Organization of the 5s rDNA intergenic spacer of Quercus rubra L. and its relationship to the ukrainian Quercus species

Abstract

Aim. Quercus rubra L. is a representative of the North American section Lobatae, which has naturalized in Ukraine and becomes an invasive species in some places. Accordingly, elucidation of its relationship with the Ukrainian species of section Quercus is relevant to assess the possibility of interspecific hybridization. The 5S rDNA intergenic spacer (IGS) represents a convenient molecular marker to address this question. Methods. DNA isolation, PCR amplification, cloning and sequencing. Results. The IGS of Q. rubra was cloned and sequenced. It was shown that after the divergence of the Lobatae and Quercus sections, the IGS sequences evolved mainly by accumulation of nucleotide substitutions. A high level of IGS similarity was found for species within the Labatae and Quercus sections, while the genetic distances between the representatives of these two sections appeared significantly higher. Conclusions. The high level of nucleotide substitutions indicates a considerable genetic distance between the Lobatae and Quercus sections and calls into question the possibility of spontaneous hybridization between Q. rubra and Ukrainian native species of the section Quercus. At the same time, the close genetic relationship between other North American species, Q. lobata and Ukrainian "white oaks" indicate that introduction of representatives of this group may create conditions for their spontaneous crossing with the native species, which could be undesirable for the conservation of Ukraine's natural forest-steppe communities. Sequencing of the 5S rDNA IGS can be used for molecular genotyping of the Quercus species and for identification of interspecific hybrids.
 Keywords: 5S rDNA, molecular evolution, Quercus, Lobatae.