Scheme of the system to detect inhibition of cytosine methylation. Petunia plant line C002, which has transcriptionally silenced CHS-A transgenes, has been generated through spontaneous epigenetic changes involving cytosine methylation on CaMV 35S promoter (left; ref. ). N. benthamiana plants that have a transcriptionally silenced GFP gene were produced through virus-induced RNA-directed DNA methylation of the CaMV 35S promoter (right; ref. ). Seeds of these plants were sown on a medium that contained a potential demethylating agent. If the agent is inhibitory of cytosine methylation, the frequency of cytosine methylation in the promoters is reduced, resulting in the restoration of transcription from the promoters.