DNA methylation patterns of Melandrium album chromosomes

Melandrium album (syn. Silene latifolia) belongs to dioecious plant species possessing heteromorphic sex chromosomes, X and Y. Our previous experiment s using in situ nick translation and replication kinetics analysis indicate d structural and functional differences between the two X chromosomes in ho mogametic female cells. Here we show DNA methylation patterns of M. album r oot tip chromosomes using the indirect immunofluorescence approach with a m onoclonal antibody raised against 5-methylcytosine (5-mC). In male cells, a more intensive 5-mC labelling on the shorter arm of the only X chromosome was observed in comparison with the longer X arm. A global hypermethylation of the male Y chromosome was not found, which indicates its prevalent euch romatic character. In female cells, the specific 5-mC pattern of the X chro mosome was found on a single X chromosome, whereas the other X displayed an overall higher level of 5-mC labelling. Application of a hypomethylating d rug, 5-azacytidine (5-azaC), during seed germination led to a deletion of a ny specific differences in the 5-mC distribution between the two X chromoso mes. Confocal laser scanning microscopy analysis of DNA methylation in inte rphase nuclei showed hypermethylated domains that were efficiently deconden sed and hypomethylated by 5-azaC treatment. The presented data show reprodu cible differences in the DNA methylation patterns between the two X chromos omes in M. album female somatic cells, which indicate their distinct transc riptional activities as a possible consequence of the negative dosage compe nsation of X-linked genes.