Developmental and Structural Section
Frohlich, Mike , Brockington, Samuel F , Soltis, Pamela S. , Soltis, Douglas E. , Rudall, Paula J. .
Differing patterns of MADS-box gene expression associated with shifts in petaloidy within Aizoaceae (Caryophyllales).
An understanding of the genetic program controlling floral organ identity in model species has led to new approaches in the study of petal evolution. MADS-box genes may play an important role in generating floral diversity through changes in gene expression pattern. The family Aizoaceae provides an opportunity to test this hypothesis because, within this clade, different floral organ types serve as attractants for pollinators. In the early diverging subfamilies, Sesuvioideae and Aizooideae, the tepals of the uniseriate perianth are petaloid on the adaxial side, whereas in the later diverging subfamilies Mesembryanthoideae and Ruschoideae, the tepals are not petaloid and outer whorls of stamens are sterile and showy. In advance of gene expression analysis we characterised the floral development of a number of species of Aizoaceae. The development of the petaloid tepals of Sesuvioideae and Aizooideae is similar to that of a monocot foliage leaf such that the lamina is formed from the basal leaf sheath region. The petaloid tissue in these tepals appears to be homologous to the ephemeral tissue of the leaf sheath margin. Comparison of the epidermal and sub-epidermal features of the superficially similar petaloid tepals and petaloid staminodes revealed no shared morphological characteristics. Furthermore MADS-box gene expression appears to differ between the two petaloid organ types. In the petaloid staminodes of Mesembryanthoideae and Ruschoideae, PI and AP3 are both strongly expressed; however, in the petaloid tepals of Sesuvioideae and Aizooideae, PI expression is absent and AP3 is very weakly expressed. These differing patterns of gene expression may be explained if the petaloid tissue in the tepals is simply viewed as an expanded and pigmented margin of ephemeral leaf sheath tissue. The evolution of petaloid tissue through the expansion and pigmentation of the vegetative leaf sheath may have occurred without the co-involvement of PI and AP3.
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1 - Natural History Museum, Department of Botany, Cromwell Road, London, SW7 5BD, England
2 - University of Florida, Department of Botany, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
3 - University of Florida, Department of Botany, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida, 32611-8526, USA
4 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Molecular Systematics Section, Richmond, Surrey, TW9 3DS, United Kingdom
Presentation Type: Oral Paper:Papers for Sections
Location: Boulevard C/Hilton
Date: Tuesday, July 10th, 2007
Time: 10:15 AM