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MBE Advance Access published online on April 3, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn001
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Article

Positive selection and expression divergence following gene duplication in the sunflower CYCLOIDEA gene family

MA Chapman*, JH Leebens-Mack and JM Burke

Department of Plant Biology, Miller Plant Sciences Building, University of Georgia, Athens, GA 30602

* Corresponding author email mchapman{at}plantbio.uga.edu, phone 706-583-5510, fax 706-583-1805

Received for publication August 8, 2007. Revision received October 31, 2007. Accepted for publication December 28, 2007.

Members of the CYCLOIDEA (CYC)/ TEOSINTE-BRANCHED1 (TB1) group of transcription factors have been implicated in the evolution of zygomorphic (i.e., bilaterally-symmetric) flowers in Antirrhinum and Lotus and the loss of branching phenotype during the domestication of maize. The composite inflorescences of sunflower (Helianthus annuus L. Asteraceae) contain both zygomorphic and actinomorphic (i.e., radially-symmetric) florets (rays and disks, respectively), and the cultivated sunflower has evolved an unbranched phenotype in response to domestication from its highly branched wild progenitor; hence, genes related to CYC/TB1 are of great interest in this study system. We identified ten members of the CYC/TB1 gene family in sunflower, which is more than found in any other species investigated to date. Phylogenetic analysis indicates that these genes occur in three distinct clades, consistent with previous research in other eudicot species. A combination of dating the duplication events and linkage mapping indicates that only some of the duplications were associated with polyploidization. Cosegregation between CYC-like genes and branching-related QTL suggest a minor, if any, role for these genes in conferring differences in branching. However, the expression patterns of one gene suggest a possible role in the development of ray versus disk florets. Molecular evolutionary analyses reveal that residues in the TCP and R domains were the targets of positive selection following gene duplication. Taken together, these results indicate that gene duplication and functional divergence have played a major role in diversification of the sunflower CYCLOIDEA gene family.

Key Words: CYCLOIDEA • floral development • Helianthus • sunflower • TEOSINTE-BRANCHED1 • transcription factors


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