Email updates

Keep up to date with the latest news and content from BMC Plant Biology and BioMed Central.

Open Access Research article

Triparental origin of triploid onion, Allium × cornutum (Clementi ex Visiani, 1842), as evidenced by molecular, phylogenetic and cytogenetic analyses

Željana Fredotović1, Ivica Šamanić1, Hanna Weiss-Schneeweiss2, Juraj Kamenjarin1, Tae-Soo Jang2 and Jasna Puizina1*

Author Affiliations

1 Department of Biology, University of Split, Faculty of Science, Teslina 12, 21000 Split, Croatia

2 Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria

For all author emails, please log on.

BMC Plant Biology 2014, 14:24  doi:10.1186/1471-2229-14-24

Published: 13 January 2014

Abstract

Background

Reconstruction of the parental origins of cultivated plants from wild relatives, especially after long periods of domestication, is not a trivial task. However, recent advances in molecular phylogenetics, among other approaches, have proved to be very informative in analyses of the origin and evolution of polyploid genomes. An established minor garden crop, triploid onion Allium × cornutum (Clementi ex Visiani, 1842) (2n = 3x = 24), is widespread in southeastern Asia and Europe. Our previous cytogenetic analyses confirmed its highly heterozygous karyotype and indicated its possible complex triparental genome origin. Allium cepa L. and Allium roylei Stearn were suggested as two putative parental species of A. × cornutum, whereas the third parental species remained hitherto unknown.

Results

Here we report the phylogenetic analyses of the internal transcribed spacers ITS1-5.8S-ITS2 of 35S rDNA and the non-transcribed spacer (NTS) region of 5S rDNA of A. × cornutum and its relatives of the section Cepa. Both ITS and NTS sequence data revealed intra-individual variation in triploid onion, and these data clustered into the three main clades, each with high sequence homology to one of three other species of section Cepa: A. cepa, A. roylei, and unexpectedly, the wild Asian species Allium pskemense B. Fedtsh. Allium pskemense is therefore inferred to be the third, so far unknown, putative parental species of triploid onion Allium × cornutum. The 35S and 5S rRNA genes were found to be localised on somatic chromosomes of A. × cornutum and its putative parental species by double fluorescent in situ hybridisation (FISH). The localisation of 35S and 5S rDNA in A. × cornutum chromosomes corresponded to their respective positions in the three putative parental species, A. cepa, A. pskemense, and A. roylei. GISH (genomic in situ hybridisation) using DNA of the three putative parental diploids corroborated the results of the phylogenetic study.

Conclusions

The combined molecular, phylogenetic and cytogenetic data obtained in this study provided evidence for a unique triparental origin of triploid onion A. × cornutum with three putative parental species, A. cepa, A. pskemense, and A. roylei.

Keywords:
Allium × cornutum; Allium cepa; Allium roylei; Allium pskemense; Triparental hybrid; Triploid; Fluorescence in situ hybridisation (FISH); ITS1-5.8S-ITS2; 5S rDNA non-transcribed spacer (NTS); Genomic in situ hybridisation (GISH)