Abstract
In eukaryotes, 45S rRNA genes are arranged in tandem arrays of repeat units, and not all copies are transcribed during mitosis. DNA methylation is considered to be an epigenetic marker for rDNA activation. Here, we established a clear and accurate karyogram for Jatropha curcas L. The chromosomal formula was found to be 2n = 2x = 22 = 12m+10sm. We found that the 45S rDNA loci were located at the termini of chromosomes 7 and 9 in J. curcas. The distribution of 45S rDNA has no significant difference in J. curcas from different sources. Based on the hybridization signal patterns, there were two forms of rDNA - dispersed and condensed. The dispersed type of signals appeared during interphase and prophase, while the condensed types appeared during different stages of mitosis. DNA methylation analysis showed that when 45S rDNA stronger signals were dispersed and connected to the nucleolus, DNA methylation levels were lower at interphase and prophase. However, when the 45S rDNA loci were condensed, especially during metaphase, they showed different forms of DNA methylation.
Highlights
In higher eukaryotes, the ribosomal RNA genes comprising the 18S-5.8S-26S rDNA (45S rDNA) loci are generally referred to the nucleolar organizer regions (NORs)
In Type III, the 45S rDNA of one pair were methylated in telomeric region,which had stronger fluorescence in situ hybridization (FISH) signals (Figure 5B, indicated by yellow arrows)
Karyotype Analysis is Important for the Physical Localization of the 45S rDNA Loci in J. curcas
Summary
The ribosomal RNA genes comprising the 18S-5.8S-26S rDNA (45S rDNA) loci are generally referred to the nucleolar organizer regions (NORs). Studies of repetitive sequences are useful to investigate chromosome evolution between plant species [3,4]. The physical localization of 45S rDNA loci have been studied in maize [5,6], wheat [7], peanut [8], rice [9,10], pine [4], Nymphaea [11], the Orchidaceae [12], and many other species. Unmethylated or hypomethylated DNA and histone H3 lysine 4 methylation (H3K4me) are considered to be epigenetic markers for euchromatin, and are responsible for rDNA activation [13,14], whereas hypermethylated DNA and histone H3K9 methylation are indicative of rDNA gene silencing. The most widely studied epigenetic modification is DNA methylation, which mediates gene silencing [18,19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
