Comparative cytogenetic mapping of chromosomes bearing rDNA sites in Passiflora subgenus Passiflora (Passifloracea)

Abstract

The genus Passiflora L. comprises around 500 species with different haploid numbers (n = 6, 9, 10 e 12) and variability in the number of ribosomal DNA sites (rDNA). The subgenus Passiflora Juss. is one of the most diverse and includes several species of economic importance, such as Passiflora edulis and Passiflora alata Curtis, as well as Passiflora watsoniana Mast., which is endemic to Northeastern Brazil. These three species present 2n = 18 and two (P. edulis, P. alata) or three (P. watsoniana) pairs of 35S rDNA sites. In P. edulis, these sites are located in chromosomes 7 and 8, identified by fluorescent in situ hybridization (FISH) with chromosome-specific bacterial artificial chromosomes (BACs). With the aim of investigating the conservation of synteny between these species, we used FISH with BACs 173B16 and 164M13, markers for chromosome 7 and 8, respectively, followed by FISH with rDNA. As previously observed in P. edulis, 35S rDNA sites were observed in opposite arms to the BAC markers of chromosome 7 and 8 of both, P. alata and P. watsoniana. In P. alata, the 35S rDNA was observed in the short arm of chromosome 7 and in the long arm of chromosome 8, as in P. edulis. In P. watsoniana, however, the 35S rDNA was located in the long arm of three chromosome pairs, two of them confirmed as chromosomes 7 and 8. The change between short and long arms in the chromosome 8 of P. watsoniana, as well as the presence of an extra rDNA site, is compatible with its phylogenetic distance and indicates karyotypic changes even among species with n = 9 in the Passiflora subgenus.

Financial support: CAPES, CNPq and FACEPE