Chloroplast division and differentially regulated expression of ftsz1 and ftsz2 in the synchronous culture of nannochloris bacillaris (chlorophyta, trebouxiophyceae)

In plants, the prokaryote-derived chloroplast division protein FtsZ is divided into the FtsZ1 and FtsZ2 families. To clarify the relationship between FtsZ1 and FtsZ2 expression and chloroplast division in the unicellular green alga Nannochloris bacillaris, we compared FtsZ1 and FtsZ2 expression in alga cultured in 2 nutritionally different media. Cells grown in a rich medium had 1 FtsZ ring throughout the cell division cycle, whereas cells in an inorganic medium showed only 1 FtsZ ring during the chloroplast division phase. Both FtsZ1 and FtsZ1 mRNA levels in the rich medium were higher than those in the inorganic medium. However, a much larger difference in the amount of transcripts between cells cultured in the rich and in the inorganic media was observed in FtsZ1 than that in FtsZ1, suggesting different gene regulatory mechanisms between the FtsZ genes. N. bacillaris cells cultured in inorganic medium showed cell division photoperiodicity, whereas cells cultured in organic media proliferated continuously under a light/dark cycle. Although FtsZ1 was expressed constantly throughout the chloroplast division cycle in the rich medium, the increase in FtsZ1 mRNA level was simultaneous with chloroplast division under a light/dark cycle in the inorganic medium. FtsZ2 was expressed constantly in both media. The control of chloroplast division by regulating FtsZ ring formation is discussed.