EVANS, RODGER C.1* and CHRISTOPHER S. CAMPBELL2. 1Department of Biology, Acadia University, Wolfville, NS, B0P 1X0, CANADA; 2Department of Biological Sciences, University of Maine, Orono, ME, 04473-5751, USA. - Phylogenetic insights into the Maloideae (Rosaceae) from the granule-bound starch synthase I (GBSSI) gene.
The nuclear GBSSI gene is duplicated in all Rosaceae, and there is a
second duplication in all members of subfamily Maloideae, including
three genera with dry fruits that have not traditionally been included
in the subfamily, Kageneckia, Lindleya, and
Vauquelinia. We obtained sequence for about 1800 nucleotide
sites, including seven complete exons and eight introns (only seven in
two of the four copies of the gene) plus parts of the first and ninth
exons at the 5' end of the gene. In a sample that includes all but two
of the 32 genera in the family, we have sequences for all four copies
of the gene for 14 genera, for three copies for 6 genera, for two
copies for 9 genera, and for just one copy for Pseudocydonia.
That we are readily able to align introns within each copy of the gene
is compatible with the low sequence divergence in this gene (about 2
to 5% between Maloideae genera other than Kageneckia,
Lindleya, and Vauquelinia) and in other molecular data.
Analysis of GBSSI sequence data for our sample plus the sister group
of Maloideae (Porteranthus) supports a sister-group
relationship between Kageneckia, Lindleya, plus
Vauquelinia and the remainder (core) of the Maloideae. We
therefore use these three genera as outgroups for analyses of core
Maloideae. The data give strong support for monophyly of core
Maloideae and varying levels of support for several groups of two to
three genera, namely Amelanchier, Malacomeles, plus
Peraphyllum; Aria plus Chamaemespilus;
Cotoneaster plus Malus; and Dichotomanthes plus
Photinia. Short branch lengths characterize much of the most
parsimonious trees, suggesting rapid diversification and frustrating
our efforts to understand higher-level relationships in the
subfamily.
Key words: exons, gene duplication, introns, Maloideae, Rosaceae, sequence divergence