title: The chromosomal distributions of Ty1-copia group retrotransposable elements in higher plants and their implications for genome evolution.
abstract: Retrotransposons make up a major fraction--sometimes more than 40%--of all plant genomes investigated so far. We have isolated the reverse transcriptase domains of the Ty1-copia group elements from several species, ranging in genome size from some 100 Mbp to 23,000 Mbp, and determined the distribution patterns of these retrotransposons on metaphase chromosomes and within interphase nuclei by DNA:DNA in situ hybridization. With some exceptions, the reverse transcriptase domains were distributed over the length of the chromosomes. Exclusion from rDNA sites and some centromeres (e.g., slash pine, 23,000 Mbp, or barley, 5500 Mbp) is frequent, whereas many species exclude retrotransposons from other sites of heterochromatin (e.g., intercalary and centromeric sites in broad bean). In contrast, in the plant Arabidopsis thaliana, widely used for plant molecular genetic studies because of its small genome (c. 100 Mbp), the Ty1-copia group reverse transcriptase gene domains are concentrated in the centromeric regions, colocalizing with the 180 bp satellite sequence pAL1. Unlike the pAL1 sequence, however, the Ty1-copia signal is also detectable as weaker, diffuse hybridization along the lengths of the chromosomes. Possible mechanisms for evolution of the contrasting distributions are discussed. Understanding the physical distribution of retrotransposons and comparisons of the distribution between species is critical to understanding their evolution and the significance for generation of the new patterns of variability and in speciation.
authors.affiliation: John Innes Centre Norwich, UK.
authors.forename: J S
authors.initials: JS
authors.lastname: Heslop-Harrison
authors.forename: A
authors.initials: A
authors.lastname: Brandes
authors.forename: S
authors.initials: S
authors.lastname: Taketa
authors.forename: T
authors.initials: T
authors.lastname: Schmidt
authors.forename: A V
authors.initials: AV
authors.lastname: Vershinin
authors.forename: E G
authors.initials: EG
authors.lastname: Alkhimova
authors.forename: A
authors.initials: A
authors.lastname: Kamm
authors.forename: R L
authors.initials: RL
authors.lastname: Doudrick
authors.forename: T
authors.initials: T
authors.lastname: Schwarzacher
authors.forename: A
authors.initials: A
authors.lastname: Katsiotis
authors.forename: S
authors.initials: S
authors.lastname: Kubis
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: S R
authors.initials: SR
authors.lastname: Pearce
authors.forename: A J
authors.initials: AJ
authors.lastname: Flavell
authors.forename: G E
authors.initials: GE
authors.lastname: Harrison
mesh_terms: D002874:Chromosome Mapping; D019143:Evolution, Molecular; D018745:Genome, Plant; D017403:In Situ Hybridization; D010944:Plants / Q000235:genetics*; D016133:Polymerase Chain Reaction; D012091:Repetitive Sequences, Nucleic Acid; D018626:Retroelements / Q000235:genetics*
chemical_list: D018626:Retroelements