Molecular Genetics and Genomics

, Volume 276, Issue 5, pp 464–477

Distinctive architecture of the chloroplast genome in the chlorophycean green alga Stigeoclonium helveticum

  • Anne-Sophie Bélanger
  • Jean-Simon Brouard
  • Patrick Charlebois
  • Christian Otis
  • Claude Lemieux
  • Monique Turmel
Original Paper

DOI: 10.1007/s00438-006-0156-2

Cite this article as:
Bélanger, A., Brouard, J., Charlebois, P. et al. Mol Genet Genomics (2006) 276: 464. doi:10.1007/s00438-006-0156-2

Abstract

The chloroplast genome has experienced many architectural changes during the evolution of chlorophyte green algae, with the class Chlorophyceae displaying the lowest degree of ancestral traits. We have previously shown that the completely sequenced chloroplast DNAs (cpDNAs) of Chamydomonas reinhardtii (Chlamydomonadales) and Scenedesmus obliquus (Sphaeropleales) are highly scrambled in gene order relative to one another. Here, we report the complete cpDNA sequence of Stigeoclonium helveticum (Chaetophorales), a member of a third chlorophycean lineage. This genome, which encodes 97 genes and contains 21 introns (including four putatively trans-spliced group II introns inserted at novel sites), is remarkably rich in derived features and extremely rearranged relative to its chlorophycean counterparts. At 223,902 bp, Stigeoclonium cpDNA is the largest chloroplast genome sequenced thus far, and in contrast to those of Chlamydomonas and Scenedesmus, features no large inverted repeat. Interestingly, the pattern of gene distribution between the DNA strands and the bias in base composition along each strand suggest that the Stigeoclonium genome replicates bidirectionally from a single origin. Unlike most known trans-spliced group II introns, those of Stigeoclonium exhibit breaks in domains I and II. By placing our comparative genome analyses in a phylogenetic framework, we inferred an evolutionary scenario of the mutational events that led to changes in genome architecture in the Chlorophyceae.

Keywords

ChlorophytaPlastid genome evolutionGene orderOrigin of replicationGroup II intronsRepeated sequences

Supplementary material

438_2006_156_MOESM1_ESM.pdf (4.1 mb)
Supplementary material

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Anne-Sophie Bélanger
    • 1
  • Jean-Simon Brouard
    • 1
  • Patrick Charlebois
    • 1
  • Christian Otis
    • 1
  • Claude Lemieux
    • 1
  • Monique Turmel
    • 1
  1. 1.Département de biochimie et de microbiologie, Pavillon Charles-Eugène MarchandUniversité LavalQuebec CityCanada