Investigations of 5S rDNA of Vitis vinifera L.: sequence analysis and physical mapping.

Here we report the first results of a study of 5S rDNA of Vitis vinifera. 5S rDNA sequences from seven genotypes were amplified by PCR, cloned, and sequenced. Three types of repeats were found. Two variants, denominated long repeat and short repeat, appeared to be the main components of the 5S rDNA of this species, since they were found in all genotypes analyzed. They differed markedly from each other in both the length and the nucleotide composition of the spacers. The third variant, classified as DEL short repeat, differs from the short repeat owing to a large deletion in the spacer region. It appears to be the most recent repeat type, since it was identified in only one genotype. The organization of the 5S rDNA repeat unit variants was investigated by amplifying the genomic DNA with primers designed on the sequence of the long and short spacers. The PCR-amplified fragments showed that the long repeat is associated with the other two repeats, indicating that in V. vinifera different repeat units coexist within the same tandem array. FISH analysis demonstrated that 5S rRNA genes are localized at a single locus. The variability of 5S rDNA repeats is discussed in relation to the putative allopolyploid origin of V. vinifera.