Abstract Astaxanthin produced by Haematococcus pluvialis is an economically valuable ketocarotenoid pigment that benefits the health of human being. Astaxanthin can be accumulated in H. pluvialis cells up to 3% under high light stress. In this study, by adding 1 mM potassium iodide (KI) into the culture media of H. pluvialis cells under high light condition (HK), 26%–35% more astaxanthin than that of high light alone (HL) was obtained. As compared with HL that all cells turned into astaxanthin-rich non-motile ones at day 5 and day 10, about 30%–35% cells in HK remained flagella, which were motile without thickened secondary cell wall. Notably, these astaxanthin-rich motile cells contained more astaxanthin than astaxanthin-containing non-motile cells. The maximal photochemical efficiency (Fv/Fm) was higher in HK while the actual photochemical efficiency (Fv’/Fm') was lower in HK as compared with those in HL. Transcriptomes of cells in HK and HL groups were significantly different, especially at day 5 and day 10, which were consistent with above-mentioned morphological differences between HK and HL cells. KI promoted astaxanthin accumulation by up-regulating the transcription levels of astaxanthin biosynthetic genes and by simultaneously down-regulating the transcription levels of genes involved in other pathways that compete for precursors of astaxanthin biosynthesis. Transcriptomic data also revealed significant changes between HK and HL cells in genes involved in cell wall biosynthesis (57), flagella biosynthesis and cell movement (620), ROS homeostasis (42), and transcriptional factors (42). The possible mechanisms underlying KI's promoting role in H. pluvialis cells under high light were discussed based on morphological and transcriptomic data. In summary, this study provides a new method to increase astaxanthin accumulation in H. pluvialis, and its output expands current understanding of survival strategies and astaxanthin accumulation of H. pluvialis under high light stress.

中文翻译：

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比较转录组分析揭示了碘化钾对高光胁迫下雨生红球藻虾青素积累促进作用的机制

摘要 雨生红球藻产生的虾青素是一种具有经济价值的酮类胡萝卜素色素，有益于人类健康。在强光胁迫下，虾青素可在雨生红球藻细胞中累积高达 3%。在本研究中，通过在高光条件 (HK) 下将 1 mM 碘化钾 (KI) 加入雨生红球藻细胞的培养基中，获得比单独高光 (HL) 多 26%–35% 的虾青素。与HL在第5天和第10天所有细胞转变为富含虾青素的非运动细胞相比，HK中约30%-35%的细胞保留鞭毛，具有运动性且次生细胞壁不增厚。值得注意的是，这些富含虾青素的运动细胞比含有虾青素的非运动细胞含有更多的虾青素。与HL相比，HK的最大光化学效率(Fv/Fm)较高，而HK的实际光化学效率(Fv'/Fm')较低。HK和HL组细胞的转录组有显着差异，尤其是在第5天和第10天，这与上述HK和HL细胞之间的形态差异一致。KI 通过上调虾青素生物合成基因的转录水平并同时下调参与竞争虾青素生物合成前体的其他途径的基因的转录水平来促进虾青素的积累。转录组数据还揭示了 HK 和 HL 细胞在参与细胞壁生物合成 (57)、鞭毛生物合成和细胞运动 (620)、ROS 稳态 (42)、和转录因子 (42)。基于形态学和转录组学数据讨论了 KI 在高光下对雨生红球藻细胞的促进作用的可能机制。综上所述，本研究提供了一种增加雨生红球藻虾青素积累的新方法，其结果扩展了目前对雨生红球藻在强光胁迫下的生存策略和虾青素积累的理解。