Molecular evolution of 5S ribosomal RNA from red and brown algae.

The cytoplasmic 5S ribosomal RNA (rRNA) sequences from seven red algae, a golden-yellow alga, a diatom and five brown algae have been determined. Using these sequences, phylogenic tree of these organisms have been constructed.Three types of algae, i.e., Rhodophyta (red algae), green algae (members of green plants), and Chromophyta (brown algae, the diatom and the goldenyellow alga) are only remotely related to one another phylogenically as deduced from the 5S rRNA sequences. Red algae emerged first in the eukaryotec evolution (1.3 to 1.4 billion years ago), and thereafter various fungi, green plants including green algae and Chromophyta emerged in this order. In the red algal evolution, the so-called "primitive group" of the class Bangiophyceae and "more advanced group" of the class Florideophyceae separated first from each other in an early stage of their evolution. The tree also indicates that various red algae, such as Batrachospermum, Gelidium, Gloiopeltis and Carpopeltis are phylogenically rather remote from one another. Thus, red algae are very widely and anciently separated organisms in the evolution of eukaryotes.Chromophyta contains golden-yellow algae, diatoms and brown algae. These three groups are related to one another. During the Chromophyta evolution, the golden-yellow alga separated first, and thereafter the diatom and brown algae separated from each other. Although brown algae are very different in their morphology and life cycle, the 5S rRNA sequences clearly indicate that the brown algae were diversified quite recently within a short period.