Physical mapping of 5S and 45S rDNA genes and ploidy levels of Iranian Asparagus species

Abstract

Twelve asparagus accessions collected from natural regions of Iran were analyzed by flow cytometry to assess their ploidy level. These accessions belong to both cultivated and wild species (A. officinalis, A. persicus, A. breslerianus, A. verticillatus) from the Asparagus subgenus (x=10). Different ploidy levels (diploid, tetraploid, octoploid and decaploid) were found in A. officinalis. Likewise flow cytometry analysis showed a diploid level for A. persicus and A. verticillatus whereas an octoploid level was obtained in A. breslerianus. Decaploid and octoploid levels have been reported in A. officinalis and A. breslerianus for the first time in this study. These results suggest that polyploidization may have played an important role in the evolution of the Asparagus genus. FISH technique was employed to study the physical localization of the rDNA genes (45S and 5S). One accession of each wild species and ploidy level were used. One rDNA 5S signal per genome was obtained in all 6 accessions whereas the number of rDNA 45S signals ranged from two (A. persicus, A. verticillatus) to three (A. officinalis, A. breslerianus). Furthermore, in A. persicus and A. officinalis (tetraploid and octoploid accessions) all the rDNA 5S and 45S signals were located in different chromosomes. On the contrary, A. officinalis (diploid accession) and A. verticillatus genomes showed one chromosome carrying both rDNA signals. In conclusion, FISH analysis revealed that the pattern of signals obtained with both rDNA probes was different among the genomes of the four species studied. Also, differences between accessions were found in A. officinalis.