Colloquium: Assembling the Tree of Life Colloquium
Zhang, Wenheng , Kramer, Elena M , Davis, III, Charles C. .
CYCLOIDEA2 and the origin and maintenance of floral zygomorphy in Malpighiaceae.
Phylogenetic relationships in Malpighiales are being resolved at a rapid pace, thus allowing us to begin elucidating the origin of morphological features within this diverse clade. Floral zygomorphy is an important innovation in flowering plants and is generally thought to have resulted from selection by specialized insect pollinators. We sought to characterize the genetic basis of floral zygomorphy in Malpighiaceae by investigating the CYCLOIDEA2-like (CYC2-like) genes, which are required for establishing symmetry in diverse phylogenetic lineages. Floral morphology of the neotropical members of this clade is distinctive and highly conserved, especially with regard to symmetry, and is thought to be due to selection by oil-bee pollinators. We identified two forms of CYC2-like genes in Malpighiaceae, CYC2A and CYC2B, which resulted from a gene duplication in the common ancestor of the family. A potential role for these loci in the development of floral zygomorphy in the Malpighiaceae is exemplified by the conserved pattern of gene expression in two distantly related neotropical species, Byrsonima crassifolia and Janusia guaranitica. Both CYC2A and CYC2B are expressed only in the dorsal region of the flowers in these species. Further evidence for this function derives from expression patterns in a species that has moved to the paleotropics, where the oil bee pollinators are absent, and has lost its stereotyped morphology. In Tristellateia australasiae, CYC2A expression mirrors a shift in the plane of floral symmetry, while CYC2B has been lost. The conserved pattern in Malpighiaceae contrasts dramatically with their recently identified radially flowered relatives, Centroplaceae and Elatinaceae. We hypothesize that the anomalous radial pattern in Elatinaceae (versus no late stage expression in Centroplaceae) arose secondarily from a zygomorphic flowered ancestor shared with Malpighiaceae, as has been recently demonstrated for radial flowered members of the zygomorphic clade Fabaceae.
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1 - Harvard University, Department of Organismal and Evoloutionary Biology, 22 Divinity Ave., Cambridge, MA, 02138
2 - Harvard Univerisity, Organismic and Evolutionary Biology, 16 Divinity Ave, Biolabs 1109, Cambridge, Massachusetts, 02138, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Cottonwood C/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 3:15 PM