Chloroplast division is regulated by the circadian expression ofFTSZandMINgenes inChlamydomonas reinhardtii

FTSZ and MIN proteins play important roles in plastid division. Having previously identified FTSZ genes in Chlamydomonas reinhardtii, we have now isolated the nucleus-encoded MIND and MINE1 genes from this species. Sequence analyses showed that MIND is highly conserved, while MINE1 is less well conserved. Both proteins were localized to chloroplasts, probably due to their N-terminal transit peptides. The transcription levels of FTSZ and MIN genes in synchronous cultures of C. reinhardtii, in which the chloroplasts divided synchronously with their host cells, were examined. Semi-quantitative reverse transcription PCR (RT-PCR) analyses showed that mRNA abundance displayed a circadian pattern under light-dark cycles and continuous light and dark conditions. Maximal mRNA levels correlated with cell division, and thus, chloroplast division. This work indicates that plastid division is regulated by the circadian expression of FTSZ and MIN genes.