Evolutionary mobility of the ribosomal DNA array in yeasts

Area of Science:

• Genomics
• Molecular Biology
• Eukaryotic Gene Organization

Background:

• Ribosomal DNA (rDNA) in eukaryotes forms large tandem arrays.
• Understanding the genomic organization and plasticity of rDNA is crucial for comprehending genome evolution.

Purpose of the Study:

• To compare the genomic locations of rDNA across yeast species.
• To investigate the evolutionary dynamics and potential mechanisms of rDNA array transposition within the Saccharomycetaceae family.

Main Methods:

• Comparative genomics analysis of rDNA locus positions in various yeast species.
• Identification of conserved and novel rDNA integration sites.
• Analysis of flanking genomic regions and associated genes.

Main Results:

• The large (>1 Mb) rDNA array has undergone multiple genomic transpositions within the Saccharomycetaceae family.
• An ancestral, non-telomeric rDNA site is conserved in species like Saccharomyces cerevisiae.
• In Lachancea, rDNA transposed to an internal chromosomal site near a tRNA gene; in other lineages, it moved to telomeric locations.
• Both ancestral and Lachancea rDNA sites are adjacent to genes (HMO1, CDC14) involved in maintaining rDNA chromatin structure.
• Loss of rDNA from the ancestral site typically resulted in complete disappearance without other regional rearrangements.

Conclusions:

• The rDNA array exhibits significant genomic mobility within yeast.
• RDNA transposition events appear to favor specific genomic contexts, often near genes regulating chromatin structure.
• The precise molecular mechanisms driving these large-scale rDNA movements remain to be elucidated but may involve DNA breaks or extrachromosomal elements.