三角褐指藻单半乳糖基二酰基甘油MGDG合成酶及其代谢途径研究

Monogalactosyldiacylglycerol (MGDG) constitutes the most abundant polar lipids in thylakoid membrane and plays critical roles in thylakoid membrane assembly and function in diatoms. Nevertheless, the mechanisms of regulation in MGDG biosynthesis remain unknown in diatoms. In this study, we intend to use the model diatom Phaeodactylum tricornutum as a model system to investigate the role of MGDG synthase (Pt MGD), as the key enzyme in the biosynthesis of MGDG. A family of three putative Pt MGDs from P. tricornutum was predicted. EST database and quantitative proteomics analysis revealed the differential expression profiles of the three Pt MGDs under nitrogen deprivation, indicating their distinct functions in MGDG anabolism. In this study, we proposed to characterize the role of Pt MGDs by subcellular location analysis, enzymatic activity measurement as well as substrate selectivity determination, gene disruption by TALENs or suppression by RNAi. Combined with the expression profiles analysis of Pt MGD proteins under different stress conditions, this study will provide insights regarding the preliminary roles of Pt MGDs in MGDG anabolism in P. tricornutum.

单半乳糖基二酰基甘油(Monogalactosyldiacylglycerol, MGDG)是硅藻类囊体膜脂中含量最丰富的极性脂，对维持其类囊体膜的结构及功能发挥着重要的作用。然而，到目前为止，硅藻MGDG的合成路径及其调控机制尚未阐明。本项目拟以模式硅藻三角褐指藻(Phaeodactylum tricornutum)为材料研究MGDG合成的关键酶。三角褐指藻基因组中编码三个MGDG合成酶(Pt MGDs)。EST数据及定量蛋白质组分析显示不同胁迫条件下三个Pt MGDs的表达模式不同，表明它们在MGDG合成代谢中的功能可能存在差异。本项目拟采用亚细胞定位研究，酶活测定及底物特异性分析，TALEN敲除或RNAi敲降等技术手段，结合不同胁迫条件下表达模式分析，初步阐明Pt MGDs在三角褐指藻MGDG合成代谢中的功能。

硅藻单半乳糖基二酰基甘油(Monogalactosyldiacylglycerol, MGDG)对于维持其质体类囊体膜结构、光合作用及糖脂代谢等方面发挥着重要的作用。本项目以模式硅藻三角褐指藻(Phaeodactylum tricornutum)为材料研究MGDG合成的关键酶。首先我们研究了三角褐指藻3个MGDG合成酶(PtMGDs)不同胁迫条件下的表达模式，发现它们在缺磷时均上调表达，缺氮时均下调表达，而在高盐胁迫时响应不同，仅有PtMGD1上调表达，表明PtMGD1参与了硅藻应对高盐胁迫响应。亚细胞定位研究方面，3个PtMGDs均可以定位于质体，而高盐胁迫下PtMGD1少量细胞显示出胞质定位，可能与PtMGD1蛋白参与高盐逆境响应相关。遗传分析结果显示，PtMGD1基因敲除突变后，藻株生长速率、MGDG和DGDG含量、光合放氧速率等方面降低，同时TAG含量增加，PtMGD2及PtMGD3表型变化不明显，结合脂质组学分析结果，我们推测PtMGD1主要负责MGDG合成代谢中真核路径，同时参与硅藻高盐胁迫响应，本研究初步阐明PtMGDs在三角褐指藻MGDG合成代谢中的功能。