Cytological characterization of three closely related pines - Pinus mugo, P. uliginosa and P. × rhaetica from the Pinus mugo complex (Pinaceae)

Assessment of ITS2 Region Relevance for Taxa Discrimination and Phylogenetic Inference among Pinaceae

The internal transcribed spacer 2 (ITS2) is one of the best-known universal DNA barcode regions. This short nuclear region is commonly used not only to discriminate taxa, but also to reconstruct phylogenetic relationships. However, the efficiency of using ITS2 in these applications depends on many factors, including the family under study. Pinaceae represents the largest family of extant gymnosperms, with many species of great ecological, economic, and medical importance. Moreover, many members of this family are representatives of rare, protected, or endangered species. A simple method for the identification of Pinaceae species based on DNA is necessary for their effective protection, authentication of products containing Pinaceae representatives, or phylogenetic inference. In this study, for the first time, we conducted a comprehensive study summarizing the legitimacy of using the ITS2 region for these purposes. A total of 368 sequences representing 71 closely and distantly related taxa of the seven genera and three subfamilies of Pinaceae were characterized for genetic variability and divergence. Intra- and interspecies distances of ITS2 sequences as well as rates of sequence identification and taxa discrimination among Pinaceae at various taxonomic levels, i.e., the species complex, genus, subfamily, and family, were also determined. Our study provides a critical assessment of the suitability of the ITS2 nuclear DNA region for taxa discrimination among Pinaceae. The obtained results clearly show that its usefulness for this purpose is limited.

New Insight into Taxonomy of European Mountain Pines, Pinus mugo Complex, Based on Complete Chloroplast Genomes Sequencing

The Pinus mugo complex is a large group of closely related mountain pines, which are an important component of the ecosystems of the most important mountain ranges, such as the Alps, Carpathians and Pyrenees. The phylogenetic relationships between taxa in this complex have been under discussion for many years. Despite the use of many different approaches, they still need to be clarified and supplemented with new data, especially those obtained with high-throughput methods. Therefore, in this study, the complete sequences of the chloroplast genomes of the three most recognized members of the Pinus mugo complex, i.e., Pinus mugo, Pinus rotundata and Pinus uncinata, were sequenced and analyzed to gain new insight into their phylogenetic relationships. Comparative analysis of their complete chloroplast genome sequences revealed several mutational hotspots potentially useful for the genetic identification of taxa from the Pinus mugo complex. Phylogenetic inference based on sixteen complete chloroplast genomes of different coniferous representatives showed that pines from the Pinus mugo complex form one distinct monophyletic group. The results obtained in this study provide new and valuable omics data for further research within the European mountain pine complex. They also indicate which regions may be useful in the search for diagnostic DNA markers for the members of Pinus mugo complex and set the baseline in the conservation of genetic resources of its endangered taxa.

Seed Total Protein Profiling in Discrimination of Closely Related Pines: Evidence from the Pinus mugo Complex

The Pinus mugo complex includes several dozen closely related European mountain pines. The discrimination of specific taxa within this complex is still extremely challenging, although numerous methodologies have been used to solve this problem, including morphological and anatomical analyses, cytological studies, allozyme variability, and DNA barcoding, etc. In this study, we used the seed total protein (STP) patterns to search for taxonomically interesting differences among three closely-related pine taxa from the Pinus mugo complex and five more distant species from the Pinaceae family. It was postulated that STP profiling can serve as the backup methodology for modern taxonomic research, in which more sophisticated analyses, i.e., based on the DNA barcoding approach, have been found to be useless. A quantitative analysis of the STP profiles revealed characteristic electrophoretic patterns for all the analyzed taxa from Pinaceae. STP profiling enabled the discrimination of closely-related pine taxa, even of those previously indistinguishable by chloroplast DNA barcodes. The results obtained in this study indicate that STP profiling can be very useful for solving complex taxonomic puzzles.