RNA-directed de novo methylation of genomic sequences in plants

Abstract

One monomeric and three oligomeric potato spindle tuber viroid (PSTVd) cDNA units were introduced into the tobacco genome via the Agrobacterium-mediated leaf-disc transformation. Southern analysis of the integrates revealed that only their PSTVd-specific sequences become fully methylated, whereas the flanking T-DNA and the genomic plant DNA remain unaltered. Viroid cDNA methylation could only be observed after autonomous viroid RNA-RNA replication had taken place in these plants. These findings demonstrate that a mechanism of de novo methylation of genes might exist that can be induced and targeted in a sequence-specific manner by their own mRNA.