EVANS, RODGER C.1, LAWRENCE A. ALICE2*, CHRISTOPHER S. CAMPBELL3, TIMOTHY A. DICKINSON1, AND ELIZABETH A. KELLOGG4. 1Botany Department, University of Toronto, Toronto, Ontario, Canada M5S 3B2 and Centre for Biodiversity and Conservation Biology, Royal Ontario Museum, Toronto, Ontario, Canada M5S 2C6, 2Biology Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061, 3Department of Biological Sciences, University of Maine, Orono, ME 04469-5722, 4Harvard University Herbaria, Harvard University, Cambridge, MA., 02138. - Evidence for an allopolyploid origin of subfamily Maloideae s. l. (Rosaceae) from the nuclear granule-bound starch synthase (GBSS) or waxy gene.
We cloned and sequenced a 1.8—2.0 kb region near the 5’ end of the
GBSS gene of 13 Rosaceae genera: Rosa and Rubus
(subfamily Rosoideae); Exochorda, Oemleria, and
Prunus (Prunoideae s. l.), Aruncus and
Physocarpus (“Spiraeoideae”, which is clearly polyphyletic);
and Amelanchier, Chaenomeles, Kageneckia,
Malus, Osteomeles, and Vauquelinia (Maloideae s.
l.). This region includes two partial exons, seven complete exons
ranging in length from 64 bp to 244 bp, and seven or eight introns
ranging from 74 bp to 477 bp. Two highly divergent and
organizationally different types (A and B) of GBSS sequences
have been identified within individuals of five of the six sampled
genera of Maloideae s. l., but other Rosaceae individuals contain only
an A or B type. Type A GBSS maloid sequences have a large
first intron and no sixth intron, and type B maloid sequences plus
those of other Rosaceae have a short first intron and a sixth intron.
Parsimony analysis of Rosaceae GBSS exons with Pisum
(Fabaceae) as an outgroup yields a single most parsimonious tree with
separate, well supported clades of Rosoideae, Physocarpus, and
type A maloid sequences and Aruncus, Prunoideae s. l., and type
B maloid sequences. Thus, GBSS exons support the long
postulated allopolyploid origin of Maloideae s. l. GBSS is
consistent with nuclear ribosomal DNA internal transcribed spacers
(ITS) and chloroplast rbcL in supporting a broad
circumscription of Maloideae that includes the dry-fruited,
traditionally spiraeoid genera Kageneckia and
Vauquelinia. Within Amelanchier and Rubus, for
which we sequenced three species each, GBSS sequences show
slightly higher divergence than ITS sequences and the greater length
of GBSS promises increased phylogenetic signal within genera.
Key words: allopolyploidization, granule-bound starch synthase gene, Maloideae, Rosaceae