ALICE, LAWRENCE A.* and AMBER HOGART. Department of Biology, Biotechnology Center, and Center for Biodiversity Studies, Western Kentucky University, Bowling Green KY 42101. - Phylogeny of Rubus (Rosaceae) based on Granule-Bound Starch Synthase I (GBSSI) gene sequences.
The need for biparentally inherited, nuclear DNA markers useful at
lower taxonomic levels in plant systematics research has revealed
several exciting possibilities. One includes the granule-bound starch
synthase I (GBSSI) gene comprising 13 translated exons and 12 introns
in most species examined. Rubus (Rosaceae) typifies a group
where GBSSI sequences may yield valuable information. Sequences of the
nrDNA ITS region and, more recently, of three chloroplast DNA regions
initially provided insight into the systematics of Rubus.
However, none offers sufficient numbers of phylogenetically
informative characters to generate robust hypotheses of relationship.
Thus, we sequenced the 5' end of the GBSSI gene for five Rubus
species representing three clades. GBSSI in Rubus and
Rosa (both Rosoideae) occurs at two paralogous loci; GBSSI-1
and GBSSI-2. The region we sequenced includes seven complete exons,
two partial exons, and eight introns. Total number of aligned
nucleotides is 2157 using Rosa as an outgroup, with exons and
introns ranging in length from 64 to 244 bp and from 64 to 477 bp,
respectively. Analysis of exons and introns or introns alone recovers
a single most parsimonious tree which is consistent with both ITS and
chloroplast phylogenies generated previously. Although pairwise
divergences for distantly related species are slightly lower for
GBSSI-1 introns than for ITS 1 + ITS 2, they are notably higher for
closely related species; divergence between R. cuneifolius and
R. hispidus is 0.4% for ITS but 2.1% for GBSSI-1. Percent
parsimony-informative characters is also higher in GBSSI-1 (6.0%) than
in ITS (2.0%). Given that aligned sequences of GBSSI-1 introns are
nearly 2.5-fold longer than ITS 1 + ITS 2 (1216 bp vs. 493 bp,
respectively) and show higher levels of divergence, we believe the 5'
region of GBSSI-1 holds great promise for phylogeny reconstruction of
Rubus and potentially other plant groups, especially at lower
Key words: GBSSI, phylogeny, Rosaceae, Rubus, systematics