Abstract
In plant cells, plastid and mitochondrial DNA replication (organelle DNA replication, ODR) occurs ahead of the subsequent cell cycle composed of nuclear DNA replication (NDR) followed by cell division. Using the unicellular red alga Cyanidioschyzon merolae, we have shown this mechanism is also working as in higher plants. To examine the timing of ODR and NDR. We used quantitative PCR analysis (qPCR) with primers targeted to specific regions of each genome to monitor changes in the copy ratio of organelle DNA to nuclear DNA. We identified that ODR and NDR are coupled as occurring ODR prior to NDR. In synchronized cultures of C. merolae, specific inhibition of cyclin-dependent kinase (CDK) prevented NDR but not ODR after onset of the cell cycle. In contrast, inhibition of ODR by nalidixic acid also resulted in inhibition of NDR, indicating a strict dependence of NDR on ODR.
