Comparative chromosomal localization of 45S and 5S rDNAs and implications for genome evolution inCucumis

Abstract

Ribosomal DNAs are useful cytogenetic markers for chromosome analysis. Studies investigating site numbers and distributions of rDNAs have provided important information for elucidating genome organization and chromosomal relationships of many species by fluorescence in situ hybridization. But relevant studies are scarce for species of the genus Cucumis, especially in wild species. In the present study, FISH was conducted to investigate the organization of 45S and 5S rDNA among 20 Cucumis accessions, including cultivars and wild accessions. Our results showed that the number of 45S rDNA sites varied from one to five pairs in different accessions, and most of these sites are located at the terminal regions of chromosomes. Interestingly, up to five pairs of 45S rDNA sites were observed in C. sativus var. sativus, the species which has the lowest chromosome number, i.e., 2n = 14. Only one pair of 5S rDNA sites was detected in all accessions, except for C. heptadactylus, C. sp, and C. spp that had two pairs of 5S rDNA sites. The distributions of 5S rDNA sites showed more variation than 45S rDNA sites. The phylogenetic analysis in this study showed that 45S and 5S rDNA have contrasting evolutionary patterns. We find that 5S rDNA has a polyploidizationrelated tendency towards the terminal location from an interstitial location but maintains a conserved site number, whereas the 45S rDNA showed a trend of increasing site number but a relatively conserved location.

Adding color to a century‐old enigma: multi‐color chromosome identification unravels the autotriploid nature of saffron (Crocus sativus) as a hybrid of wild Crocus cartwrightianus cytotypes

“…This is underpinned by higher rates of unreduced pollen compared with unreduced eggs in many plant species (Ramsey & Schemske, ). It is conceivable that the remaining chromosomes 1.3 and 2.3 are present in the highly heterozygous C. cartwrightianus gene pool. We propose four losses of 18S‐5.8S‐25S rRNA gene arrays from C. cartwrightianus accessions similar or identical to Evia plant 2, Evia plant 5 and Attica 4 ZN 519, which resulted in saffron chromosomes 5.2, 6.3, 7.1 and 7.2. Chromosomal variability of rDNA sites has been frequently described in plants (Schmidt et al ., ; Zhang et al ., ; Garcia et al ., ). Most importantly, so‐called jumping nucleolus organizing regions have been reported in Allium cepa , like saffron a member of the Asparagales order (Schubert & Wobus, ).…”

Comparative Chromosomal Localization of 45S and 5S rDNA Sites in 76 Purple-Fleshed Sweet Potato Cultivars

“…FISH can not only identify the position of a target sequence but also perform its qualitative and relative quantitative analysis by combining labeled nucleic acid probes with chromosomes, interphase nucleus, or DNA fibers. It has been widely used for identifying specific chromosome regions, analyzing their composition, spatial location, and dynamic chromatin changes during the cell cycle [13][14][15]. Additionally, it has been widely used in unraveling the physical map, structure, and evolution of the genome and in analyzing the relationship between species [16][17][18][19][20][21].…”

An improved method for inducing prometaphase chromosomes in plants

“…Prometaphase chromosomes in Brassica [ 5 ] and rice [ 7 ] have been successfully induced using ethanol and acetic acid (3:1) without pretreatment. Other methods to accumulate metaphase and prometaphase chromosomes, such as with ice water (ice) treatment for 24 h [ 11 ] or 0.002 M 8-hydroxyquinoline (8-Hq) [ 12 , 13 ] have also been reported. Although FISH studies have also been reported in melon [ 12 – 15 ], most of them used metaphase chromosomes, which are shorter and more compact than prometaphase chromosomes.…”