Copia and Gypsy retrotransposons: activity in sunflower and related species.

Retrotransposons are the prevalent and ubiquitous class of repetitive DNA sequences and constitute the bulk of the eukaryote genomes. The peculiar ability to move in different chromosomal location makes them part of the so-called mobile DNA, discovered by Barbara McClintock sixty years ago. During eukaryotic genome evolution, retrotransposons showed up the bias to invade the host genome via an effective replicative “copy and paste” mechanism based on an RNA intermediate. This RNA encodes enzymes committed to the retrotranscription and the integration back in the genome of a double stranded DNA daughter copy. As a consequence, retrotransposon are repeated and widespread in the genome of eukaryotes. Such features have allowed the developing of reliable molecular marker tools during last decade. One of these tools, to be used for LTR-retrotransposons, that display at 5’- and 3’-ends two long terminal repeats and are the most frequent class in plants, is the IRAP (Inter-Retrotransposon Amplified Polymorphism) protocol. It has been applied to study genetic variability in thirty-six wild accessions, twenty-six cultivars of sunflower (Helianthus annuus L.) and in thirty-nine species belonging to the genus Helianthus. Retrotransposon transcriptional and post-transcriptional activity have been also investigated by means of RT-PCR experiments and polymorphisms analysis in sunflower. Experiments indicate that Helianthus annuus genome harbours active retrotransposons, on the other hand their activity is controlled by the host to prevent hazardous effects due to retroposition, an event that occurred in the past and made retrotransposon proliferation responsible of a large genetic variability both at interspecific and intraspecific level.