Actin Phylogeny Identifies Mesostigma viride as a Flagellate Ancestor of the Land Plants |
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Authors: | Debashish Bhattacharya Klaus Weber Seon Sook An Wolfgang Berning-Koch |
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Institution: | Department of Biological Sciences, University of Iowa, 239 Biology Building, Iowa City, IA 52242-1324, USA, US Department of Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 G?ttingen, Germany, DE
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Abstract: | Green algae and land plants trace their evolutionary history to a unique common ancestor. This ``green lineage' is phylogenetically
subdivided into two distinct assemblages, the Chlorophyta and the Streptophyta. The Chlorophyta includes the Chlorophyceae,
Trebouxiophyceae, Ulvophyceae, and Prasinopohyceae, whereas the Streptophyta includes the Charophyceae plus the bryophytes,
ferns, and all other multicellular land plants (Embryophyta). The Prasinophyceae is believed to contain the earliest divergences
within the green lineage. Phylogenetic analyses using rDNA sequences identify the prasinophytes as a paraphyletic taxon that
diverges at the base of the Chlorophyta. rDNA analyses, however, provide ambiguous results regarding the identity of the flagellate
ancestor of the Streptophyta. We have sequenced the actin-encoding cDNAs from Scherffelia dubia (Prasinophyceae), Coleochaete scutata, Spirogyra sp. (Charophyceae), and the single-copy actin gene from Mesostigma viride (Prasinophyceae). Phylogenetic analyses show Mesostigma to be the earliest divergence within the Streptophyta and provide direct evidence for a scaly, biflagellate, unicellular
ancestor for this lineage. This result is supported by the existence of two conserved actin-coding region introns (positions
20-3, 152-1), and one intron in the 5′-untranslated region of the actin gene shared by Mesostigma and the embryophytes.
Received: 10 July 1997 / Accepted: 9 April 1998 |
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Keywords: | : Actin — Chlorophyta — Green algae — Land plants — Mesostigma viride— Phylogeny — Prasinophyceae — Streptophyta |
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