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Research



Vision: The chloroplast fuels processes in plants, animals, and microbes directly or indirectly. We are interested in understanding how it provides carbon and energy at cellular and molecular levels and how its activity is regulated.

Question 1: How does the chloroplast export metabolites to the cytosol?

The carbon and energy captured by photosynthesis is stored in various metabolites that can be exported to the cytosol for further metabolism. We are particularly interested in the export mechanisms for lipid precursors, such as fatty acids and isopentenyl pyrophosphate (IPP), the building blocks for triacylglycerol (TAG) and terpenoids respectively.

Question 2: How does the chloroplast coordinate its activity with the nucleus?

Under nitrogen deprivation, plants and algae turn yellow, and accumulate TAG in lipid droplets. These might be responses to prevent energy excess: photosynthetic energy cannot be consumes by cellular growth. Decrease of the source—
energy capture by photosynthesis and increase of the sink—TAG help relieve this imbalance and associated detrimental effects. We suspect presence of energy excess signals to promote expression of lipid synthesis genes while repressing photosynthesis genes.

 

For questions 1 and 2, we will heavily employ the green algal model Chlamydomonas reinhardtii. Chlamydomonas combines the presence of a chloroplast with the advantages of a unicellular, haploid system. It facilitates understanding of chloroplast functions using high-throughput approaches.

Question 3: How does the chloroplast in marine photosynthetic eukaryotes function differently from that in land plants?

Heterokont algae, the most abundant algae in the oceans, have undergone a process known as secondary endosymbiosis. Consequently, they often harbor a chloroplast with four membranes, with the outermost one being part of their endomembrane system. How does this kind of chloroplast exchange metabolites and signals with other compartments of the cell? We will apply functional genomics, proteomics, and biochemical approaches in diatom model systems to answer these questions.