Heteroplasmy and nuclear copies of mitochondrial genes (NUMTs) identified in the zone of introgressive hybridization of Norway spruce and Siberian spruce

Studies of possible post-glacial migrations and the processes of formation of areas of coniferous species are of particular interest from the point of view of forest genesis. Molecular markers are effectively used to study the phylogeography of forest-forming species. In this study, for spruces growing in the Native Forest Reserve 'Vepssky Forest', heterogeneous amplification products of the second intron of the nad1 mitochondrial gene were obtained by PCR with gene-specific primers. By the analysis of the PCR products it has been established that they correspond to mtDNA sequences previously considered species-specific for Picea abies and P. obovata and are simultaneously amplified using DNA of the same tree. The revealed heterogeneity can be explained by two reasons: mtDNA heteroplasmy or amplification of nuclear copies of mitochondrial genes (NUMT). In order to establish and explain the nature of the detected heterogeneity, the methodological approaches previously used for similar studies in birds and mammals, such as cloning and sequencing of PCR products, amplification of large mtDNA fragments (Long range PCR) and phylogenetic analysis, were used. The obtained results testify in favor of heteroplasmy, which can be considered as a historical trace of close contact between P. abies and P. obovata in the area of the Vepsovskaya Upland in the northwest of the East (NUMTs) European Plain. The presence of the P. obovata-specific haplotype of the nad1 mitochondrial gene in the spruces of the East European Plain is described for the first time. In conifers, the phenomenon of heteroplasmy is described for the zone of introgressive hybridization of closely related species. Nuclear pseudogenes of mitochondrial origin (NUMTs), similar in sequence to the mitochondrial haplotype of the nad1 gene, have been described for the first time for European spruce.

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