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Preparation of Prokaryotic and Eukaryotic Organisms Using Chemical Drying for Morphological Analysis in Scanning Electron Microscopy (SEM)
Published on: January 7, 2019
Novel nucleomorph genome architecture in the cryptomonad genus hemiselmis
Christopher E Lane1, John M Archibald
1Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS B3H 1X5, Canada. c.lane@dal.ca
The Journal of Eukaryotic Microbiology
|November 25, 2006
Summary
Cryptomonad nucleomorph genomes typically have three chromosomes with ribosomal DNA repeats. This study found an exception in Hemiselmis rufescens, lacking these repeats on one chromosome, suggesting recombination shapes genome structure.
Area of Science:
- Eukaryotic genomics
- Algal endosymbiosis
- Molecular evolution
Background:
- Cryptomonads are unicellular eukaryotes with a photosynthetic red algal endosymbiont.
- The endosymbiont's genome is reduced to a nucleomorph, usually with three chromosomes.
- Nucleomorphs characteristically possess subtelomeric ribosomal DNA (rDNA) repeats.
Purpose of the Study:
- To investigate the nucleomorph genome architecture of the cryptomonad Hemiselmis rufescens.
- To identify exceptions to the canonical nucleomorph genome structure in cryptomonads.
- To understand the role of recombination in shaping nucleomorph genomes.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) to separate and size nucleomorph chromosomes.
- Southern hybridizations using nucleomorph protein gene probes.
- Comparative analysis of nucleomorph genome structure across cryptomonad species.
Main Results:
- The Hemiselmis rufescens nucleomorph genome is approximately 580 kb, slightly larger than Guillardia theta.
- Subtelomeric rDNA repeats are absent on both ends of the second largest chromosome in H. rufescens.
- This absence of rDNA repeats represents the first known exception to canonical nucleomorph genome architecture.
Conclusions:
- The nucleomorph genome architecture in cryptomonads is not universally conserved.
- Recombination plays a significant role in shaping the karyotype and genomic structure of cryptomonad nucleomorphs.
- The findings challenge the established model of nucleomorph genome organization.
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