When Simpler Is Better. Unicellular Green Algae for Discovering New Genes and Functions in Carbohydrate Metabolism

Of all algae, those in the division chlorophyta (green algae) display the closest relationship to the vascular plants. Chlorophytes harbor a chloroplast that is considered to have originated from a single endosymbiotic event and contain the same types of photosynthetic pigments as land plants. At variance with other divisions of algae, starch is produced within chlorophyte plastids and displays a structure very similar to that described for vascular plants. Considerable variation is found in the organization and composition of chlorophyte cell walls. Some are characterized by the presence of a simple glycoprotein wall, whereas others synthesize elaborate walls with a polysaccharide composition like that of land plants. Algae often contain pulsatile vacuoles that in some cases allow growth in the absence of a normal cell wall structure, a useful feature for studying wall biology. Because of the presence of plastids and plant-like cell walls, unicellular chlorophytes may be considered true plant-like eukaryotic microorganisms. Their microbial nature permits the use of extremely powerful genetic techniques akin to those in yeast (Saccharomyces cerevisiae) for the dissection of plant pathways. In this scientific correspondence, we will emphasize the potential of using unicellular chlorophytes to understand plant pathways, including polysaccharide and cell wall metabolism. We hope to encourage plant biologists to consider these species because of the potential for rapid progress in understanding many basic plant pathways.