Abstract
Previous work suggested that the tufA gene, encoding protein synthesis elongation factor Tu, was transferred from the chloroplast to the nucleus within the green algal lineage giving rise to land plants. In this report we investigate the timing and mode of transfer by examining chloroplast and nuclear DNA from the three major classes of green algae, with emphasis on the class Charophyceae, the proposed sister group to land plants. Filter hybridizations reveal a chloroplast tufA gene in all Ulvophyceae and Chlorophyceae and in some but not all Charophyceae. One charophycean alga, Coleochaete orbicularis, is shown to contain an intact but highly divergent chloroplast tufA gene, whose product is predicted to be non-functional in protein synthesis. We propose that a copy of the tufA gene was functionally transferred from the chloroplast to the nucleus early in the evolution of the Charophyceae, with chloroplast copies of varying function being retained in some but not all of the subsequently diverging lineages. This proposal is supported by the demonstration of multiple tufA-like sequences in Coleochaete nuclear DNA and in nuclear DNA from all other Charophyceae examined.
Highlights
A gene in all Ulvophyceae and Chlorophyceae and in some but not all Charophyceae
No tufA hybridization is seen to chloroplast DNA (cpDNA) from several basally derived branches of tracheophytes (Fig. 1), further supporting the notion that tufA is absent from all land plant cpDNAs [5, 8, 22]
The apparent presence of tufA in cpDNAs from three classes of green algae suggests that the gene was ancestrally present in green algal cpDNA [5]
Summary
A gene in all Ulvophyceae and Chlorophyceae and in some but not all Charophyceae. One charophycean alga, Coleochaete orbicularis, is shown to contain an intact but highly divergent chloroplast tufA gene, whose product is predicted to be nonfunctional in protein synthesis. We propose that a copy of the tufA gene was functionally transferred from the chloroplast to the nucleus early in the evolution of the Charophyceae, with chloroplast copies of varying function being retained in some but not all ofthe subsequently diverging lineages. The plant tufA gene encodes the chloroplast protein synthesis elongation factor Tu (EF-Tu). Phylogenetic analysis suggests that tufA was transferred from the chloroplast to the nucleus within the green algal lineage giving rise to land plants [5]. Five classes of green algae are recognized, with most taxa being assigned to the classes Charophyceae, Chlorophyceae, and Ulvophyceae [9]. To further characterize the transfer of the tufA gene, we have investigated its structure and subcellular location in members of these three classes of green algae. This article must be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact
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