A study in the model plant Arabidopsis thaliana shows that aging causes a loss of epigenetic integrity, leading to a breakdown of DNA methylation in heterochromatin.[1][4] This decay of methylation in the first true leaves gradually increases with tissue age and is accompanied by increased expression of transposon elements.[1][2] The rate of epigenetic aging can be influenced by increasing or decreasing the life span of the plant.[1] Apical meristems are protected from this senescence process.[1][2] A program of transcriptional repression suppresses pathways maintaining DNA methylation during aging.[1][4] Mutants of this mechanism show a complete absence of epigenetic decay.[1][2] New organs are epigenetically young and age independently of the rest of the plant.[2] The TCX5 and TCX6 genes act as regulatory switches that suppress the maintenance of methylation during aging.[2]