Study On Phylogenetic Relationships Of Syringa In Northeast China Based On NrDNAITS Regions

It's significant using genes or sequences with fitful evolutional ratio to infer the phylogenetic relationships in molecular phylogenetics. Sequences of the internal transcribed spacer (ITS) of nuclear ribosomal DNA, which can provide abundant phylogenetically informative sites with fast evolutionary ratio, have been proven to be of great significance in phylogenetic and evolutionary studies of many angiosperm taxa at specific, sectional and generic levels. The infrageneric relationships in Syringa are not consentaneous in different studies, especially the basal clade in the infrageneric groups and the phylogenetic position of Subgenus Ligustrina, Therefore, it is necessary to explore the phylogenetic relationships in Syringa with different methods.The internal transcribed spacer (ITS) regions of nuclear ribosomal DNA (including 5.8S rRNA) of 11 Syringa species, representing major species of the genus in Northeast China, were sequenced, and 1 outgroup was sequenced for the rooting purpose. Together with the ITS sequences downloaded from GenBank, the species, Series and Subgenus phylogenetic relationships in this genus were explored by employing MEGA2.1 software. The results are as follows.1.The nrDNA ITS sequences of the 11 species in Syringa from Northeast China and one outgroup were obtained by primer designing, PCR, cloning and sequencing, which subsequently were used to analyze the phylogenetic relationships in the genus by homologous blast and clade analysis.2. In the data set of 11 species from Northeast China, the percentage of phylogenetically informative sites is 6.3% in ITS regions (including two spacers, without 5.8S subunit). In the data set including the ITS sequences downloaded from GenBank, the percentage of phylogenetically informative sites is 12.2%. According to the above statistics, there are relatively abundant informative sites in the ITS sequences of genus Syringa. The phylogenetic analyses based on the ITS sequences are in consensus with the morphological classification of the groups within the genus to a degree, which proved that the ITS regions are valuable to resolve the phylogenetic relationships in Syringa.3. In the infrageneric classification of Syringa based on morphologic characters, Subgenus Ligustrina, characterized by short corolla tubes and long exserted stamens, is sister to the remaining Series in Subgenus Syringa. Whereas, in the phylogenetic anslyses based on ITS sequences, Subgenus Ligustrina is not the most basal taxon, i.e. Subgenus Ligustrina is not sister to the rest of the genus. Alternatively, Subgenus Ligustringa is phylogenetically embedded within the Subgenus Syringa clade in all the three ITS-based trees employing UPGMA, NJ and MP analyses. It is suggested that Subgenus Ligustringa is probably derived from within Subgenus Syringa, maybe it is not the primarily diverged group in Syringa.4.1n the ITS-based trees of 11 species in Syringa from Northeast China, Series Syringa, Series Pubescentes, Series VUlosae and Subgenus Ligustrina form their own clades with well bootstrap support(bootstrap>90%). However, in the ITS-based tree from the data set including the sequences from the GenBank, Series Villosae is not a well-supported monophyletic group, while the rest Series and Subgenus Ligustrina form their own well-supported monphyletic groups.5.Series Villosae is the well-supported basal taxon in the phylogenetic analyses of 11 species from Northeast China. However, this phylogenetic relationship is weakly supported in the comprehensive phylogenetic analysis based on the data set of 50 sequences from 22 species in Syringa. Even though, it is inferred that Series Villosae is probably the primarily diverged group in Syringa.6. Phylogenetic analyses based on ITS sequences infer the following phylogenetic relationships of the infrageneric clades in Syringa: Series Villosae is basal to the rest of the genus; Series Pinnatifoliae is sister to Series Syringa and Series Pinnatifoliae is sister to Series Syringa, these two clades are sister to each other. The relationship between Series Syringa and Series Pinnatifoliae is strongly supported, and the bootstrap among the rest clades are over than 50%.