The karyotype of Adenia and the origin of the base number x = 12 in Passifloroideae (Passifloraceae).

Abstract

Adenia is an Old World genus of Passifloroideae closely related to Passiflora. The two genera comprise the large majority of Passifloroideae species, although most studies are concentrated on Passiflora. Cytological analyses reveal that changes in chromosome numbers played an important role in the evolution of Passiflora, whereas in the remaining genera little is known, hindering the identification of the base number of the family. Here we analyzed the chromosome number and the 35S rDNA sites of three species of Adenia and reevaluated the base number (x) of the subfamily Passifloroideae and the family Passifloraceae, including chromosome data for Turneroideae and Malesherbioideae. The chromosome number of Adenia species seemed to be stable with 2n = 24 or 48 and one or two pairs of rDNA sites, very similar to Passiflora subgenus Astrophea, suggesting a common ancestral karyotype with x = 12. Differently, Turneroideae and Malesherbioideae present x = 7. A whole genomic duplication detected after the separation of Passifloroideae and Malesherbioideae suggests that the base number of Passifloraceae most probably was x = 7, which by dysploidy and polyploidy generated x = 12 for the subfamily Passifloroideae.