New insights into the regulation of sexual reproduction in Closterium.

The genus Closterium, which is the closest unicellular relative to land plants, is the best-characterized charophycean green alga with respect to the process of sexual reproduction. In two representative heterothallic species, the steps and methods of intercellular communication were fully described. Glycoproteinaceous sex pheromones involved in the progress of these processes were physiologically and biochemically characterized and the corresponding genes were cloned. These pheromones function in most steps of sexual reproduction. For elucidating the mechanisms of sexual reproduction in detail, molecular tools such as expressed sequence tag, microarray analysis, and genetic transformation systems have been established, and whole genome analyses are ongoing. Finally, sexual reproductive isolation among mating groups was characterized, and the mechanism involved in this isolation was considered with respect to sex pheromones. In homothallic Closterium, the presence of a pheromone orthologous to the heterothallic type and possible sexual differentiation were also described, through the combination of closely related heterothallic cells.