DEVELOPMENTAL ABNORMALITIES AND EPIMUTATIONS ASSOCIATED WITH DNA HYPOMETHYLATION MUTATIONS

A number of aberrant morphological phenotypes were noted during propag ation of the Arabidopsis thaliana DNA hypomethylation mutant, ddm1, by repeated self-pollination, Onset of a spectrum of morphological abnor malities, including defects in leaf structure, flowering time, and flo wer structure, was strictly associated with the ddm1 mutations, The mo rphological phenotypes arose at a high frequency in selfed ddm1 mutant lines and some phenotypes became progressively more severe in advanci ng generations. The transmission of two common morphological trait syn dromes in genetic crosses demonstrated that the phenotypes are caused by heritable lesions that develop in ddm1 mutant backgrounds, Loss of cytosine methylation in specific genomic sequences during the selfing regime was noted in the ddm1 mutants. Potential mechanisms for formati on of the lesions underlying the morphological abnormalities are discu ssed.