We describe the isolation and characterization of two missense mutations in the cytosine-DNA-meth... more We describe the isolation and characterization of two missense mutations in the cytosine-DNA-methyl-transferase gene, MET1, from the flowering plant Arabidopsis thaliana. Both missense mutations, which affect the catalytic domain of the protein, led to a global reduction of cytosine methylation throughout the genome. Surprisingly, the met1-2 allele, with the weaker DNA hypomethylation phenotype, alters a well-conserved residue in methyltransferase signature motif I. The stronger met1-1 allele caused late flowering and a heterochronic delay in the juvenile-to-adult rosette leaf transition. The distribution of late-flowering phenotypes in a mapping population segregating met1-1 indicates that the flowering-time phenotype is caused by the accumulation of inherited defects at loci unlinked to the met1 mutation. The delay in flowering time is due in part to the formation and inheritance of hypomethylated fwa epialleles, but inherited defects at other loci are likely to contribute as well...
Proceedings of the National Academy of Sciences, 2008
Understanding how nutrients affect gene expression will help us to understand the mechanisms cont... more Understanding how nutrients affect gene expression will help us to understand the mechanisms controlling plant growth and development as a function of nutrient availability. Nitrate has been shown to serve as a signal for the control of gene expression in Arabidopsis . There is also evidence, on a gene-by-gene basis, that downstream products of nitrogen (N) assimilation such as glutamate (Glu) or glutamine (Gln) might serve as signals of organic N status that in turn regulate gene expression. To identify genome-wide responses to such organic N signals, Arabidopsis seedlings were transiently treated with ammonium nitrate in the presence or absence of MSX, an inhibitor of glutamine synthetase, resulting in a block of Glu/Gln synthesis. Genes that responded to organic N were identified as those whose response to ammonium nitrate treatment was blocked in the presence of MSX. We showed that some genes previously identified to be regulated by nitrate are under the control of an organic N-...
Proceedings of the National Academy of Sciences, 2002
Paramutation is an example of a non-Mendelian-directed allelic interaction that results in the ep... more Paramutation is an example of a non-Mendelian-directed allelic interaction that results in the epigenetic alteration of one allele. We describe a paramutation-like interaction between two alleles, bal and cpr1–1 ( constitutive expressor of PR genes 1 ), which map to a complex R -like gene cluster on Arabidopsis chromosome 4. Both alleles cause dwarfing and constitutive defense responses, similar to another dwarf variant, ssi1 ( suppressor of SA-insensitivity 1 ). Previous work has demonstrated that the bal and ssi1 phenotypes are caused by overexpression of an R -like gene from the cluster, which activates an salicylic acid-dependent defense pathway. Here, we show that the cpr1–1 variant does not alter gene expression from the R -like gene cluster. The bal and cpr1–1 alleles did not complement each other in F 1 hybrids, but F 2 populations that segregated bal and cpr1–1 alleles contained plants with normal morphology at a frequency of 20%. By using molecularly marked bal and cpr1–1 ...
Plant pathogen resistance is mediated by a large repertoire of resistance (R) genes, which are of... more Plant pathogen resistance is mediated by a large repertoire of resistance (R) genes, which are often clustered in the genome and show a high degree of genetic variation. Here, we show that anArabidopsis thaliana R-gene cluster is also subject to epigenetic variation. We describe a heritable but metastable epigenetic variant bal that overexpresses the R-like geneAt4g16890 from a gene cluster on Chromosome 4. The balvariant and Arabidopsis transgenics overexpressing theAt4g16890 gene are dwarfed and constitutively activate the salicylic acid (SA)-dependent defense response pathway. Overexpression of a related R-like gene also occurs in the ssi1(suppressor of SA insensitivity1) background, suggesting that ssi1 is mechanistically related to bal.
We describe the isolation and characterization of two missense mutations in the cytosine-DNA-meth... more We describe the isolation and characterization of two missense mutations in the cytosine-DNA-methyl-transferase gene, MET1, from the flowering plant Arabidopsis thaliana. Both missense mutations, which affect the catalytic domain of the protein, led to a global reduction of cytosine methylation throughout the genome. Surprisingly, the met1-2 allele, with the weaker DNA hypomethylation phenotype, alters a well-conserved residue in methyltransferase signature motif I. The stronger met1-1 allele caused late flowering and a heterochronic delay in the juvenile-to-adult rosette leaf transition. The distribution of late-flowering phenotypes in a mapping population segregating met1-1 indicates that the flowering-time phenotype is caused by the accumulation of inherited defects at loci unlinked to the met1 mutation. The delay in flowering time is due in part to the formation and inheritance of hypomethylated fwa epialleles, but inherited defects at other loci are likely to contribute as well...
Proceedings of the National Academy of Sciences, 2008
Understanding how nutrients affect gene expression will help us to understand the mechanisms cont... more Understanding how nutrients affect gene expression will help us to understand the mechanisms controlling plant growth and development as a function of nutrient availability. Nitrate has been shown to serve as a signal for the control of gene expression in Arabidopsis . There is also evidence, on a gene-by-gene basis, that downstream products of nitrogen (N) assimilation such as glutamate (Glu) or glutamine (Gln) might serve as signals of organic N status that in turn regulate gene expression. To identify genome-wide responses to such organic N signals, Arabidopsis seedlings were transiently treated with ammonium nitrate in the presence or absence of MSX, an inhibitor of glutamine synthetase, resulting in a block of Glu/Gln synthesis. Genes that responded to organic N were identified as those whose response to ammonium nitrate treatment was blocked in the presence of MSX. We showed that some genes previously identified to be regulated by nitrate are under the control of an organic N-...
Proceedings of the National Academy of Sciences, 2002
Paramutation is an example of a non-Mendelian-directed allelic interaction that results in the ep... more Paramutation is an example of a non-Mendelian-directed allelic interaction that results in the epigenetic alteration of one allele. We describe a paramutation-like interaction between two alleles, bal and cpr1–1 ( constitutive expressor of PR genes 1 ), which map to a complex R -like gene cluster on Arabidopsis chromosome 4. Both alleles cause dwarfing and constitutive defense responses, similar to another dwarf variant, ssi1 ( suppressor of SA-insensitivity 1 ). Previous work has demonstrated that the bal and ssi1 phenotypes are caused by overexpression of an R -like gene from the cluster, which activates an salicylic acid-dependent defense pathway. Here, we show that the cpr1–1 variant does not alter gene expression from the R -like gene cluster. The bal and cpr1–1 alleles did not complement each other in F 1 hybrids, but F 2 populations that segregated bal and cpr1–1 alleles contained plants with normal morphology at a frequency of 20%. By using molecularly marked bal and cpr1–1 ...
Plant pathogen resistance is mediated by a large repertoire of resistance (R) genes, which are of... more Plant pathogen resistance is mediated by a large repertoire of resistance (R) genes, which are often clustered in the genome and show a high degree of genetic variation. Here, we show that anArabidopsis thaliana R-gene cluster is also subject to epigenetic variation. We describe a heritable but metastable epigenetic variant bal that overexpresses the R-like geneAt4g16890 from a gene cluster on Chromosome 4. The balvariant and Arabidopsis transgenics overexpressing theAt4g16890 gene are dwarfed and constitutively activate the salicylic acid (SA)-dependent defense response pathway. Overexpression of a related R-like gene also occurs in the ssi1(suppressor of SA insensitivity1) background, suggesting that ssi1 is mechanistically related to bal.
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Papers by Trevor Stokes