Phylogenetic relationships within Cornus (Cornaceae) based on 26S rDNA sequences.

Area of Science:

• Botany
• Molecular Biology
• Phylogenetics

Background:

• Phylogenetic relationships within the dogwood genus Cornus are complex and have been historically controversial.
• Previous studies using chloroplast DNA (cpDNA) and morphological data yielded incongruent phylogenetic hypotheses for Cornus.

Purpose of the Study:

• To resolve phylogenetic ambiguities in the dogwood genus Cornus.
• To test existing phylogenetic hypotheses using nuclear 26S ribosomal DNA (rDNA) sequence data.
• To evaluate the utility of 26S rDNA sequences for phylogenetic analysis below the genus level.

Main Methods:

• Sequencing of the nuclear 26S rDNA gene from 16 species (13 Cornus, 3 outgroups).
• Phylogenetic analyses using parsimony and maximum likelihood methods on aligned sequences (3380 bp).
• Combined analysis of 26S rDNA and existing cpDNA data.

Main Results:

• Phylogenetic trees derived from 26S rDNA data are consistent with cpDNA-based inferences.
• Specific clades identified include dwarf dogwoods, big-bracted dogwoods, cornelian cherries, and blue/white-fruited dogwoods.
• Combined 26S rDNA and cpDNA analyses provided stronger support for the inferred phylogenetic relationships.

Conclusions:

• Nuclear 26S rDNA sequences are valuable for resolving phylogenetic relationships within the Cornus genus.
• The study provides a robust phylogenetic framework for Cornus, reconciling previous conflicting data.
• Expansion segments within 26S rDNA evolve rapidly, enhancing their phylogenetic utility.