Ty1/copia- and Ty3/gypsy-like DNA sequences in Helianthus species

Abstract

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.

Occurrence and chromosome distribution of retroelements and NUPT sequences in Copaifera langsdorffii Desf. (Caesalpinioideae)

“…The fragment of Ty3-gypsy-like retroelements cloned, labeled, and used in FISH produced signals that were scattered throughout the chromosomes and accumulated also in heterochromatic regions, including the cp-rDNA-like/GCrich. The Ty1-copia-and Ty3-gypsy-like retroelements comprise a very common and heterogeneous retroelement group in the plant kingdom (Flavell et al 1992;Todorovska 2007) and, in general, are found dispersed throughout chromosomes (Santini et al 2002) or grouped in specific regions (Belyayev et al 2001).…”

What transposable elements tell us about genome organization and evolution: the case of <i>Drosophila</i>

“…The same could be true for any genome even if the fact that we have its entire DNA sequence gives us the illusion that we know all about it. Although many TE families in Drosophila and plants are found in both euchromatin and heterochromatin, some are preferentially located in heterochromatin, where they can be found in clusters, and others mainly in euchromatin (Dimitri, 1997;Di Franco et al, 1997;Terrinoni et al, 1997;Santini et al, 2002;Alonso-Gonzalez et al, 2003). It is therefore suggested that the higher the fraction of copies of a given element in heterochromatin, the older the invasion of the genome by this TE.…”

Distribution of a Ty3/gypsy-like retroelement on the A and B-chromosomes of Cestrum strigilatum Ruiz & Pav. and Cestrum intermedium Sendtn. (Solanaceae)

“…Besides this general dispersed tendency, both species exhibited a concentration of these elements in some terminal regions, associated with NORs, which are also associated with GC-rich heterochromatin (Fregonezi et al, 2004). Retroelements have previously been reported to be associated with the NORs of some Triticeae (Belyayev et al, 2001), with the heterochromatin of Allium cepa (onion) (Pearce et al, 1996) and A. thaliana , and with centromeric regions in several monocotyledons (Kumar and Bennetzen, 1999) and dicotyledons (Santini et al, 2002). Retrotransposons have also been reported to be associated with the whole genome as segments dispersed along the A-and D-chromosomes of Avena sativa (oat) (Linares et al, 2001).…”