Understanding Photosynthetic Electron Transport Using Chlamydomonas: The Path from Classical Genetics to High Throughput Genomics

Abstract

The Volvocales, an order of the green algal class Chlorophyceae, and the Streptophyte algae, the lineage that evolved into land plants, shared a common ancestor about one billion years ago. Chlamydomonas reinhardtii (Chlamydomonas throughout) a unicellular member of the Volvocales, has traditionally been considered a strong model organism that has been probed with sophisticated tools and methodologies to elucidate numerous biological processes. Perhaps the most in-depth analyses of Chlamydomonas have focused on defining proteins and complexes involved in the function and biogenesis of chloroplasts as well as the structure, assembly, and function of eukaryotic flagella (cilia); the latter are inherited from the common ancestor of animals and plants, but were lost during the evolution of land plants. This review emphasizes how Chlamydomonas has been used to elucidate a number of different activities associated with photosynthetic function. Many of these analyses were performed using classical genetic, biochemical and physiological approaches. However, recently, the DOE – Joint Genome Institute has sequenced the nuclear genome of Chlamydomonas (∼120 Mb) and has helped the community of researchers perform comparative genomic analyses. Comparisons of deduced Chlamydomonas proteins has identified a set of proteins specifically present in the green lineage and photosynthetic organisms, but not present in nonphotosynthetic organisms; this protein assemblage has been designated the GreenCut. Many proteins in the GreenCut are likely resident in the chloroplast and potentially associated with photosynthetic processes. Toward the end of this text we discuss the ways in which genomics has added a new dimension to our analyses of photosynthetic processes.