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Plastid Genome Sequence of the Cryptophyte Alga Rhodomonas salina CCMP1319: Lateral Transfer of Putative DNA Replication Machinery and
 

Summary: Plastid Genome Sequence of the Cryptophyte Alga Rhodomonas salina
CCMP1319: Lateral Transfer of Putative DNA Replication Machinery and
a Test of Chromist Plastid Phylogeny
Hameed Khan,* Natalie Parks,* Catherine Kozera, Bruce A. Curtis, Byron J. Parsons,
Sharen Bowman, and John M. Archibald*
*Genome Atlantic and the Canadian Institute for Advanced Research, Program in Evolutionary Biology, Department of Biochemistry
and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada; and The Atlantic Genome Centre, Halifax, Nova
Scotia, Canada
Cryptophytes are a group of unicellular algae with chlorophyll c­containing plastids derived from the uptake of
a secondary (i.e., eukaryotic) endosymbiont. Biochemical and molecular data indicate that cryptophyte plastids are
derived from red algae, yet the question of whether or not cryptophytes acquired their red algal plastids independent of
those in heterokont, haptophyte, and dinoflagellate algae is of long-standing debate. To better understand the origin and
evolution of the cryptophyte plastid, we have sequenced the plastid genome of Rhodomonas salina CCMP1319: at
135,854 bp, it is the largest secondary plastid genome characterized thus far. It also possesses interesting features not
seen in the distantly related cryptophyte Guillardia theta or in other red secondary plastids, including pseudogenes,
introns, and a bacterial-derived gene for the tau/gamma subunit of DNA polymerase III (dnaX), the first time putative
DNA replication machinery has been found encoded in any plastid genome. Phylogenetic analyses indicate that dnaX
was acquired by lateral gene transfer (LGT) in an ancestor of Rhodomonas, most likely from a firmicute bacterium.
A phylogenomic survey revealed no additional cases of LGT, beyond a noncyanobacterial type rpl36 gene similar to that
recently characterized in other cryptophytes and haptophytes. Rigorous concatenated analysis of 45 proteins encoded in

  

Source: Archibald, John - Department of Biochemistry and Molecular Biology, Dalhousie University

 

Collections: Biology and Medicine