Amount and organization of the heterochromatin in Olea europaea and related species

Abstract

The amount and spatial organization of the heterochromatin in nuclei of the shoot meristem and the frequency in the nuclear DNA of sequences belonging to a family of tandem repeats were investigated in cultivars of Olea europaea and related species. Significant differences between Olea species and between cultivars of O. europaea were observed: (i) in the spatial organization of the heterochromatin in interphase nuclei as determined by the number and surface area of the chromocentres; (ii) in genome size; and (iii) in the amount of condensed chromatin as measured by cytophotometry carried out at different thresholds of optical density. DNA elements belonging to a family of tandem repeats about 80 bp in length (OeTaq80 repeats) were isolated from the genomic DNA of an olive cultivar. It was shown: (i) by nucleotide sequence comparisons, that these repeats display variability in structure even within the same array, where different elements may share no more than 74% homology; (ii) by in situ hybridization, that OeTaq80-related DNA sequences are mainly localized in the heterochromatin at the chromosome ends; (iii) by dot-blot hybridization experiments, that these sequences are highly represented in the genome of all the olive cultivars and the majority of Olea species studied, and that their frequency may differ significantly even between olive cultivars; and (iv) by calculating the copy number of OeTaq80-related sequences per haploid (1C) genome, that the redundancy of these DNA elements may differ significantly between the genomes tested. It is suggested that the inter- and intraspecific changes in the nuclear and genomic traits observed can contribute to the understanding of the phylogenetic relationships between Olea species and in defining parameters to be exploited in varietal identification within cultivated olives.

The Peculiar Landscape of Repetitive Sequences in the Olive (Olea europaea L.) Genome

“…5). The first three families (Oe80, Oe178, and Oe86) correspond to the OeTaq80, OeTaq178, and OeGEM86 families described by Bitonti et al (1999) and Minelli et al (2000) and account for ∼72% of tandem repeats. The fourth family (Oe179) was for the first time identified in this survey: it represents 12.6% of the tandem repeats and the most common repeat unit is 179-bp long; within this family, a number of repeats resulted truncated, with a variable length.…”

“…Olive ( Olea europaea L.) has a medium-sized haploid genome of 1.4–1.5 Gb (Loureiro et al 2007). Concerning repeated sequences, the best characterized are four tandem repeats isolated from genomic libraries and, in some instances, localized by cytological hybridization on olive chromosomes (Katsiotis et al 1998; Bitonti et al 1999; Minelli et al 2000; Lorite et al 2001; Contento et al 2002). Also putative retrotransposon fragments have been isolated and sequenced (Stergiou et al 2002; Natali et al 2007), but a comprehensive picture of repeat elements landscape in the olive genome is still lacking.…”

Chromosome Pairing and Chiasma Formation in Some Olive (Olea europaea L.) Cultivars of Iran

“…As a result, a great number of varieties are present in all the countries where this species is cultivated, raising several problems for germplasm management and preservation. Evaluation and characterization of olive genetic resources is therefore crucial.In general very little work is available about olive cytogenetics (Bitonti et al 1999, Minelli et al 2000 and as a result of shortage of knowledge on the olive genome, there is controversy about olive phylogeny and its relationship to its related wild forms (Zohary 1994, Bitonti et al 1999.Olive cultivars are grown in different parts of Iran and cultivation of the same cultivars for long period of time may lead to the genetic erosion confining the subsequent breeding programs. Therefore it is necessary to study the available diversity and introduce new variability as well.…”

“…In general very little work is available about olive cytogenetics (Bitonti et al 1999, Minelli et al 2000 and as a result of shortage of knowledge on the olive genome, there is controversy about olive phylogeny and its relationship to its related wild forms (Zohary 1994, Bitonti et al 1999.…”

Fruit Germplasm Characterization: Genomics Approaches for the Valorisation of Genetic Diversity

“…Varieties are predominantly diploid (2n = 2x = 46) (Minelli et al, 2000). The DNA content is 2.2 pg per 1C nucleus (Bitonti et al, 1999), correspondent to a genome size of 2.2 Gbp (De la Rosa et al, 2003).…”