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Controversy on chloroplast origins.
P J Lockhart1, D Penny, M D Hendy
1Molecular Genetics Unit, Massey University, Palmerston North, New Zealand.
FEBS Letters
|April 20, 1992
Summary
Conflicting data on photosynthetic organelle origins may stem from differing DNA GC content. This study suggests multiple origins for organelles, reconciling evolutionary tree inconsistencies.
Area of Science:
- Evolutionary Biology
- Molecular Biology
- Genetics
Background:
- Phylogenetic analyses of photosynthetic organelle origins yield contradictory evolutionary trees.
- Discrepancies arise from sequence, biochemical, and ultrastructural data sets.
- Existing methods may group sequences based on GC content rather than evolutionary relatedness.
Purpose of the Study:
- To propose a testable hypothesis explaining inconsistencies in organelle origin studies.
- To investigate the role of differing GC content in phylogenetic tree reconstruction.
- To reconcile conflicting data regarding the origins of photosynthetic organelles.
Main Methods:
- Analysis of sequence data with varying GC content.
- Comparison of phylogenetic trees generated from nuclear-encoded (high GC) and chloroplast-encoded (low GC) sequences.
- Evaluation of tree reconstruction methods' susceptibility to GC content bias.
Main Results:
- Phylogenetic methods group sequences with similar GC content, irrespective of evolutionary origin.
- Nuclear and chloroplast encoded sequences produce distinct phylogenetic trees due to GC content differences.
- Current data supports a hypothesis of multiple origins for photosynthetic organelles.
Conclusions:
- Differing GC content in DNA sequences is a significant factor causing inconsistencies in organelle evolutionary studies.
- Reconciliation of data suggests multiple independent origins for photosynthetic organelles.
- Evidence supports single origins for each type of light-harvesting complex.