title: The peculiar landscape of repetitive sequences in the olive (Olea europaea L.) genome.
abstract: Analyzing genome structure in different species allows to gain an insight into the evolution of plant genome size. Olive (Olea europaea L.) has a medium-sized haploid genome of 1.4 Gb, whose structure is largely uncharacterized, despite the growing importance of this tree as oil crop. Next-generation sequencing technologies and different computational procedures have been used to study the composition of the olive genome and its repetitive fraction. A total of 2.03 and 2.3 genome equivalents of Illumina and 454 reads from genomic DNA, respectively, were assembled following different procedures, which produced more than 200,000 differently redundant contigs, with mean length higher than 1,000 nt. Mapping Illumina reads onto the assembled sequences was used to estimate their redundancy. The genome data set was subdivided into highly and medium redundant and nonredundant contigs. By combining identification and mapping of repeated sequences, it was established that tandem repeats represent a very large portion of the olive genome (∼31% of the whole genome), consisting of six main families of different length, two of which were first discovered in these experiments. The other large redundant class in the olive genome is represented by transposable elements (especially long terminal repeat-retrotransposons). On the whole, the results of our analyses show the peculiar landscape of the olive genome, related to the massive amplification of tandem repeats, more than that reported for any other sequenced plant genome.
authors.affiliation: Department of Agricultural, Food, and Environmental Sciences, University of Pisa, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Barghini
authors.forename: Lucia
authors.initials: L
authors.lastname: Natali
authors.forename: Rosa Maria
authors.initials: RM
authors.lastname: Cossu
authors.forename: Tommaso
authors.initials: T
authors.lastname: Giordani
authors.forename: Massimo
authors.initials: M
authors.lastname: Pindo
authors.forename: Federica
authors.initials: F
authors.lastname: Cattonaro
authors.forename: Simone
authors.initials: S
authors.lastname: Scalabrin
authors.forename: Riccardo
authors.initials: R
authors.lastname: Velasco
authors.forename: Michele
authors.initials: M
authors.lastname: Morgante
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavallini
mesh_terms: D018744:DNA, Plant / Q000235:genetics*; D066264:Datasets as Topic; D018745:Genome, Plant / Q000502:physiology*; D031658:Olea / Q000235:genetics*; D018626:Retroelements; D020080:Tandem Repeat Sequences; D020079:Terminal Repeat Sequences
chemical_list: D018744:DNA, Plant; D018626:Retroelements
keywords: Olea europaea; assembly of NGS reads; genome landscape; repetitive DNA; retrotransposons; tandem repeats