Differential methylation of genes and retrotransposons facilitates shotgun sequencing of the maize genome

• Published in: Nature genetics Vol. 23; no. 3; pp. 305 - 308
• Main Authors: Martienssen, Robert A, Rabinowicz, Pablo D, Schutz, Kristin, Dedhia, Neilay, Yordan, Cristina, Parnell, Laurence D, Stein, Lincoln, McCombie, W. Richard
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 01.11.1999
• Subjects: Biological and medical sciences; Cloning, Molecular - methods; DNA Methylation; DNA Restriction Enzymes - metabolism; Escherichia coli - genetics; Fundamental and applied biological sciences. Psychology; Genes, Plant - genetics; Genes. Genome; Genome, Plant; Genomic Library; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Nucleic Acid Hybridization; Retroelements - genetics; Sequence Analysis, DNA - methods; Sequence Homology, Nucleic Acid; Zea mays; Zea mays - genetics; Retrotransposon; Monocotyledones; Zea mays; Nucleotide sequence; Repeated sequence; Transposable element; Method; Cereal crop; Gene; Gramineae; Angiospermae; Spermatophyta; Genome; Methylation; Sequencing
• ISSN: 1061-4036; 1546-1718
• DOI: 10.1038/15479

The genomes of higher plants and animals are highly differentiated, and are composed of a relatively small number of genes and a large fraction of repetitive DNA. The bulk of this repetitive DNA constitutes transposable, and especially retrotransposable, elements. It has been hypothesized that most of these elements are heavily methylated relative to genes, but the evidence for this is controversial. We show here that repeat sequences in maize are largely excluded from genomic shotgun libraries by the selection of an appropriate host strain because of their sensitivity to bacterial restriction-modification systems. In contrast, unmethylated genic regions are preserved in these genetically filtered libraries if the insert size is less than the average size of genes. The representation of unique maize sequences not found in plant reference genomes is also greatly enriched. This demonstrates that repeats, and not genes, are the primary targets of methylation in maize. The use of restrictive libraries in genome shotgun sequencing in plant genomes should allow significant representation of genes, reducing the number of reactions required.