Authors: Möller, Michael; Kokubugata, Goro; Jong, Kwiton
Publication: International Journal of Plant Science
Year: 2008
Genera: Aeschynanthus, Agalmyla, Streptocarpus

Fluorescent in situ hybridization is used to determine the number and position of 45S nuclear ribosomal DNA (45S‐nrDNA) clusters in members of the Gesneriaceae: Aeschynanthus, Agalmyla, and Streptocarpus (including Colpogyne, Hovanella, Saintpaulia, and Schizoboea). All sites detected are terminal in position. Species of Agalmyla analyzed are uniformly diploid and possess one 45S‐nrDNA locus per genome; those of Streptocarpus are diploid, with one or two loci per genome; and Aeschynanthus species are diploid or tetraploid, possessing one or two loci in each genome. In relating the nrDNA loci to the respective generic phylogenetic trees, contrasting patterns of 45S‐nrDNA locus evolution become apparent. In Streptocarpus, gain of loci is intragenomic, i.e., within haploid genomes, whereas in Aeschynanthus, it involves duplications by polyploidization as well as intragenomic changes. The latter appears to have occurred early in the diversification of the genus but relatively recently in Streptocarpus. The relevance of this investigation to the study of evolution of nrDNA loci is discussed.