ABSTRACTA critical relationship exists between reef-building corals and their photosynthetic endosymbionts. As important as this relationship is for reef health, it is exquisitely delicate—exposure to temperatures only marginally above the average summer maximum can cause corals to bleach, expelling their resident algae. Interestingly, several studies indicate that failure of corals to properly regulate symbiont cell divisions at high temperatures may cause bleaching. This needs to be further investigated, but first, it is necessary to decipher the molecular mechanisms controlingl the cell division cycle in these organisms. As a first step toward this goal, we identified key cell cycle-regulating genes in the recently published genome of the symbiotic dinoflagellate Symbiodinium minutum. We then correlated expression of these genes with cell cycle phase in diurnally growing S. minutum in culture. Of particular interest, this approach allowed us to identify cyclins and cyclin-dependent kinases that are involved in the G1/S transition—a likely point for coral cells to exert control over algal cell divisions.
Ultrastructural observation of a symbiotic dinoflagellate Zooxanthella nutricula from radiolarians collected off the northwestern coast of Okinawa Island, Japan
