A DNA Methyltransferase Homolog With a Chromodomain Exists in Multiple Polymorphic Forms in Arabidopsis

A DNA Methyltransferase Homolog With a Chromodomain Exists in Multiple Polymorphic Forms in... Steven Henikoff a and Luca Comai b a Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024 b Department of Botany, University of Washington, Seattle, Washington 98195-5325 Corresponding author: Steven Henikoff, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. North, Seattle, WA 98109-1024, steveh@muller.fhcrc.org (E-mail). Communicating editor: V. S UNDARESAN Chromodomains are thought to mediate protein-protein interactions between chromatin components. We have detected a chromodomain embedded within the catalytic region of a predicted Arabidopsis DNA methyltransferase that is diverged from other eukaryotic enzymes. The 791 residue "chromomethylase" (CMT1) is encoded by a floral transcript that is spliced from 20 exons and is present at only ~1/10 -7 of total mRNA. Genomic sequencing reveals an ancient haplotype split at CMT1 between Col-0 + Metz and the other ecotypes examined. In the Col-0 + Metz haplotype, alternative mRNA processing at intron 13 truncates the coding region. In Ler, RLD, and No-0, similar truncation is caused by insertion of an intact retrotransposon, Evelknievel, which is present as a single copy in Ler and RLD and is currently methylated and inactive. Evelknievel is found at this site on a single branch that connects the Ler, RLD, and No-0 ecotypes but is absent from the genomes of all other ecotypes examined. A stop codon within exon 6 of the Metz ecotype confirms that CMT1 is nonessential. Nevertheless, comparison to CMT1 of Cardaminopsis arenosa , an outcrossing relative, indicates conservation for DNA methyltransferase function. We discuss how allelic diversity of CMT1 may reflect loosened selective constraints in a self-fertilizing species such as Arabidopsis thaliana. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Genetics Genetics Society of America

A DNA Methyltransferase Homolog With a Chromodomain Exists in Multiple Polymorphic Forms in Arabidopsis

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Abstract

Steven Henikoff a and Luca Comai b a Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024 b Department of Botany, University of Washington, Seattle, Washington 98195-5325 Corresponding author: Steven Henikoff, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. North, Seattle, WA 98109-1024, steveh@muller.fhcrc.org (E-mail). Communicating editor: V. S UNDARESAN Chromodomains are thought to mediate protein-protein interactions between chromatin components. We have detected a chromodomain embedded within the catalytic region of a predicted Arabidopsis DNA methyltransferase that is diverged from other eukaryotic enzymes. The 791 residue "chromomethylase" (CMT1) is encoded by a floral transcript that is spliced from 20 exons and is present at only ~1/10 -7 of total mRNA. Genomic sequencing reveals an ancient haplotype split at CMT1 between Col-0 + Metz and the other ecotypes examined. In the Col-0 + Metz haplotype, alternative mRNA processing at intron 13 truncates the coding region. In Ler, RLD, and No-0, similar truncation is caused by insertion of an intact retrotransposon, Evelknievel, which is present as a single copy in Ler and RLD and is currently methylated and inactive. Evelknievel is found at this site on a single branch that connects the Ler, RLD, and No-0 ecotypes but is absent from the genomes of all other ecotypes examined. A stop codon within exon 6 of the Metz ecotype confirms that CMT1 is nonessential. Nevertheless, comparison to CMT1 of Cardaminopsis arenosa , an outcrossing relative, indicates conservation for DNA methyltransferase function. We discuss how allelic diversity of CMT1 may reflect loosened selective constraints in a self-fertilizing species such as Arabidopsis thaliana.

Journal

GeneticsGenetics Society of America

Published: May 1, 1998

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