Abstract
Dinoflagellates are a large group of algae that contribute significantly to marine productivity and are essential photosynthetic symbionts of corals. Although these algae have fully-functioning mitochondria and chloroplasts, both their organelle genomes have been highly reduced and the genes fragmented and rearranged, with many aberrant transcripts. However, nothing is known about their RNA polymerases. We cloned and sequenced the gene for the nuclear-encoded mitochondrial polymerase (RpoTm) of the dinoflagellate Heterocapsa triquetra and showed that the protein presequence targeted a GFP construct into yeast mitochondria. The gene belongs to a small gene family, which includes a variety of 3′-truncated copies that may have originated by retroposition. The catalytic C-terminal domain of the protein shares nine conserved sequence blocks with other single-subunit polymerases and is predicted to have the same fold as the human enzyme. However, the N-terminal (promoter binding/transcription initiation) domain is not well-conserved. In conjunction with the degenerate nature of the mitochondrial genome, this suggests a requirement for novel accessory factors to ensure the accurate production of functional mRNAs.
Highlights
Dinoflagellates are a large and diverse group of algae, which are major contributors to marine primary productivity and include the essential endosymbionts of corals [1,2]
We looked for organellar RNA polymerases in the photosynthetic dinoflagellate Heterocapsa triquetra and found a nuclear gene encoding a single subunit RNA polymerase of the RpoTm type
A Phage T7 type RNA Polymerase In higher plants and bryophytes, the mitochondrial bacteriophage-like RNA polymerase gene has been duplicated and its product retargeted to the chloroplast, where it is responsible for transcription of some housekeeping genes [18]
Summary
Dinoflagellates are a large and diverse group of algae, which are major contributors to marine primary productivity and include the essential endosymbionts of corals [1,2]. They include both photosynthetic and non-photosynthetic species, some of which have parasitic life-styles. The genomes of both the mitochondrion and the plastid are highly reduced and uniquely organized In both photosynthetic and non-photosynthetic dinoflagellates, the mitochondrial genomes carry genes for only three essential components of the electron transport chain (cob, cox and cox3) plus fragments of rRNA genes [4,5,6,7,8,9]. Both of the dinoflagellate organelle genomes have clearly been subjected to massive gene rearrangement in the course of reduction
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