Metabolic modeling of carbon partitioning under the control of inositol polyphosphate signaling

光合藻类是地球碳循环的重要组成部分。二氧化碳被藻类吸收并转化为大分子，大分子是产生更多细胞的基础；或者，这种碳可以用来生产储存化合物，如淀粉和储存脂质（油）。我们对引导碳走向这些不同命运的代谢控制机制知之甚少。这个项目使用单细胞绿藻衣藻来研究在一个新发现的信号系统控制下的碳分配，这个信号系统涉及一种叫做肌醇多磷酸盐的特殊分子。光、碳和其他环境因素对肌醇多磷酸盐的调节将被确定，它们对碳代谢的影响将被测量和建模，从而确定它们控制细胞内碳分配的机制。这些研究将对光合代谢的关键方面提供更深入的了解，并使操纵藻类的策略得以发展，以提高生物技术相关化合物的产量。两名博士后研究员和多名本科生将在一个以执行变革科学和培养下一代科学家为使命的设施中接受藻类细胞生物学和生理学、代谢建模和质谱方面的跨学科培训和指导。生物学的一个主要挑战是了解细胞如何通过代谢网络控制碳的通量，以产生储存化合物，而不是生长以产生更多的细胞。该项目将破译一种新的细胞内信号传导模式，该模式使用肌醇多磷酸来控制模式光合真核生物衣藻的稳态代谢通量到中性脂。肌醇多磷酸及其生物合成酶在细胞内信号传导中发挥着多种作用，但以前没有将其与光合作用碳分配联系起来。由于肌醇多磷酸是保守的，本研究的结果可能广泛适用于了解藻类和植物的碳分配。PIs假设衣藻VIP1产生的肌醇多磷酸控制代谢反应，特别是影响储存脂质（三酰甘油）的产生。本研究将：1)对VIP1蛋白的体外活性进行表征，并测试其预测的催化活性是否为功能所必需；Ii)检验肌醇多磷酸异构体水平反映不同营养条件下生长代谢差异的假设；Iii)对野生型和vip1-1在不同营养条件下的转录组和代谢组进行表征，以确定突变体代谢调节发生改变的区域；iv)采用定量代谢通量模型（INST-MFA）确定受肌醇多磷酸盐影响的碳代谢分支点。这项研究将使主要来自少数族裔机构的本科生接触到尖端的科学仪器、分析方法和建模方法，并让博士后科学家参与到一个高度协作的项目中，该项目需要跨学科的整合，并为他们提供领导和指导的机会。

Photosynthetic algae are a critical component of the earth's carbon cycle. Carbon dioxide is taken up by algae and converted into macromolecules that are the building blocks for producing more cells; alternatively this carbon can be used to produce storage compounds such as starch and storage lipids (oil). Very little is known about the metabolic control mechanisms that direct carbon towards these different fates. This project uses the single celled green alga Chlamydomonas to investigate carbon partitioning under the control of a newly discovered signaling system involving a specialized class of molecules called inositol polyphosphates. The regulation of inositol polyphosphates by light, carbon and other environmental cues will be determined and their impact on carbon metabolism will be measured and modeled so that the mechanism by which they control intracellular carbon partitioning can be pinpointed. These studies will provide a deeper understanding of a key aspect of photosynthetic metabolism and enable the development of strategies for manipulating algae to improve yields of biotechnologically relevant compounds. Two postdoctoral fellows and multiple undergraduate will receive cross-disciplinary training and mentoring in algal cell biology and physiology, metabolic modeling and mass spectrometry in a facility whose mission is to perform transformative science and train the next generation of scientists. A major challenge in biology is understanding how cells control the flux of carbon through metabolic networks to produce storage compounds versus growth to produce more cells. This project will decipher a new mode of intracellular signaling that uses inositol polyphosphates to control steady state metabolic flux into neutral lipids in a model photosynthetic eukaryote, Chlamydomonas. Inositol polyphosphates and their biosynthetic enzymes play diverse roles in intracellular signaling, but have not been previously linked to photosynthetic carbon partitioning. Because inositol polyphosphates are conserved, the outcomes of this research are likely to be broadly applicable for understanding algal and plant carbon partitioning. The PIs hypothesize that inositol polyphosphates produced by Chlamydomonas VIP1 control metabolic responses that specifically impact the production of storage lipids (triacylglycerol). This research will: i) characterize VIP1 protein activity in vitro and test whether its predicted catalytic activities are required for function; ii) test the hypothesis that inositol polyphosphate isomer levels reflect differences in growth metabolism under different trophic conditions; iii) characterize transcriptomes and metabolomes of wild type and vip1-1 under different trophic conditions to identify areas where the mutant shows altered metabolic regulation; iv) employ quantitative metabolic flux modeling (INST-MFA) to identify branch points in carbon metabolism impacted by inositol polyphosphates. This research will expose undergraduates from a primarily minority institution to cutting edge scientific instrumentation, analytical methods and modeling approaches and engage post-doctoral scientists in a highly collaborative project that requires integration across diverse disciplines and provides them with leadership and mentoring opportunities.