title: Ribosomal DNA evolution and phylogeny in Aloe (Asphodelaceae).
abstract: All Aloe taxa (∼400 species) share a conserved bimodal karyotype with a basic genome of four large and three small submetacentric/acrocentric chromosomes. We investigated the physical organization of 18S-5.8S-26S and 5S ribosomal DNA (rDNA) using fluorescent in situ hybridization (FISH) to 13 Aloe species. The organization was compared with a phylogenetic tree of 28 species (including the 13 used for FISH) constructed by sequence analysis of the internal transcribed spacer (ITS) of 18S-5.8S-26S rDNA. The phylogeny showed little divergence within Aloe, although distinct, well-supported clades were found. FISH analysis of 5S rDNA distribution showed a similar interstitial location on a large chromosome in all species examined. In contrast, the distribution of 18S-5.8S-26S rDNA was variable, with differences in number, location, and size of loci found between species. Nevertheless, within well-supported clades, all species had the same organizational patterns. Thus, despite the striking stability of karyotype structure and location of 5S rDNA, the distribution of 18S-5.8S-26S rDNA is not so constrained and has clearly changed during Aloe speciation.
authors.affiliation: School of Biological Sciences, Queen Mary and Westfield College, University of London, E1 4NS, UK; and.
authors.forename: S P
authors.initials: SP
authors.lastname: Adams
authors.forename: I J
authors.initials: IJ
authors.lastname: Leitch
authors.forename: M D
authors.initials: MD
authors.lastname: Bennett
authors.forename: M W
authors.initials: MW
authors.lastname: Chase
authors.forename: A R
authors.initials: AR
authors.lastname: Leitch