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Nucleomorph Ribosomal DNA and Telomere Dynamics in Chlorarachniophyte Algae
Author(s) -
SILVER TIA D.,
MOORE CHRISTA E.,
ARCHIBALD JOHN M.
Publication year - 2010
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.2010.00511.x
Subject(s) - biology , genetics , genome , ribosomal dna , ribosomal rna , genome size , evolutionary biology , gene , phylogenetics
. Chlorarachniophytes are enigmatic marine unicellular algae that acquired photosynthesis by secondary endosymbiosis. Chlorarachniophytes are unusual in that the nucleus of the engulfed algal cell (a green alga) persists in a miniaturized form, termed a nucleomorph. The nucleomorph genome of the model chlorarachniophyte, Bigelowiella natans CCMP621, is 373 kilobase pairs (kbp) in size, the smallest nuclear genome characterized to date. The B. natans nucleomorph genome is composed of three chromosomes, each with canonical eukaryotic telomeres and sub‐telomeric ribosomal DNA (rDNA) operons transcribed away from the chromosome end. Here we present the complete rDNA operon and telomeric region from the nucleomorph genome of Lotharella oceanica CCMP622, a newly characterized chlorarachniophyte strain with a genome ∼610 kbp in size, significantly larger than all other known chlorarachniophytes. We show that the L. oceanica rDNA operon is in the opposite chromosomal orientation to that of B. natans . Furthermore, we determined the rDNA operon orientation of five additional chlorarachniophyte strains, the majority of which possess the same arrangement as L. oceanica , with the exception of Chlorarachnion reptans and those very closely related to B. natans . It is thus possible that the ancestral rDNA operon orientation of the chlorarachniophyte nucleomorph genome might have been the same as in the independently evolved, red algal‐derived, nucleomorph genomes of cryptophytes. A U2 small nuclear RNA gene was found adjacent to the telomere in Gymnochlora stellata CCMP2057 and Chlorarachnion sp. CCMP2014. This feature may represent a useful evolutionary character for inferring the relationships among extant lineages.