An apparent reversal in floral symmetry in the legume Cadia is a homeotic transformation

doi:10.1073/pnas.0600986103

An apparent reversal in floral symmetry in the legume Cadia is a homeotic transformation

*Royal Botanic Garden Edinburgh, 20a Inverleith Row, Edinburgh EH3 5LR, United Kingdom;
^†Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3JR, United Kingdom; and
^§University of British Columbia Botanical Garden, Room 206, Campbell Building, 6804 Southwest Marine Drive, Vancouver, BC, Canada V6T 1Z4

Edited by Michael J. Donoghue, Yale University, New Haven, CT, and approved June 26, 2006 (received for review February 8, 2006)

Abstract

Within papilionoid legumes, characterized by flowers with strong bilateral symmetry, a derived condition within angiosperms, Cadia (Cadia purpurea) has reverted to radially symmetrical flowers. Here, we investigate the genetic basis of this morphological reversal. Two orthologues of the floral symmetry gene CYCLOIDEA (CYC) demarcate the adaxial (dorsal) region of the flower in typical papilionoid legumes. In the model legume Lotus japonicus, one of these LegCYC genes has been shown, like CYC, to be required for the establishment of floral bilateral symmetry. This study shows that these genes are expressed in the adaxial region of the typical papilionoid flower of Lupinus, which belongs to the same papilionoid subclade as Cadia. In Cadia, these genes also are expressed, but the expression pattern of one of these has expanded from the adaxial to the lateral and abaxial regions of the corolla. This result suggests that the radial flowers of Cadia are dorsalized and, therefore, are not a true evolutionary reversal but an innovative homeotic transformation, where, in this case, all petals have acquired dorsal identity. This study raises a question over other putative reversals in animals and plants, which also may be cryptic innovations.

Footnotes

^‡To whom correspondence should be addressed. E-mail: h_citerne{at}hotmail.com
Author contributions: H.L.C., R.T.P., and Q.C.B.C. designed research; H.L.C. performed research; H.L.C. analyzed data; and H.L.C., R.T.P., and Q.C.B.C. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Data deposition: The sequences reported in the paper for Lupinus nanus LEGCYC1A and LEGCYC1B and Cadia purpurea LEGCYC1A and LEGCYC1B have been deposited in the GenBank database (accession nos. AY382156, AY382155, AY225826, and AY225825).