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首页> 外文期刊>BMC Genomics >De novo transcriptome profiling uncovers a drastic downregulation of photosynthesis upon nitrogen deprivation in the nonmodel green alga Botryosphaerella sudeticus
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De novo transcriptome profiling uncovers a drastic downregulation of photosynthesis upon nitrogen deprivation in the nonmodel green alga Botryosphaerella sudeticus

机译：从头转录组分析揭示了非模型绿藻中的厌氧葡萄孢菌氮缺乏后光合作用的急剧下调。

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Background Neutral lipid storage is enhanced by nitrogen deprivation (ND) in numbers of green microalgal species. However, little is known about the metabolic pathways whose transcription levels are most significantly altered following ND in green microalgae, especially the nonmodel species. Results To start gaining knowledge on this, we performed transcriptome profiling of the nonmodel green microalga Botryosphaerella sudeticus cells in response to ND. Transcriptome of B. sudeticus is de novo assembled based on millions of HiSEQ short sequence reads using CLC Genomics Workbench software. The resulting non-redundant ESTs are annotated based on the best hits generated from the BLASTX homology comparison against the “best” proteins in the model microalgae Chlamydomonas reinhardtii and Chlorella variabilis. By using a pathway-based approach according to KEGG databases, we show that ESTs encoding ribosomal proteins and photosynthetic functions are the most abundantly expressed ESTs in the rapidly growing B. sudeticus cells. We find that ESTs encoding photosynthetic function but not the ribosomal proteins are most drastically downregulated upon ND. Notably, ESTs encoding lipid metabolic pathways are not significantly upregulated. Further analyses indicate that chlorophyll content is markedly decreased by 3-fold and total lipid content is only slightly increased by 50%, consistent with the transcriptional profiling. On the other hand, carbon content and photosynthesis efficiency are only marginally decreased by 7% and 20%, respectively, indicating that photosynthesis is only slightly reduced upon drastic downregulation of photosynthetic ESTs and chlorophyll content upon ND. In addition, TAG content is found to be greatly increased by 50-fold, though total lipid content is only slightly increased by 1.5-fold. Conclusions Taken together, our results suggest that light-harvesting proteins and chlorophylls are in excess in B. sudeticus. Degradation of excess photosynthesis proteins is most likely a mechanism for recycling of nitrogen-rich molecules to synthesize new proteins for preparation of gametogenesis and zygospore formation in adaptation and survival upon ND. Furthermore, our analyses indicate that TAG accumulation is largely attributed to the modification of other pre-existing lipid molecules, rather than de novo synthesis. We propose that this is likely an evolutionarily conserved mechanism in many green microalgae species.
机译：背景技术中的绿色微藻物种中的氮缺乏（ND）增强了中性脂质的存储。然而，对于绿色微藻特别是非模型物种中ND后其转录水平最显着改变的代谢途径知之甚少。结果为了开始对此有所了解，我们对ND响应的非模型绿色微藻葡萄孢菌进行了转录组分析。使用CLC Genomics Workbench软件基于数百万个HiSEQ短序列读数从头开始组装s。sudeticus的转录组。根据与模型微藻莱茵衣藻和变异小球藻中“最佳”蛋白质的BLASTX同源性比较产生的最佳结果，对所得的非冗余EST进行注释。通过使用基于路径的方法，根据KEGG数据库，我们表明编码核糖体蛋白和光合功能的EST是快速增长的s。sudeticus细胞中表达最丰富的EST。我们发现，编码光合功能而不是核糖体蛋白的EST在ND时被大大下调。值得注意的是，编码脂质代谢途径的EST没有明显上调。进一步的分析表明，叶绿素含量显着降低了3倍，总脂质含量仅略微提高了50％，与转录谱一致。另一方面，碳含量和光合作用效率仅分别略微降低了7％和20％，这表明光合作用的ESTs急剧下调和ND处理时的叶绿素含量仅使光合作用略有降低。另外，尽管总脂质含量仅略微增加了1.5倍，但发现TAG含量却大大增加了50倍。结论综上所述，我们的结果表明s。sudeticus中的光捕获蛋白和叶绿素过量。过量的光合作用蛋白的降解最有可能是富氮分子再循环以合成新蛋白的机制，以制备配子体形成和合子孢子形成，从而适应ND和存活。此外，我们的分析表明，TAG积累在很大程度上归因于其他现有脂质分子的修饰，而不是从头合成。我们建议这可能是许多绿色微藻物种中进化上保守的机制。

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