Schizochytrium species are known for their abundant production of docosahexaenoic acid (DHA). Low temperatures can promote the biosynthesis of polyunsaturated fatty acids (PUFAs) in many species. This study investigates low-temperature effects on DHA biosynthesis in Schizochytrium sp. TIO01 and its underlying mechanism. The Schizochytrium fatty acid biosynthesis pathway was evaluated based on de novo genome assembly (contig N50 = 2.86 Mb) and iTRAQ-based protein identification. Our findings revealed that desaturases, involved in DHA synthesis via the fatty acid synthase (FAS) pathway, were completely absent. The polyketide synthase (PKS) pathway and the FAS pathway are, respectively, responsible for DHA and saturated fatty acid synthesis in Schizochytrium. Analysis of fatty acid composition profiles indicates that low temperature has a significant impact on the production of DHA in Schizochytrium, increasing the DHA content from 43 to 65% of total fatty acids. However, the expression levels of PKS pathway genes were not significantly regulated as the DHA content increased. Further, gene expression analysis showed that pathways related to the production of substrates (acetyl-CoA and NADPH) for fatty acid synthesis (the branched-chain amino acid degradation pathway and the pentose phosphate pathway) and genes related to saturated fatty acid biosynthesis (the FAS pathway genes and malic enzyme) were, respectively, upregulated and downregulated. These results indicate that low temperatures increase the DHA content by likely promoting the entry of relatively large amounts of substrates into the PKS pathway. In this study, we provide genomic, proteomic, and transcriptomic evidence for the fatty acid synthesis pathway in Schizochytrium and propose a mechanism by which low temperatures promote the accumulation of DHA in Schizochytrium. The high-quality and nearly complete genome sequence of Schizochytrium provides a valuable reference for investigating the regulation of polyunsaturated fatty acid biosynthesis and the evolutionary characteristics of Thraustochytriidae species.

中文翻译：

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低温对裂殖壶菌二十二碳六烯酸生物合成的影响。 TIO01及其提出的底层机制


裂殖壶菌属物种以其丰富的二十二碳六烯酸 (DHA) 产量而闻名。低温可以促进许多物种多不饱和脂肪酸（PUFA）的生物合成。本研究探讨低温对裂殖壶菌 DHA 生物合成的影响。 TIO01及其底层机制。基于从头基因组组装（重叠群 N50 = 2.86 Mb）和基于 iTRAQ 的蛋白质鉴定来评估裂殖壶菌脂肪酸生物合成途径。我们的研究结果表明，通过脂肪酸合酶 (FAS) 途径参与 DHA 合成的去饱和酶完全不存在。聚酮合酶 (PKS) 途径和 FAS 途径分别负责裂殖壶菌中 DHA 和饱和脂肪酸的合成。脂肪酸组成谱分析表明，低温对裂殖壶菌 DHA 的产生有显着影响，使 DHA 含量从总脂肪酸的 43% 增加到 65%。然而，随着DHA含量的增加，PKS途径基因的表达水平并未受到显着调节。此外，基因表达分析表明，与脂肪酸合成底物（乙酰辅酶A和NADPH）产生相关的途径（支链氨基酸降解途径和磷酸戊糖途径）以及与饱和脂肪酸生物合成相关的基因（ FAS途径基因和苹果酸酶分别上调和下调。这些结果表明，低温可能通过促进相对大量的底物进入 PKS 途径来增加 DHA 含量。 在本研究中，我们为裂殖壶菌中的脂肪酸合成途径提供了基因组学、蛋白质组学和转录组学证据，并提出了低温促进裂殖壶菌中 DHA 积累的机制。高质量且近乎完整的裂殖壶菌基因组序列为研究多不饱和脂肪酸生物合成调控和破囊壶菌科物种的进化特征提供了有价值的参考。