Hypermethylation of CpNpG and CpG sequences flanking telomeres in the liverwort, Marchantia paleacea var. diptera

The level of cytosine methylation of nuclear DNAs from suspension-cultured cells and whole plants of the liverwort Marchantia paleacea var. diptera were investigated. Approximately 6 % of total cytosine was methylated in both cultured liverwort cells and whole plants. By digestion of nuclear DNA with methylation-insensitive and sensitive isoschizomers BstNI/EcoRII and MspI/HpaII followed by Southern blot analysis, hypermethylation at CpNpG and CpG sequences in the subtelomeric region was found in both sources. Addition of 5 mu M 5-azadeoxycytidine to suspension-cultured cells led to reduction of the initial methylation level by 80% and to considerable demethylation at CpNpG and CpG sequences in the subtelomeric region without inhibition of cell growth. These results are different from those from other lower plants, such as Chlamydomonas and fungi, of which nuclear DNA was hypomethylated.