Functional Genomics of Photosynthesis and Photoprotection in Chlamydomonas

green alga Chlamydomonas

 

The unicellular green alga Chlamydomonas reinhardtii is our model organism of choice for elucidating the detailed functions of genes involved in photosynthesis and photoprotection. Photosynthesis in Chlamydomonas is essentially identical to that in vascular plants, but unlike plants, Chlamydomonas can grow without photosynthesis, even in complete darkness. This ability allows for the isolation of mutants that are impaired in photosynthesis or in the mechanisms that protect the photosynthetic apparatus from photo-oxidative damage. Genetic tools available for Chlamydomonas include replica plating, tetrad analysis, and transformation of the nuclear and chloroplast genomes. An international Chlamydomonas genome project is identifying hundreds of new genes with potential roles in photosynthesis, and a challenge for the next decade is to determine the specific functions of these genes.

We are taking parallel forward and reverse genetics approaches to identify new genes that function in photosynthesis and photoprotection. Following insertional mutagenesis of the Chlamydomonas nuclear genome, we are using a battery of phenotypic screens to isolate a large collection of mutants that are impaired in photosynthesis, photoprotection, and responses to ROS. High-throughput cloning and sequencing of flanking genomic DNA from these mutants, coupled with classical genetic analysis, will enable us to establish a database of genes that are necessary for photosynthesis and photoprotection. Detailed biochemical and physiological characterization of the mutants will help to identify the specific functions and interactions of each gene.

We are also generating a collection of Chlamydomonas mutants resulting from chemical mutagenesis that can be screened for point mutations in any gene of interest. Recently developed mutation detection techniques allow the identification of nonsense and missense mutations in pools of DNA from the mutant collection. Phenotypic characterization of the mutants will allow us to determine the functions of many new Chlamydomonas genes.