BUNSAWAT, JIRANAN* and LAWRENCE A. ALICE. Department of Biology, Biotechnology Center, and Center for Biodiversity Studies, Western Kentucky University, Bowling Green KY 42101. - Molecular Characterization and Phylogenetic Utility of nrDNA ETS Sequences in Rubus (Rosaceae).
In a continuing effort to gain insight into the systematics of
Rubus (Rosaceae), we examined the external transcribed spacer
(ETS) of nuclear ribosomal DNA (nrDNA) to assess its suitability for
phylogenetic analysis. We sampled four Rubus species (R.
arcticus, R. idaeus, R. odoratus, and R.
trivialis) representing four subgenera and corresponding to
distinct clades based on previous analysis of ITS region sequences. We
PCR amplified the entire nrDNA intergenic spacer (IGS) using universal
primers (18S-IGS and 26S-IGS). The size of IGS in Rubus is
approximately 2.5 kb. We sequenced the 3' end of ETS using primer
18S-E. ETS sequences of these species can be readily aligned by eye.
Pairwise divergences among the four species noted from the ETS data
range from 4.0 to 5.9% with a mean of 4.5%, whereas data from the ITS
region for these same species range from 4.4 to 9.3% with a mean of
6.8%. Percent variable/parsimony-informative sites for ETS and ITS 1 +
ITS 2 are 10.2/0.7% and 12.8/1.0% respectively. In contrast to
published studies of ETS sequences in other plant taxa, variation in
ETS is somewhat lower than for ITS in these four Rubus species.
However, we have only sequenced the 3' portion of ETS, which is
expected to be conserved.
Key words: ETS, nrDNA, phylogeny, Rosaceae, Rubus