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Evolution and function of B chromosome 45S rDNA sequences in Brachycome dichromosomatica
Sylvia Marschner1, Armin Meister, Frank R Blattner
1Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany.
Genome
|September 26, 2007
Summary
The origin of Brachycome dichromosomatica B chromosomes is suggested to be from A chromosomes, predating cytodeme divergence. Micro B chromosome 45S rDNA is likely inactive, indicated by frequent nucleolar non-association.
Area of Science:
- Plant genetics
- Molecular evolution
- Cytogenetics
Background:
- Micro B chromosomes in Brachycome dichromosomatica harbor 45S ribosomal DNA (rDNA).
- Understanding the origin and activity of these B chromosome rDNA loci is crucial for evolutionary insights.
Purpose of the Study:
- To investigate the origin of 45S rDNA on micro B chromosomes.
- To assess the activity of 45S rDNA on micro B chromosomes.
Main Methods:
- Sequencing of the internal transcribed spacer 2 (ITS2) region of the 45S rRNA gene from A, large B, and micro B chromosomes.
- Phylogenetic analysis of ITS2 sequences.
- Analysis of nucleolar association patterns.
Main Results:
- Conserved sequence differences were found between A and B chromosome ITS2 sequences.
- Phylogenetic analysis did not support an external origin for B chromosome ITS2 sequences.
- Frequent nucleolar non-association (70%) was observed for micro B chromosomes.
Conclusions:
- The B chromosomes likely originated from A chromosomes before the divergence of Brachycome dichromosomatica cytodemes.
- The 45S rDNA on micro B chromosomes appears to be inactive, as evidenced by their lack of nucleolar association.
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