Multiple metabolic roles for the nonphotosynthetic plastid of the green alga Prototheca wickerhamii
Multiple metabolic roles for the nonphotosynthetic plastid of the green alga Prototheca wickerhamii
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DOI：
10.1128/ec.4.2.253-261.2005
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发表时间：
2005-02-01
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影响因子：
--
通讯作者：
Lee, RW
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文献类型：
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作者：
Borza, T;Popescu, CE;Lee, RW
有充分证据表明，在失去光合作用能力的多种真核细胞谱系中存在质体。然而，这些细胞器的代谢功能知之甚少，除了顶复门（Apicomplexa）中的顶质体，一组细胞内寄生虫，包括恶性疟原虫（Plasmodium falciparum）和绿色螺旋孢子虫属（Helicosporidium sp.）的质体，到目前为止，自然界中唯一确定的无宿主阶段是以孢囊为代表的寄生虫。作为在非光合作用，主要是自由生活的生物体的质体功能重建的第一步，我们寻找表达序列标签（EST），对应于核编码的质体靶向多肽的绿色无绿藻wickerhamii。从3，856个EST中，我们发现71个独特的序列（235个EST）对应于不同的核编码的叶绿体靶向多肽。这些蛋白质预测了维氏原杆菌质体中的碳水化合物、氨基酸、脂质、四吡咯和类异戊二烯代谢以及嘌呤的从头合成和氧化还原过程。镁-原卟啉积累，因此，质体到细胞核的信号也可能发生在这个非光合生物，因为我们确定了一个转录本编码亚基I的镁螯合酶，催化叶绿素合成的第一个承诺的步骤的酶。我们的数据表明，一个更复杂的代谢在P. wickerhamii的质体的代谢途径相比，预测将位于恶性疟原虫的顶质体和螺旋孢子虫属的质体。
The presence of plastids in diverse eukaryotic lineages that have lost the capacity for photosynthesis is well documented. The metabolic functions of such organelles, however, are poorly understood except in the case of the apicoplast in the Apicomplexa, a group of intracellular parasites including Plasmodium falciparum, and the plastid of the green alga Helicosporidium sp., a parasite for which the only host-free stage identified in nature so far is represented by cysts. As a first step in the reconstruction of plastid functions in a nonphotosynthetic, predominantly free-living organism, we searched for expressed sequence tags (ESTs) that correspond to nucleus-encoded plastid-targeted polypeptides in the green alga Prototheca wickerhamii. From 3,856 ESTs, we found that 71 unique sequences (235 ESTs) correspond to different nucleus-encoded putatively plastid-targeted polypeptides. The identified proteins predict that carbohydrate, amino acid, lipid, tetrapyrrole, and isoprenoid metabolism as well as de novo purine biosynthesis and oxidoreductive processes take place in the plastid of P. wickerhamii. Mg-protoporphyrin accumulation and, therefore, plastid-to-nucleus signaling might also occur in this nonphotosynthetic organism, as we identified a transcript which encodes subunit I of Mg-chelatase, the enzyme which catalyzes the first committed step in chlorophyll synthesis. Our data indicate a far more complex metabolism in P. wickerhamii's plastid compared with the metabolic pathways predicted to be located in the apicoplast of P. falciparum and the plastid of Helicosporidium sp.