Haematococcus pluvialis could accumulate large amounts of triacylglycerol (TAG) and astaxanthin under various environmental stresses. To gain insights into the multiple defensive systems for carbon metabolism against nitrogen starvation, transcriptome analysis was performed. It was found that the genes related to carbon fixation, glycolysis, fatty acid and carotenoid biosynthesis pathways were up-regulated remarkably. Glyceraldehyde 3-phosphate (G3P) biosynthesis was accelerated with the enhanced C3 and C4 pathway. Meanwhile, the pyruvate kinase (PK) and pyruvate dehydrogenase E2 component (aceF) genes were significantly increased 12.9-fold and 13.9-fold, respectively, resulting more pyruvate and acetyl-CoA generation, which were beneficial to carotenoids and fatty acid biosynthesis. Methylerythritol 4-phosphate (MEP) pathway mediated carotenoid precursor isopentenyl diphosphate (IPP) synthesis, as the all eight related genes were up-regulated. The carbon flux toward astaxanthin biosynthesis with the increased astaxanthin pathway genes. The redistribution of carbon was also promoted for TAG accumulation. In addition, the up-regulation of diacylglycerol acyltransferase (DGAT) and phospholipid: diacylglycerol acyltransferase (PDAT) genes indicated that both acyl-CoA dependent and independent pathway regulated TAG accumulation. Therefore, this work reveals the multiple defensive mechanism for carbon metabolism in response to nitrogen starvation, which extended our understanding on the carotenoids, TAG and other important metabolites synthesis.

中文翻译：

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雨生红球藻抗氮饥饿多种防御系统的转录组分析

雨生红球藻可以在各种环境胁迫下积累大量的三酰甘油（TAG）和虾青素。为了深入了解针对氮饥饿的碳代谢的多重防御系统，进行了转录组分析。发现与碳固定、糖酵解、脂肪酸和类胡萝卜素生物合成途径相关的基因显着上调。甘油醛 3-磷酸 (G3P) 生物合成通过增强的 C3 和 C4 途径加速。同时，丙酮酸激酶 (PK) 和丙酮酸脱氢酶 E2 组分 (aceF) 基因分别显着增加了 12.9 倍和 13.9 倍，导致更多的丙酮酸和乙酰辅酶 A 生成，这有利于类胡萝卜素和脂肪酸的生物合成。甲基赤藓糖醇 4-磷酸 (MEP) 途径介导类胡萝卜素前体异戊烯基二磷酸 (IPP) 合成，因为所有八个相关基因都被上调。随着虾青素途径基因的增加，朝向虾青素生物合成的碳通量。碳的重新分配也促进了 TAG 的积累。此外，二酰基甘油酰基转移酶 (DGAT) 和磷脂的上调：二酰基甘油酰基转移酶 (PDAT) 基因表明酰基辅酶 A 依赖性和独立途径均调节 TAG 积累。因此，这项工作揭示了碳代谢响应氮饥饿的多重防御机制，扩展了我们对类胡萝卜素、TAG等重要代谢物合成的理解。因为所有八个相关基因都被上调。随着虾青素途径基因的增加，朝向虾青素生物合成的碳通量。碳的重新分配也促进了 TAG 的积累。此外，二酰基甘油酰基转移酶 (DGAT) 和磷脂的上调：二酰基甘油酰基转移酶 (PDAT) 基因表明酰基辅酶 A 依赖性和独立途径均调节 TAG 积累。因此，这项工作揭示了碳代谢响应氮饥饿的多重防御机制，扩展了我们对类胡萝卜素、TAG等重要代谢物合成的理解。因为所有八个相关基因都被上调。随着虾青素途径基因的增加，朝向虾青素生物合成的碳通量。碳的重新分配也促进了 TAG 的积累。此外，二酰基甘油酰基转移酶（DGAT）和磷脂的上调：二酰基甘油酰基转移酶（PDAT）基因表明酰基辅酶A依赖性和独立途径均调节TAG积累。因此，这项工作揭示了碳代谢响应氮饥饿的多重防御机制，扩展了我们对类胡萝卜素、TAG等重要代谢物合成的理解。二酰基甘油酰基转移酶（DGAT）和磷脂的上调：二酰基甘油酰基转移酶（PDAT）基因表明酰基辅酶A依赖性和独立途径均调节TAG积累。因此，这项工作揭示了碳代谢响应氮饥饿的多重防御机制，扩展了我们对类胡萝卜素、TAG等重要代谢物合成的理解。二酰基甘油酰基转移酶（DGAT）和磷脂的上调：二酰基甘油酰基转移酶（PDAT）基因表明酰基辅酶A依赖性和独立途径均调节TAG积累。因此，这项工作揭示了碳代谢响应氮饥饿的多重防御机制，扩展了我们对类胡萝卜素、TAG等重要代谢物合成的理解。