Nuclear Ribosomal ITS1–5.8S rDNA-ITS2 Region as a Phylogenetic Marker for Selenicereus grandiflorus and Related Species (Cactaceae: Cactoideae: Phyllocacteae)

The nuclear ITS1–5.8S rDNA–ITS2 region is among the most widely used markers for phylogenetic studies in plants. We sequenced the ITS1–5.8S rDNA–ITS2 region in several species of Selenicereus, two species of Deamia and Epiphyllum chrysocardium. The newly generated sequences were found to be more closely related to ITS and 5.8S rDNA sequences from representatives of other cactus tribes than to the Selenicereus ITS sequences previously deposited in GenBank by research group O. Plume. Importantly, all these sequences retained three conserved motifs of the 5.8S rRNA gene that are commonly used to distinguish functional copies from pseudogenes. Then we analyzed available genome assemblies representing 12 species of Cactaceae. In contrast to the ribotypes identified in this study, the previously reported 5.8S rDNA variants in the assembled genomes of Selenicereus and Carnegiea were represented by a single copy flanked by highly degraded 18S and 28S rDNA sequences. Phylogenetic analyses based on the newly generated ITS sequences and Genbank data supported the monophyly of the subtribes Hylocereinae, Rhipsalideae, and Trichocereinae, as well as the tribes Rhipsalideae, Notocacteae, and Cylindropuntieae. These results demonstrate that the functional ITS1-5.8S rDNA–ITS2 region represents an informative marker for phylogenetic studies within the Cactaceae.