Carpenter, Kevin, J. , Imanian, Behzad , Gangaeva, Anya, E. , Keeling, Patrick, J. .
Structural and functional integration of diatom tertiary endosymbionts of the dinoflagellates Kryptoperidinium foliaceum and Durinskia baltica.
Tertiary endosymbiosis, in which a eukaryote derives a plastid from a secondary alga (whose plastid was in turn derived from a primary alga), is found exclusively in dinoflagellates, where the evidence suggests at least three separate instances--once with a cryptophyte endosymbiont, once with a haptophyte, and once with a diatom. While the great majority of species derived from tertiary (and secondary) endosymbiosis contain a greatly reduced endosymbiont comprising only the plastid and perhaps an additional membrane or two, dinoflagellates with diatom tertiary endosymbionts are a very notable exception in their retention of nuclei as well as mitochondria. We examined two such diatom-containing dinoflagellate species--Kryptoperidinium foliaceum and Durinskia baltica--at the molecular and ultrastructural levels to better understand the functional and structural integration and reduction of the diatom endosymbiont with the dinoflagellate host. Phylogenetic analysis of genomic DNA and RNA (by RT-PCR), along with other molecular evidence, strongly supports the presence of actively expressed mitochondrial genes involved in electron transport (e.g., cox1, cob) from both endosymbiont as well as host mitochondria in both species. Likewise, ultrastructural examination reveals endosymbiont mitochondria of normal size with well-developed tubular cristae, structures usually lost at early stages of mitochondrial reduction. All of this evidence strongly suggests that K. foliaceum and D. baltica represent the first known instances of organisms with functional mitochondria of two distinct evolutionary origins. Examination of ultrastructure of K. foliaceum using TEM, similarly shows a lack of structural reduction in the endosymbiont, aside from the loss of its siliceous frustule and motility. The endosymbiont appears to occupy a volume at least as large (if not larger) than the host and lies peripheral to it, nearly surrounding it. However, the association of the two cells’ cytoplasms appears topologically complex--one issue we are attempting to elucidate with whole cell modeling.
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1 - University of British Columbia, Canadian Institute for Advanced Research, Botany Department, 3529-6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
2 - University of British Columbia, Canadian Institute for Advanced Research, Botany Depatment, 3529-6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 11:00 AM