Journal Article

Genomic Origin and Organization of the Allopolyploid <i>Primula egaliksensis</i> Investigated by <i>in situ</i> Hybridization

Alessia Guggisberg, Célia Baroux, Ueli Grossniklaus and Elena Conti

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 7, pages 919-927
Published in print May 2008 | ISSN: 0305-7364
Published online February 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn026
Genomic Origin and Organization of the Allopolyploid Primula egaliksensis Investigated by in situ Hybridization

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Earlier studies have suggested that the tetraploid Primula egaliksensis (2n = 40) originated from hybridization between the diploids P. mistassinica (2n = 18) and P. nutans (2n = 22), which were hypothesized to be the maternal and paternal parent, respectively. The present paper is aimed at verifying the hybrid nature of P. egaliksensis using cytogenetic tools, and to investigate the extent to which the parental genomes have undergone genomic reorganization.

Methods

Genomic in situ hybridization (GISH) and fluorescent in situ hybridization (FISH) with ribosomal DNA (rDNA) probes, together with sequencing of the internal transcribed spacer (ITS) region of the rDNA, were used to identify the origin of P. egaliksensis and to explore its genomic organization, particularly at rDNA loci.

Key Results

GISH showed that P. egaliksensis inherited all chromosomes from P. mistassinica and P. nutans and did not reveal major intergenomic rearrangements between the parental genomes (e.g. interchromosomal translocations). However, karyological comparisons and FISH experiments suggested small-scale rearrangements, particularly at rDNA sites. Primula egaliksensis lacked the ITS-bearing heterochromatic knobs characteristic of the maternal parent P. mistassinica and maintained only the rDNA loci of P. nutans. These results corroborated sequence data indicating that most ITS sequences of P. egaliksensis were of the paternal repeat type.

Conclusions

The lack of major rearrangements may be a consequence of the considerable genetic divergence between the putative parents, while the rapid elimination of the ITS repeats from the maternal progenitor may be explained by the subterminal location of ITS loci or a potential role of nucleolar dominance in chromosome stabilization. These small-scale rearrangements may be indicative of genome diploidization, but further investigations are needed to confirm this assumption.

Keywords: Diploidization; FISH; genome evolution; GISH; hybridization; ITS; polyploidy; Primula egaliksensis; 45S rDNA

Journal Article.  5729 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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