TYPE IV CHROMATIC ADAPTATION IN SYNECHOCOCCUS SP. RS9916
The picocyanobacterium Synechococcus is one of the largest genera of unicellular organisms performing photosynthesis. Synechococcus sp. RS9916 is a marine cyanobacteria isolated from the Red Sea. In changing light conditions, this organism undergoes a process called Type IV chromatic acclimation (CA4), which involves varying the accumulation of the light harvesting chromophores phycoerythrobilin and phycouroubilin within its light harvesting system under different wavelengths of light. Phycoerythrobilin, which absorbs green light, accumulates during growth in green light, while the blue-absorbing phycouroubilin accumulates in blue light. This organism is poorly studied, despite having a huge potential for affecting the earth’s atmosphere in terms of oxygen production. This organism has a small genome size (2.6 mega base pairs) that has been completely sequenced.
The Kehoe group is working with the group of Frédéric Partensky in Roscoff, France at CNRS to better understand the molecular physiology and regulation of CA4 in Synechococcus sp. RS9916. Toward this end, we are developing a genetic system for this organism, which will allow us to perform allelic replacement via homologous recombination. Our initial results suggest that homologous recombination is possible in this organism. One of our recent advances is our ability grow the cells on plates.
We are also studying molecular events occurring during CA4 using a functional genomics approach. We are performing genome wide tiling microarray experiments on this organism. We have compared the differences in the transcriptomes of cells grown in green light versus blue light in order to uncover the differential expression of genes during CA4 and identified the genes that are regulated by CA4. Our goal is to elucidate the signal transduction pathways that are responsible for triggering this phenotypic change. Our future efforts using this microarray data will also be to improve the gene annotations, since primary analysis of data also shows that some transcriptionally active regions exist that are not yet annotated. We are also performing a kinetic analysis of CA4 response with qRT-PCR, using cells that have been transferred from blue light to green light and vice versa. This experiment will identify genes that are rapidly upregulated after light shifts. The expression of these genes will be used to generate an action spectrum specific for CA4.