Transcriptome comparisons for autotrophic and mixotrophic growth of Chlamydomonas
Martin H. Spalding1, Wei Fang1, Yingjun Wang1, Madeli Castruita2, David Casero3, Matteo Pellegrini3,4 and Sabeeha Merchant2,4
1) Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA
2) Department of Chemistry and Biochemistry, UCLA, Los Angeles, CA
3) Department of Molecular, Cell and Development Biology, UCLA, Los Angeles, CA
4) Institute for Genomics and Proteomics, Los Angeles, CA
Chlamydomonas reinhardtii can grow autotrophically, using only CO2, light and mineral nutrients, but also can use acetate as a fixed carbon source for either mixotrophic or heterotrophic growth. Both mixotrophic and heterotrophic growth have been used experimentally for decades, but relatively little is known about acetate metabolism under either condition or about the effect of acetate on expression of photosynthesis related genes. We have compared the transcriptome profiles of Chlamydomonas under autotrophic and mixotrophic conditions. Only a modest increase was observed in the transcript abundance of genes expected to be involved in acetate metabolism in mixotrophic relative to autotrophic cells. Also somewhat unexpected was the finding that the abundance of most mRNAs encoding photosynthetic components is slightly higher in mixotrophic cells. Since autotrophic cells were grown in limiting CO2 (air-levels), where the CO2-concentrating mechanism of Chlamydomonas is induced, we compared the RNA abundance of known limiting-CO2 inducible genes in the two conditions. The addition of acetate (mixotrophic growth) has been suggested to have the same effect as elevated CO2 in repressing expression of limiting-CO2 inducible genes. Our data indicate this is true, but for only a subset of the known limiting CO2 inducible genes. For this subset, which represents about 1/3 of the known inducible genes, RNA abundance was reduced at least 3-fold by the presence of acetate. For most of the remaining inducible genes, RNA abundance was not more than 2-fold changed in either direction for autotrophic cells vs. mixotrophic cells, although there are a few genes for which the RNAs are actually substantially increased in abundance in mixotrophic conditions.
e-mail address of presenting author: