engleski

Triparental origin of triploid onion Allium × cornutum (Clementi ex Visiani, 1842)

Triploid onion Allium × cornutum (Clementi ex Visiani, 1842) (2n = 3x = 24), is an established minor garden crop, widespread in southeastern Asia and Europe. The combined molecular, phylogenetic and cytogenetic data we obtained in our study provided evidence for its unique triparental genome origin. 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 wild relatives of the section Cepa showed clustering of the obtained sequences 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. A. pskemense is therefore inferred to be the third, so far unknown, putative parental species of triploid onion A. × cornutum. By application of double fluorescent in situ hybridisation (FISH) we localised the 35S and 5S rRNA genes on A. × cornutum chromosomes and their position largely corresponded to their respective positions in the three putative parental species. GISH (genomic in situ hybridisation) using DNAs of the three putative parental diploids enabled simultaneous visualization of the three genomes on somatic and meiotic chromosomes of the triploid onion. In order to identify the female parent of A. × cornutum, three different regions of the chloroplast genome (trnH-psbA, atpB-rbcL, and matK) were cloned and phylogenetically analyzed in A. x cornutum and its parental species. cpDNA sequences of the triploid showed the highest similarity to the A. cepa and A. roylei cpDNA indicating some of this or other closely related wild Allium species as a female progenitor of the triploid. PCR amplification and RFPL analysis of the selected genes from the chloroplast genome of A. × cornutum (accD, atpF and petB) allowed us to identify SNPs and indel typical for a unique male-sterile cytoplasm of onion, thus confirming that triploid hybrid onions harbour this unique type of cytoplasm, which is important for hybrid onion seed production.

triploid onions; ribosomal genes; chloroplast DNA; cpDNA; fluorescent in situ hybridisation FISH; genomic in situ hybridisation GISH

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