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Comparative Chloroplast Genomics

Turmel, Monique [1], Otis, Christian [1], Lemieux, Claude [1].

The green algal ancestry of land plants as revealed by the chloroplast genome.

About 450 millions years ago, freshwater green algae belonging to the class Charophyceae emerged from their aquatic environment to colonize the land. This important event in the history of our planet ultimately gave rise to all the land plant species. Six monophyletic groups of charophycean green algae (Mesostigmatales, Chlorokybales, Klebsormidiales, Zygnematales, Coleochaetales, and Charales, given here in order of increasing cellular complexity) form together with the land plants the phylum Streptophyta. Recent analyses of the combined sequences of four genes from the nucleus (small subunit rRNA gene), chloroplast (atpB and rbcL) and mitochondria (nad5) of 25 charophycean green algae and eight green plants revealed that the Charales and land plants form a highly supported clade; however, moderate bootstrap support was observed for the positions of the other charophycean groups [Karol et al. (2001) Science 294:2351-2353]. The best tree in this four-gene analysis supports an evolutionary trend toward increasing cellular complexity. To gain deeper insight into the phylogeny of charophycean green algae and to understand how and when the highly conservative pattern displayed by land plant chloroplast DNAs originated in the Streptophyta, we have undertaken the sequencing of the chloroplast genome from representatives of all six charophycean lineages. To date, the complete chloroplast genome sequences of Mesostigma (Mesostigmatales), Chlorokybus (Chlorokybales), Staurastrum (Zygnematales), Zygnema (Zygnematales), Chaetosphaeridium (Coleochaetales), and Chara (Charales) have been determined. We have compared these genome sequences among themselves and with those available for three bryophytes. We will report the streptophyte phylogenies we have inferred from multiple chloroplast gene and protein sequences as well as our comparative analyses of chloroplast genome features (gene partitioning pattern, gene content, gene structure, gene order, and intron content).

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1 - Universite Laval, Biochimie et Microbiologie, Pavillon Charles-Eugene Marchand, Quebec, Québec, G1K 7P4, Canada

Charophycean green algae
Comparative genomics
Chloroplast genome
Streptophyte phylogeny.

Presentation Type: Symposium or Colloquium Presentation
Session: 19-1
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 2:00 PM
Abstract ID:83

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