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 we re investigated. Approximately 6 % of total cytosine was methylated in both cultured liverwort cells and whole plants. By digestion of nuclear DNA wit h methylation-insensitive and sensitive isoschizomers BstNI/EcoRII and MspI /HpaII followed by Southern blot analysis, hypermethylation at CpNpG and Cp G 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 a t 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.