The DNA methylation locusDDM1 is required for maintenance of gene silencing in Arabidopsis

These results indicate that methylation is necessary for maintenance of phosphoribosylanthranilate isomerase gene silencing and that intermediate levels of DNA methylation are associated with intermediate gene silencing

Jeffrey A. Jeddeloh; Judith Bender; Eric J. Richards

2008

Scholarcy highlights

  • To investigate the relationship between cytosine methylation and gene silencing in Arabidopsis, we constructed strains containing the ddm1 hypomethylation mutation and a methylated and silenced PAI2 tryptophan biosynthetic gene that results in a blue fluorescent plant phenotype
  • In this report we combine the Arabidopsis ddm1 DNA hypomethylation mutation with the MePAI2-silenced reporter gene to carry out a genetic analysis of methylation and silencing. ddm1 mutations cause an immediate loss of modification in repeated DNA when first made homozygous and foster a progressive loss of methylation in the low-copy portion of the genome over several generations of inbreeding
  • Inbreeding ddm1 mutants progressively extinguishes PAI2 silencing Because ddm1 mutations cause inbreeding-associated progressive DNA hypomethylation, we investigated the effect of inbreeding pai ddm1 mutants
  • Cytosine methylation is necessary for PAI2 gene silencing
  • Our findings address the relationship between DNA methylation and gene silencing, as well as the mode of action of Arabidopsis ddm1 DNA hypomethylation mutations
  • Hypermethylated alleles recovered from pai ddm1 mutant line C.1 and the nonfluorescent revertant control line REV2 do not violate the strict correlation between cytosine methylation and gene silencing because infrequent silenced, methylated alleles will be recessive to expressed alleles
  • Spontaneously hypomethylated nonfluorescent revertant lines generated from the fluorescent ⌬pai1–pai4 mutant do not segregate progeny that have returned to the methylated and silenced fluorescent state de novo at a detectable frequency even after several generations

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