Intragenomic polymorphism and intergenomic recombination in the ribosomal RNA genes of strains belonging to a yeast species Pichia membranifaciens

ABSTRACT

A concerted evolution model has been proposed to explain the observed lack of sequence variation among the multiple ribosomal RNA (rRNA) gene copies in many different eukaryotic species. Recent studies on the level of intragenomic variations in the rRNA gene repeats of fungi resulted in controversial conclusions. In this study, we clearly showed that significant polymorphisms of the internal transcribed spacers (ITS1 and ITS2) of ribosomal DNA (rDNA) exist within the genome of a strain of the yeast species Pichia membranifaciens. More interestingly, we showed that the intragenomic ITS sequence polymorphisms were formed by intergenomic rDNA recombination among different P. membranifaciens strains with significantly different ITS sequences. Intergenomic rDNA recombination was also responsible for the diversification of rDNA sequences in different strains of the species. After the events bring together different rDNA types in individual genomes of the P. membranifaciens strains compared, rDNA sequence heterogeneity has remained in the genome of one but eliminated by homogenisation in the genomes of other strains. Our findings show new clue for further investigation on the mechanism of concerted evolution of rRNA genes in eukaryotes.

KEYWORDS:

• Ribosomal RNA gene
• intragenomic rDNA polymorphism
• intergenomic rDNA recombination
• concerted evolution
• Pichia membranifaciens

Acknowledgements

We thank Dr Vincent Robert from CBS, The Netherlands, for kindly supplying the yeast strains. We also thank Dr Alejandro P. Rooney, Agricultural Research Service, U.S. Department of Agriculture, USA, and Dr Jianping Xu, Department of Biology, McMaster University, Canada, for their invaluable suggestions and comments on this study and on the drafts of this manuscript. This study was supported by the National Natural Science Foundation of China (NSFC) under grant numbers 30470005 and 30825002.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by the National Natural Science Foundation of China (NSFC) under grant numbers 30470005 and 30825002.