Characteristics Of DNA Constitution And Epigenetic Changes In B Chromosomes Of Rye (Secale Cereale L.)

B chromosomes (Bs) are also called supernumerary chromosomes, accessorychromosomes or extra chromosomes. They are supernumerary to the standardchromosomes (A chromosomes) set, which are found in thousands of plants and animals.They are often morphologically distinct from A chromosomes, being smaller and morehighly heterochromatic in most cases. B chromosomes do not pair with A chromosomes,they are inherited in a non-Mendelian way, exhibiting meiotic and mitotic instability andnondisjunction. Bs have little influence with the phenotype.DNA sequence differences in rye genomes (JNK population with similar geneticbackground) with and without B chromosomes were analyzed by random amplifiedpolymorphic DNA (RAPD). There were some bands which both appeared in 0B and +Bgenomes, but some appeared in +B genome only. Southern blot were performed afterprobing the sequences. There were hybridized signals in both genomes with the probefrom A/B chromosomes, while a few siginals in 0B genome with the probe from Bchromosomes only. Though some B chromosome specific DNA were existed, they weresimilar with the A chromosomes to a certain extent. Our results showed that Bchromosome DNA is quite identical to the corresponding sequence of A chromosome. Bchromosome DNA has the common character of A chromosome. The results werevaluble for the explanation of the origin and evolution of B chromosomes.After RAPD amplification, 5 out of 100 arbitrary 10-met primers were screened out,following coupled restriction enzyme digestion and random amplification (CRED-RA) ofgenomic DNA to detect cytosine methylation changes in genomes with and without Bchromosomes. That is, prior to PCR amplification, genomic DNA were digested with apair of methylation isoschizomers (Hpaâ…¡and Mspâ… ) which recognize the samerestriction site (CCGG) but have different sensitivities to cytosine methylation. AfterPCR amplification, the products were re-digested with the same pair of restrictionendonucleases. DNA methylation was identified by comparing the banding patterns oftemplate DNA amplified without restriction, template DNA amplified after restrictionand product DNA restricted after amplification. The results showed that most of the sequences from genomes with B chromosomes were similar with those from genomeswithout B chromosomes, implying the possible similarity of DNA sequences on both Aand B chromosomes. DNA methylation (C~mCGG and ~mC~mCGG) was observed in bothgenomes with and without B chromosomes. Moreover, genomes with B chromosomescause extensive DNA methylation (C~mCGG) comparing with those without Bchromosomes. These epigenetic changes may play a key role in the phenotypicsuppression or gene silencing caused by B chromosome.