Developmental and Structural Section
Livshultz, Tatyana , Kramer, Elena M .
Expression patterns of A- and C-class MADS-box genes identify the corona of Asclepias syriaca (Apocynaceae) as staminal appendages.
Coronas are prominent structures in the flowers of most species of subfamilies Asclepiadoideae and Secamonoideae (milkweeds sensu lato, family Apocynaceae) that perform a variety of functions including pollinator attraction, reward, and positioning to trigger the pollen transfer mechanism. Coronas develop late in floral ontogeny, long after the four standard organ whorls (sepals, petals, stamens, carpels) are well differentiated, indicating that corona appendages are not homeotic transformations of any of the standard floral organs. The positional homology of coronas of milkweeds sensu lato with those of other Apocynaceae has been controversial. One hypothesis proposes that the most frequently encountered corona type of Asclepiadoideae and Secamonoideae consists of staminal appendages while the most frequently encountered corona type of other Apocynaceae is corolline appendages. An alternative hypothesis proposes that coronas of milkweeds and other Apocynaceae are all corolline appendages. To test these two alternative hypotheses, we have cloned A- and C-class MADS-box genes from Asclepias syriaca and used RT-PCR to detect their expression in sepals, petals, corona lobes, and the fused anthers and pistil (gynostegium pro parte) of late-stage buds. One ortholog each of AP1 (A-class) and PLENA and AGAMOUS (C-class) were cloned. The AP1 ortholog is expressed in sepals and petals but not in coronas or anthers and pistil. The PLENA and AGAMOUS orthologs are expressed in coronas and anthers and pistil but not in sepals and petals. These gene expression patterns identify the corona of Asclepias syriaca as appendages of the stamen.
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1 - Academy of Natural Sciences of Philadelphia, Botany Department, 1900 Benjamin Franklin Parkway, Philadelphia, PA, 19103-1101, USA
2 - Harvard University, Organismic and Evolutionary Biology, 16 Divinity Ave, Biolabs 1109
, Cambridge, MA, 02138, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Maybird/Cliff Lodge - Level C
Date: Tuesday, July 28th, 2009
Time: 2:00 PM