Background Chromochloris zofingiensis is emerging as an industrially relevant alga given its robust growth for the production of lipids and astaxanthin, a value-added carotenoid with broad applications. Nevertheless, poor understanding of astaxanthin synthesis has limited engineering of this alga for rational improvements. Results To reveal the molecular mechanism underlying astaxanthin accumulation in C. zofingiensis, here we conducted an integrated analysis by combining the time-resolved transcriptomes and carotenoid profiling in response to nitrogen deprivation (ND). A global response was triggered for C. zofingiensis to cope with the ND stress. Albeit the little variation in total carotenoid content, individual carotenoids responded differentially to ND: the primary carotenoids particularly lutein and β-carotene decreased, while the secondary carotenoids increased considerably, with astaxanthin and canthaxanthin being the most increased ones. The carotenogenesis pathways were reconstructed: ND had little effect on the carbon flux to carotenoid precursors, but stimulated astaxanthin biosynthesis while repressing lutein biosynthesis, thereby diverting the carotenoid flux from primary carotenoids to secondary carotenoids particularly astaxanthin. Comparison between C. zofingiensis and Haematococcus pluvialis revealed the distinctive mechanism of astaxanthin synthesis in C. zofingiensis. Furthermore, potential bottlenecks in astaxanthin synthesis were identified and possible engineering strategies were proposed for the alga. Conclusions Collectively, these findings shed light on distinctive mechanism of carotenogenesis for astaxanthin biosynthesis in C. zofingiensis, identify key functional enzymes and regulators with engineering potential and will benefit rational manipulation of this alga for improving nutritional traits.

中文翻译：

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时间分辨类胡萝卜素分析和转录组学分析揭示了产油绿藻 Chromochloris zofingiensis 合成虾青素的胡萝卜素生成机制。

背景 Chromochloris zofingiensis 正在成为一种工业相关的藻类，因为它在生产脂质和虾青素方面的强劲增长，虾青素是一种具有广泛应用的增值类胡萝卜素。然而，对虾青素合成的了解不足限制了对这种藻类进行合理改进的工程设计。结果 为了揭示 C. zofingiensis 虾青素积累的分子机制，我们在此通过结合时间分辨转录组和类胡萝卜素分析对氮剥夺 (ND) 的反应进行了综合分析。C. zofingiensis 引发了全球响应以应对 ND 压力。尽管总类胡萝卜素含量变化不大，但个别类胡萝卜素对 ND 的反应不同：主要类胡萝卜素，尤其是叶黄素和 β-胡萝卜素减少，而次生类胡萝卜素明显增加，其中虾青素和角黄素增加最多。重建了类胡萝卜素生成途径：ND对类胡萝卜素前体的碳通量几乎没有影响，但在抑制叶黄素生物合成的同时刺激虾青素生物合成，从而将类胡萝卜素通量从初级类胡萝卜素转向次级类胡萝卜素，特别是虾青素。C. zofingiensis 和雨生红球藻之间的比较揭示了 C. zofingiensis 虾青素合成的独特机制。此外，还确定了虾青素合成中的潜在瓶颈，并为藻类提出了可能的工程策略。结论 总的来说，这些发现揭示了 C. zofingiensis 虾青素生物合成的胡萝卜素生成的独特机制，