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首页 » 中国科学院 » The Plant Cell:胡晗华等硅藻油脂积累机制研究获进展

The Plant Cell:胡晗华等硅藻油脂积累机制研究获进展

来源:水生生物研究所 2014-04-29 21:56

硅藻是藻类中的一个重要类群,作为主要的初级生产者,约占全球初级生产的五分之一,相当于整个热带雨林的净初级生产量。与多数藻类不同,硅藻同化产物主要是油或金藻多糖,其中油份以油滴状态贮存在细胞中,含量可占40~60%,因而被认为是最为合适的生物柴油原料之一。然而,目前其油脂积累的分子机制尚不清楚。

近日,中国科学院水生生物研究所副研究员胡晗华课题组以硅藻研究的模式种三角褐指藻为对象,揭示了硅藻油脂积累过程中不同代谢路径如何推动碳流流向甘油三酯的合成。他们首先通过差减杂交,发现一个与亮氨酸降解相关的基因MCC2在油脂积累过程中显著上调。通常认为油脂积累是伴随着营养盐的限制而发生的,因而在营养盐限制条件下,氨基酸降解是其必然的结果。但氨基酸降解的去向如何?是否均与油脂积累存在关系?这些问题并没有任何直接的证据。通过荧光定量PCR与非标记定量蛋白质组学手段(与水生所葛峰研究员合作完成)的分析显示在油脂积累过程中除氨基酸降解外,糖酵解、三羧酸循环、丙酮酸代谢、脂肪酸与甘油三酯合成等路径相关蛋白水平显著上调。显示油脂积累过程中,由氨基酸降解和细胞糖酵解产生的碳流进入到三羧酸循环,再经由苹果酸穿梭或直接以丙酮酸形式进入到叶绿体中用于脂肪酸的合成。功能验证结果显示,MCC2敲降藻株甘油三酯合成减少28~37%。有研究表明,在营养限制条件下三角褐指藻最多40%的脂是由细胞其他成分降解转化而来的。由此可见,可能仅仅是支链氨基酸尤其是亮氨酸的降解在三角褐指藻油脂积累过程中起主要作用。代谢物水平分析显示,MCC2敲降藻株中三种支链氨基酸的降解均受到不同程度的抑制。尽管谷氨酰胺、精氨酸、谷氨酸、脯氨酸、丙氨酸、鸟氨酸和天冬氨酸等的含量远高于三种支链氨基酸,然而,在油脂积累前,这些氨基酸含量均快速降至极低水平。实验进一步证明这些氨基酸由于直接或间接与硅藻特有的尿素循环相关,在细胞缺氮前即通过尿素循环分解形成氨和二氧化碳或合成多胺等物质贮存在胞内。实验也证明了缬氨酸的降解是通过首先形成亮氨酸来进行的。他们的实验首次阐明来自细胞糖酵解与支链氨基酸降解的碳流导致了硅藻细胞油脂的积累。

相关论文Methylcrotonyl-CoA carboxylase regulates triacylglycerol accumulation in the model diatom Phaeodactylum tricornutum 已于4月25日在线发表于Plant Cell。(生物谷Bioon.com)

生物谷推荐的英文摘要:

The Plant Cell    doi:10.?1105/?tpc.?114.?124982

Methylcrotonyl-CoA Carboxylase Regulates Triacylglycerol Accumulation in the Model Diatom Phaeodactylum tricornutum[C][W]

Feng Gea,1, Weichao Huangb,1, Zhuo Chenb,1, Chunye Zhangb,1, Qian Xionga, Chris Bowlerc, Juan Yangb, Jin Xub and Hanhua Hua,b,2

The model marine diatom Phaeodactylum tricornutum can accumulate high levels of triacylglycerols (TAGs) under nitrogen depletion and has attracted increasing attention as a potential system for biofuel production. However, the molecular mechanisms involved in TAG accumulation in diatoms are largely unknown. Here, we employed a label-free quantitative proteomics approach to estimate differences in protein abundance before and after TAG accumulation. We identified a total of 1193 proteins, 258 of which were significantly altered during TAG accumulation. Data analysis revealed major changes in proteins involved in branched-chain amino acid (BCAA) catabolic processes, glycolysis, and lipid metabolic processes. Subsequent quantitative RT-PCR and protein gel blot analysis confirmed that four genes associated with BCAA degradation were significantly upregulated at both the mRNA and protein levels during TAG accumulation. The most significantly upregulated gene, encoding the β-subunit of methylcrotonyl-CoA carboxylase (MCC2), was selected for further functional studies. Inhibition of MCC2 expression by RNA interference disturbed the flux of carbon (mainly in the form of leucine) toward BCAA degradation, resulting in decreased TAG accumulation. MCC2 inhibition also gave rise to incomplete utilization of nitrogen, thus lowering biomass during the stationary growth phase. These findings help elucidate the molecular and metabolic mechanisms leading to increased lipid production in diatoms.

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