THE USE OF CHLAMYDOMONAS (CHLOROPHYTA: VOLVOCALES) AS A MODEL ALGAL SYSTEM FOR GENOME STUDIES AND THE ELUCIDATION OF PHOTOSYNTHETIC PROCESSES

Abstract

Chlamydomonas reinhardtii Dangeard is a unicellular, haploid green alga that has been used as a model genetic system to investigate basic biological processes in photosynthetic eukaryotes. This organism has been particularly useful for dissecting photosynthesis because it can grow heterotrophically as well as photoautotrophically; this has allowed for the isolation and characterization of a large number of mutants that are completely devoid of photosynthetic CO2 fixation. Over the past 10 years there has been a dramatic increase in the number of molecular technologies that can be applied to studies of Chlamydomonas, enhancing its value as a model organism. Nuclear transformation has enabled researchers to generate and complement a range of different mutants and to investigate transcriptional control of gene expression in vivo. The development of methods for chloroplast transformation has helped elucidate the functions of chloroplast genes and the factors that modulate their expression. Genome‐wide studies will further enhance the value of Chlamydomonas as a resource for the biological community and will have a profound effect on the types of experimentation for which this alga is used. For example, the generation and characterization of a library of expressed sequence tags (ESTs) would identify cDNAs for most of the genes present on the Chlamydomonas genome. DNA microarray technology could be used to place these cDNAs on “chips,” configured from microscope slides, that would enable investigators to monitor changes in gene expression of essentially the entire genome simultaneously. The development of methods to identify strains harboring insertions in specific genes would help elucidate the functions of the genes that are represented in the EST library and that have been characterized for expression via the microarray technology. The production of linked physical and genetic maps would facilitate the map‐based cloning of any gene identified by a mutant phenotype. Finally, completing the sequence of the chloroplast genome and analyzing the function and expression of individual chloroplast genes would enhance our knowledge of the activities and biogenesis of this organelle. In thisreview we discuss the application of genomic technologies to studies of Chlamydomonas and how they would help elucidate the metabolism of plants, especially with respect to photosynthetic processes.