Subcellular localization of minicircle DNA in the dinoflagellate A mphidinium massartii

Summary Peridinin‐containing dinoflagellates have small circular DNA molecules called minicircle DNAs , each of which encodes one, or occasionally a few, plastid proteins or ribosomal RNA . Dinoflagellate minicircle DNA is composed of two parts: a gene‐coding sequence and a non‐coding sequence that consists of several variable and core regions. The core regions are identical among the minicircle DNAs with different genes within a species or strain. Because such structure is very different from those of well known plastid DNAs , many functional and evolutionary questions have been raised for the minicircle DNAs , and several studies that focus on answering those questions are underway. However, the localization of minicircle DNA is still controversial: several lines of indirect evidence have implied plastid localization, whereas the nuclear localization of minicircle DNA has also been suggested in a species. In order to understand the evolution and function of minicircle DNA , it is important to know its precise localization. In this study, we sequenced two typical minicircle DNAs , one encodes psbA and the other encodes 23S rRNA genes, from an A mphidinium massartii strain ( TM16 ). To determine the subcellular localization of these minicircle DNAs , we performed DNA ‐targeted whole cell fluorescence in situ hybridization with A . massartii minicircle DNA ‐specific probes and demonstrated that minicircle DNAs were present in plastids. This study provides the first direct evidence for the plastid localization of dinoflagellate minicircle DNAs .