Our lab studies the unicellular eukaryotic alga Chlamydomonas reinhardtii (Chlamydomonas website). Chlamydomonas has been used for decades as a model organism to study a wide range of research topics including organellar gene expression, the development and regulation of the photosynthetic electron transfer chain, flagellar assembly and cellular motility, and regulation of metabolic pathways. The organism is amenable to standard genetic analysis, a large collection of mutant strains is available, standard crosses can be done to define genetic loci and make different allelic combinations of genes, and genes can be cloned by complementation. The Chlamydomonas genome has been completely sequenced and annotated.
Chlamydomonas cells have a single chloroplast and can grow photosynthetically in a manner that is identical to that used by higher plants. They can also grow “heterotrophically” by metabolizing simple carbon sources such as acetate. Acetate is built into larger carbohydrates initially through the reactions of the glyoxylate cycle. This cycle partially overlaps with the Tricarboxylic Acid (TCA) cycle but its two key enzymes [isocitrate lyase (ICL) and malate synthase (MS)] bypass the two oxidative reactions of the TCA cycle that evolve carbon dioxide. The Chlamydomonas genome has multiple copies of genes encoding the enzymes of the glyoxylate cycle, highlighting the importance of this metabolic pathway to the cell.
RESEARCH QUESTIONS: Why does the Chlamydomonas genome have more than one copy of glyoxylate cycle genes? Do the encoded proteins work in different ways? Are they located differently in cells? Where does the glyoxylate cycle occur in Chlamydomonas cells?
We are also interested in how the glyoxylate cycle is used and regulated by Chlamydomonas cells. As an example, Chlamydomonas cells dramatically redirect their metabolism when deprived of nitrogen. Such cells accumulate oils in the form of triacylglycerols at high concentrations in their cytoplasm. Some researchers are using this as a potential and inexpensive source of biofuels. One of the ways that Chlamydomonas cells accomplish this metabolic shift is by down-regulating the expression of ICL and MS genes.
RESEARCH QUESTION: How are the genes encoding proteins involved in the glyoxylate cycle regulated in Chlamydomonas cells?
We have isolated a collection of Chlamydomonas mutants that are deficient in acetate uptake and/or assimilation. These mutants show interesting phenotypes that suggest unexpected features of glyoxylate cycle utilization and acetate metabolism.
RESEARCH QUESTION: What genes are impacted in these mutants?
We are currently using molecular biological, genomic, and bioinformatics approaches to identify these genes and determine the function of their gene products.
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