Chloroplast division checkpoint in eukaryotic algae.
Chloroplasts evolved from a cyanobacterial endosymbiont. It is believed that the synchronization of endosymbiotic and host cell division, as is commonly seen in existing algae, was a critical step in establishing the permanent organelle. Algal cells typically contain one or only a small number of chloroplasts that divide once per host cell cycle. This division is based partly on the S-phase-specific expression of nucleus-encoded proteins that constitute the chloroplast-division machinery. In this study, using the red alga Cyanidioschyzon merolae, we show that cell-cycle progression is arrested at the prophase when chloroplast division is blocked before the formation of the chloroplast-division machinery by the overexpression of Filamenting temperature-sensitive (Fts) Z2-1 (Fts72-1), but the cell cycle progresses when chloroplast division is blocked during division-site constriction by the overexpression of either FtsZ2-1 or a dominant-negative form of dynamin-related protein 5B (DRP5B). In the cells arrested in the prophase, the increase in the cyclin B level and the migration of cyclin-dependent kinase B (CDKB) were blocked. These results suggest that chloroplast division restricts host cell-cycle progression so that the cell cycle progresses to the metaphase only when chloroplast division has commenced. Thus, chloroplast division and host cell-cycle progression are synchronized by an interactive restriction that takes place between the nucleus and the chloroplast. In addition, we observed a similar pattern of cell-cycle arrest upon the blockage of chloroplast division in the glaucophyte alga Cyanophora paradoxa, raising the possibility that the chloroplast division checkpoint contributed to the establishment of the permanent organelle.
Department of Cell Genetics, National Institute of Genetics, Shizuoka 411-8540, Japan.|Core Research for Evolutional Science and Technology Program, Japan Science and Technology Agency, Saitama 332-0012, Japan.
Nobuko
N
Sumiya
Department of Cell Genetics, National Institute of Genetics, Shizuoka 411-8540, Japan.|Department of Genetics, Graduate University for Advanced Studies, Shizuoka 411-8540, Japan.
Takayuki
T
Fujiwara
Department of Cell Genetics, National Institute of Genetics, Shizuoka 411-8540, Japan.|Core Research for Evolutional Science and Technology Program, Japan Science and Technology Agency, Saitama 332-0012, Japan.
Atsuko
A
Era
Department of Cell Genetics, National Institute of Genetics, Shizuoka 411-8540, Japan; smiyagis@nig.ac.jp.|Core Research for Evolutional Science and Technology Program, Japan Science and Technology Agency, Saitama 332-0012, Japan.|Department of Genetics, Graduate University for Advanced Studies, Shizuoka 411-8540, Japan.
Shin-Ya
SY
Miyagishima
D002453:Cell Cycle; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002736:Chloroplasts / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D000461:Rhodophyta / Q000502:physiology*; D015854:Up-Regulation
D010940:Plant Proteins
Cyanidioschyzon merolae; Cyanophora paradoxa; algal cell cycle; chloroplast division