A Study On The Phylogenetics Of Fagales

The phylogenetic relationships of Fagales were investigated by means of molecular systematics, which was based on six DNA sequences from three genomes, including chloroplast DNA trnL-F, matK, rbcL, and atpB, nuclear 18S ribosomal DNA, and mitochondrial gene matR. Furthermore, nuclear PHYC gene was used to place Myricaceae with more confidence. In addition, the organogenesis of inflorescences and flowers of the monotypic genus Platycarya (Juglandaceae) was investigated with scanning electron microscopy (SEM). The results were summarized as follows:1 Four cpDNA trnL-F, matK, rbcL, and atpB sequences analysis The chloroplast trnL-F, matK, rbcL, and atpB sequences from 31 species representing nearly all genera of Fagales (sensu APG, 2003) were used to reconstruct the phylogeny of the order. Phylogenetic analyses based on individual data sets indicated that all of the families of Fagales are monophyletic, but some of the deepest branches are unresolved or only weakly supported. All phylogenetic trees based on these separate DNA sequences showed some degree of resolution, but topologies differ among the individual trees. No trees from two different sequences have exactly the same topology. The strict consensus tree of equally most parsimonious trees from each of these separate analyses is identical in some respects (e.g., recognized three major clades in Fagales and identifying Juglandaceae with Rhoipteleaceae as sister groups), differing mainly in the position of Myricaceae. For atpB, maximum parsimony analyses suggested that Myricaceae are sister to all other core "higher" hamamelids. The maximum parsimony trees (MPTs) of matK indicated that Myricaceae are sister to (Betulaceae-Ticodendraceae)-Casuarinaceae clade; however, trnL-F trees showed that Myricaceae are sister to Juglandaceae-Rhoiptelea clade. The combined analysis of the four cpDNA sequences showed similar topology to that in matK trees.2 Mitochondrial matR gene sequence analysisThe mitochondrial gene matR of 28 species representing 28 genera of Fagales, and 2 outgroups was sequenced. Based on this gene sequence 484 most parsimonious trees were generated. In the strict consensus tree of the 484 trees, the monophyly of Betulaceae and Fagaceae is strongly supported. Some unique relationships are identified with weak support, such as the sister relationships between Fagaceae and Rhoipteleaceae, as well as between Myricaceae and Casuarinaceae. The matR trees presented the lowest resolution among the trees based on the six separate DNA sequences used in our studies.3 18 S rDNA sequence analysis26 18S rDNA sequences from 26 genera of Fagales were analyzed. The monophyly of all families was supported in the strict consensus tree of 16 most parsimonious trees. The Fagales were divided into two groups, one including Fagaceae and Nothofagaceae, and the other including core "higher" hamamelids. The latter clade could be further divided into two strongly supported subclades: (Juglandaceae-Rhoipteleaceae)-Myricaceae, and (Betulaceae-Ticodendraceae)-Casuarinaceae.4 Six sequences combined analysesPhylogenetic reconstructions were performed under a number of scenarios for each of five combined data sets to elucidate the stability of the phylogeny trees. Inferred from the different combined analyses based on six DNA regions, the phylogenetic relationship within Fagales was discussed. The trees obtained in all of the combined analyses depict very similar family relationships (whether using maximum parsimony or Bayesian inference), with only a few differences in bootstrap support or Bayesian posterior probability for some clades. The topological differences observed between the MP and BI analyses focused on the internal clades of Juglandaceae and Fagaceae. All of the most parsimonious trees obtained based on the analyses of these combined data sets recognized three major clades in Fagales: (1)Nothofagus, (2) Fagaceae, and (3) core "higher" hamamelids represented by Casuarinaceae, Ticodendraceae, Betulaceae, Myricaceae, Juglandaceae, and Rhoipteleaceae. Except for the clade My...