B chromosomes of Puschkinia libanotica are characterized by a reduced level of euchromatic histone H3 methylation marks

Abstract

Epigenetic marks in the chromosome complement of the liliaceous plant Puschkinia libanotica were studied using immunofluorescence to detect histone modifications. In particular, a comparison was made between the euchromatic and heterochromatic components of supernumerary B chromosomes (Bs) relative to the A chromosomes of the basic diploid set, in order to provide further insights into the enigmatic properties of these 'genetically silent' Bs. No differences were found between A and B chromosomes for the heterochromatic dimethylation marks of histone H3 at lysine positions 9 and 27. However, distinctions between A and B chromosomes were revealed for the euchromatic di- and trimethylation marks of histone H3 at lysine 4. The results indicate that the less-transcriptionally active Bs are not marked by an enriched level of heterochromatic histone marks, but rather by a low level of euchromatin-associated histone modifications.