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Generation of Marked and Markerless Mutants in Model Cyanobacterial Species
Published on: May 29, 2016
Genome erosion in a nitrogen-fixing vertically transmitted endosymbiotic multicellular cyanobacterium
Liang Ran1, John Larsson, Theoden Vigil-Stenman
1Department of Botany, Stockholm University, Stockholm, Sweden.
Plos One
|July 15, 2010
Summary
The genome of a cyanobacterium in symbiosis with the Azolla water fern shows degradation, with many genes lost. This organism is evolving into a nitrogen-fixing plant entity, mimicking early chloroplast evolution.
Area of Science:
- Evolutionary Biology
- Genomics
- Symbiosis
Background:
- The origin of plant chloroplasts involved a cyanobacterial endosymbiosis.
- The precise mechanisms and partners in this event remain unclear.
Purpose of the Study:
- To investigate the genome of a unique extracellular cyanobacterial symbiont in the Azolla water fern.
- To understand the evolutionary trajectory of this symbiosis and its implications for early plant evolution.
Main Methods:
- Genome sequencing of the cyanobacterium from Azolla filiculoides.
- Analysis of gene content, pseudogenes, and transposable elements.
Main Results:
- The cyanobacterial genome is eroding, with 31.2% pseudogenes and numerous transposable elements.
- Essential genes for DNA replication and repair show pseudogenization.
- Genes for nitrogen fixation and cell differentiation are well-preserved, while core metabolic genes are lost.
Conclusions:
- This is the first observation of genome degradation in a plant-associated extracellular cyanobacterium.
- The Azolla cyanobiont is undergoing reductive genome evolution, transitioning towards a specialized nitrogen-fixing entity.
- This process may mirror the ancient transition of cyanobacteria to chloroplasts.
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