BUZGO, MATYAS1*, DOUGLAS E. SOLTIS1, PAMELA S. SOLTIS2, BERNARD A. HAUSER1, and BO JOHANSEN3. 1Department of Botany, University of Florida, Bartram, P.O. Box 118526, Gainesville, FL 32611-8526, USA; 2Florida Natural History Museum, University of Florida, Dickinson Hall, P.O. Box 117800, Gainesville, FL 32611-7800, USA; 3Botanical Institute, Department of Evolutionary Botany, University of Copenhagen, Gothersgade 140, DK-1123 Copenhagen K, Denmark. - B-Class organ identity in basal monocots.
In basal monocots (e.g. Acoraceae, Alismatales s. APG 1998) it is
difficult to unravel the ancestral features of floral morphology by
comparison with their outgroups (magnoliids) and more derived clades
of monocots. Two general types occur: 1) flowers with distinct sepals
and petals, often two or several whorls of stamens and carpels, and
intercarpellary nectaries (e.g. Alismataceae, Butomaceae,
Hydrocharitaceae, Tofieldiaceae); 2) flowers with an undifferentiated
perianth consisting of tepals, one or two whorls of carpels, which are
often centrally fused and lack intercarpellary nectaries (e.g.
Acoraceae, Araceae, Aponogetonaceae, Juncaginaceae, Potamogetonaceae,
Scheuchzeriaceae). Type 1 is most similar to flowers in magnoliids
such as Annonaceae, Aristolochiaceae, and monocots such as
Dioscoreaceae and Liliaceae, whereas type 2 is similar to magnoliids
such as Saururaceae and Chloranthaceae. In current phylogenetic
analyses Acoraceae are sister to all other monocots, and
Aponogetonaceae are basal within Alismatales. Therefore, the second
type may represent a suite of morphologically plesiomorphic character
states. However, because these basal clades stand on long branches,
the actual features may as well have undergone extensive anagenesis,
and therefore represent autapomorphies.
To elucidate floral
evolution in these basal monocots, a better understanding of perianth
organ identity, differentiation and development is critical. Some of
the genes responsible for the differentiation of the perianth are
transcription factors of the MADS-box gene family, known as B-class
genes: orthologs of APETALA3 and PISTILLATA in
Arabidopsis, and DEFICIENS and GLOBULOSA in
Antirrhinum. Expression of B-class genes in perianth organs of
basal monocots exhibiting a morphologically undifferentiated perianth
would be consistent with a petaloid developmental program for these
organs, even though the perianth may appear bracteolar or sepalous in
later stages of development. B-class genes in the genus
Triglochin (Juncaginaceae) are characterized and the
application of reverse transcription in situ PCR (RT-ISPCR) is
discussed.
Key words: Flower Development, MADS-box genes, Monocots, Organ Identity, RT-ISPCR