Transposition of a bacterial insertion sequence in chloroplasts
1Max-Planck-Institut für Molekulare Pflanzenphysiologie (MPI-MP), Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany.
The Plant Journal : for Cell and Molecular Biology
|January 16, 2009
Summary
Bacterial insertion sequences (IS elements) can transpose within plant chloroplasts, accumulating transposition intermediates. This study reveals plastids
Area of Science:
- Plant Molecular Biology
- Genetics and Genomics
- Bacterial Transposable Elements
Background:
- Bacterial transposable elements (IS elements) significantly influence genome structure, dynamics, and evolution.
- Understanding the mobility and behavior of these elements in different cellular compartments is crucial for genome stability research.
Purpose of the Study:
- To investigate the transposition capability of bacterial insertion sequences (IS elements), specifically Escherichia coli IS150, within the plant plastid (chloroplast).
- To explore the sequence dependency of IS150 integration and transposition initiation in the chloroplast genome.
- To assess the DNA repair mechanisms present in plastids, particularly non-homologous end joining (NHEJ).
Main Methods:
- Plastid transformation was employed to introduce various versions of the Escherichia coli IS150 element into the plastid genome of tobacco (Nicotiana tabacum) plants.
- Analysis of transposition intermediates and insertion sites within the chloroplast genome.
- Investigation of programmed ribosomal frame shifting for transposase synthesis in chloroplasts.
Main Results:
- The IS150 element was shown to be actively mobilized within the chloroplast, leading to the accumulation of numerous transposition intermediates.
- Programmed ribosomal frame shifting, essential for IS150 transposase synthesis, was confirmed to occur in chloroplasts.
- All detected IS150 insertion events targeted a single specific site in the plastid genome, indicating high sequence-dependent integration.
- Transposition initiation was independent of the surrounding DNA sequence.
- Plastids were found to lack the non-homologous end joining (NHEJ) DNA repair pathway.
Conclusions:
- Bacterial IS elements can transpose within the plant plastid, demonstrating functional mobility in this organelle.
- The high sequence specificity of IS150 integration suggests a unique mechanism for target site selection in chloroplasts.
- The absence of NHEJ in plastids has significant implications for genome stability and may explain their resistance to foreign DNA.
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