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

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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.