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Phycological Section

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

The chloroplast genome sequence of the charophycean green alga Chara vulgaris: a structural analysis.

Six monophyletic groups of charophycean green algae form together with the land plants the phylum Streptophyta. Phylogenetic trees inferred from four genes residing in three cellular compartments revealed that the Charales form a highly supported clade with land plants and that the Coleochaetales diverged just before this clade [Karol et al. (2001) Science 294:2351-2353]. To investigate how the chloroplast genome evolved during the transition from charophycean green algae to land plants, we have undertaken the sequencing of chloroplast DNA (cpDNA) from representatives of the Charales (Chara vulgaris) and Coleochaetales (Chaetosphaeridium globosum). In the present study, we have compared the cpDNA sequence of Chara with those of Chaetosphaeridium and the bryophyte Marchantia polymorpha. Like the latter two cpDNAs, Chara cpDNA features a quadripartite structure with two copies of a rRNA-containing inverted repeat separating a large and a small single-copy region. However, at 184,933 bp, Chara cpDNA is substantially larger than Chaetosphaeridium (131,183 bp) and Marchantia (121,024 bp) cpDNAs. Given that all three genomes share a very similar gene repertoire, the lowest density of coding sequences (60.9%) is harbored by Chara cpDNA. By inferring the number of inversions required for converting the gene order of one genome into another, we find that Chara cpDNA is rearranged more extensively than its Chaetosphaeridium homolog relative to Marchantia cpDNA. Two group I introns and 16 group II introns reside in Chara cpDNA. Fifteen of these introns share homologs at identical positions in Chaetosphaeridium and land plant cpDNAs, one is missing in Chaetosphaeridium cpDNA, and two have not been identified in any streptophyte cpDNAs. Overall, our results support the idea that most of the typical features displayed by land plant cpDNAs (quadripartite structure, gene content, gene organization, and intron composition) were inherited from the common ancestor of the Coleochaetales and Charales.

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

Charophycean green algae
Chara vulgaris
Chloroplast genome
Comparative genomics.

Presentation Type: Poster
Session: 33-68
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:87

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