Wenheng Zhang, Elena M. Kramer, and Charles C. Davis1
-Author Affiliations
Department of Organismic and Evolutionary Biology, Harvard University Herbaria, Cambridge, MA 02138
Edited by Michael J. Donoghue, Yale University, New Haven, CT, and approved February 10, 2010 (received for review September 8, 2009)
Abstract
The evolution of floral zygomorphy is an important innovation in flowering plants and is thought to arise principally from specialization on various insect pollinators. Floral morphology of neotropical Malpighiaceae is distinctive and highly conserved, especially with regard to symmetry, and is thought to be caused by selection by its oil-bee pollinators. We sought to characterize the genetic basis of floral zygomorphy in Malpighiaceae by investigatingCYCLOIDEA2-like (CYC2-like) genes, which are required for establishing symmetry in diverse core eudicots. We identified two copies of CYC2-like genes in Malpighiaceae, which resulted from a gene duplication in the common ancestor of the family. A likely role for these loci in the development of floral zygomorphy in Malpighiaceae is demonstrated by the conserved pattern of dorsal gene expression in two distantly related neotropical species, Byrsonima crassifolia andJanusia guaranitica. Further evidence for this function is observed in a Malpighiaceae species that has moved to the paleotropics and experienced coincident shifts in pollinators, floral symmetry, and CYC2-like gene expression. The dorsal expression pat-tern observed in Malpighiaceae contrasts dramatically with their actinomorphic-flowered relatives, Centroplacaceae (Bhesa paniculata)and Elatinaceae (Bergia texana). In particular, B. texana exhibits a previously undescribed pattern of uniform CYC2 expression, suggesting that CYC2expression among the actinomorphic ancestors of zygomorphic lineages may be much more complex than previously thought. We consider three evolutionary models that may have given rise to this patterning, including the hypothesis that floral zygomorphy in Malpighiaceae arose earlier than standard morphology-based character reconstructions suggest.
CYCLOIDEA development gene duplication Malpighiaceae phylogeny
Footnotes
1To whom correspondence should be addressed. E-mail:cdavis@oeb.harvard.edu.
Author contributions: W.Z., E.M.K., and C.C.D. designed research; W.Z. performed research; W.Z., E.M.K., and C.C.D. analyzed data; and W.Z., E.M.K., and C.C.D. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. GU982187–GU982264).
This article contains supporting information online at www.pnas.org/cgi/content/full/0910155107/DCSupplemental.
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