Another new rising model among algal species is the primary red alga Cyani-dioschyzon merolae. C. merolae is another small unicellular organism (diameter 1.5 ^m). It lives in sulfate-rich hot springs (pH 1.5, 45 °C) (De Luca et al. 1978, as cited in Misumi et al. 2005). Similarly to O. tauri, C. merolae is wall-less and contains single mitochondrion, chloroplast, and nucleus. At 17 Mb, its nuclear genome is slightly bigger than that of O. tauri but still very small; a completed genomic sequence is available (Matsuzaki et al. 2004), and the chloroplast and mitochondrial genomes are also completed (Ohta et al. 1998, 2003).
C. merolae divides by binary fission with chloroplast dividing first, followed by mitochondrion and nucleus. The cell cycle can be synchronized by light/dark cycles to a degree similar to O. tauri cells (approx. 40% dividing cell at one time point). Synchrony can be increased by the use of aphidicolin which blocks nuclear and cellular division (but not chloroplast division) (Itoh et al. 1996). On the contrary, propyzamide and nocodazole have no effect on the cell cycle progression (Terui et al. 1995). Recently, a protocol for nuclear DNA transformation by homologous recombination has been reported (Minoda et al. 2004). It is the first case of a DNA transformation by homologous recombination of the nuclear genome being reported in a unicellular alga. This technique will undoubtedly speed up the reverse genetics of this model (Minoda et al. 2004).
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