultrastructure in transmission electron microscopy, was not observed. Triclosan, an inhibitor of the plastid-specific enoyl-acyl carrier reductase enzyme, did not reduce host infection by G. niphandrodes. Plastid-specific primers produced amplicons with the DNA of Babesia equi, Plasmodium falciparum, and Toxoplasma gondii as templates, but not with G. niphandrodes DNA. Plastid-specific DNA probes, which hybridized to Babesia equi, failed to hybridize to G. niphandrodes DNA. This evidence indicates that G. niphandrodes is not likely to possess either a plastid organelle or its genome. This raises the possibility that the plastid was lost in the Apicomplexan following the divergence of gregarines and Cryptosporidium.
簇虫是早期分化的顶复门原虫，似乎与隐孢子虫关系密切。大多数顶复门原虫，包括疟原虫、弓形虫和艾美耳球虫，都拥有质体和相应的质体基因组。隐孢子虫既缺乏这种细胞器，也没有该基因组。为了研究顶复门原虫中质体的进化历史，我们试图确定簇虫是否拥有质体和/或其基因组。我们使用聚合酶链式反应（PCR）和斑点杂交来确定簇虫尼氏嗜簇虫是否拥有质体基因组。我们使用质体功能抑制剂来观察簇虫感染率是否降低，并利用透射电子显微镜来寻找质体超微结构。尽管进行了广泛的搜索，但在透射电子显微镜下未观察到具有合适超微结构的细胞器。三氯生是一种质体特异性烯酰 - 酰基载体还原酶的抑制剂，它并没有降低尼氏嗜簇虫对宿主的感染率。以质体特异性引物分别以马巴贝斯虫、恶性疟原虫和刚地弓形虫的DNA为模板能产生扩增子，但以尼氏嗜簇虫的DNA为模板则不能。与马巴贝斯虫杂交的质体特异性DNA探针未能与尼氏嗜簇虫的DNA杂交。这些证据表明，尼氏嗜簇虫不太可能拥有质体细胞器或其基因组。这就增加了一种可能性，即在簇虫和隐孢子虫分化之后，质体在顶复门原虫中丢失了。
