Originally published as Genetics Published Articles Ahead of Print on January 31, 2005.

Genetics, Vol. 169, 2209-2223, April 2005, Copyright © 2005
doi:10.1534/genetics.104.037770

The Evolution of the SEPALLATA Subfamily of MADS-Box Genes

A Preangiosperm Origin With Multiple Duplications Throughout Angiosperm History

Laura M. Zahn^*,1, Hongzhi Kong^*,,1, James H. Leebens-Mack^*, Sangtae Kim, Pamela S. Soltis, Lena L. Landherr^*, Douglas E. Soltis, Claude W. dePamphilis^* and Hong Ma^*,2

^* Department of Biology, Huck Institutes of the Life Sciences and Institute for Molecular Genetics and Evolution, The Pennsylvania State University, University Park, Pennsylvania 16802
Laboratory of Systematic and Evolutionary Botany, Institute of Botany, The Chinese Academy of Sciences, Xiangshan, Beijing 100093, People's Republic of China
Department of Botany and Genetics Institute, University of Florida, Gainesville, Florida 32611
Florida Museum of Natural History and Genetics Institute, University of Florida, Gainesville, Florida 32611

² Corresponding author: Department of Biology, Life Sciences Bldg., 315 Wartik Lab, Pennsylvania State University, University Park, PA 16802.
E-mail: hxm16{at}psu.edu

Members of the SEPALLATA (SEP) MADS-box subfamily are required for specifying the "floral state" by contributing to floral organ and meristem identity. SEP genes have not been detected in gymnosperms and seem to have originated since the lineage leading to extant angiosperms diverged from extant gymnosperms. Therefore, both functional and evolutionary studies suggest that SEP genes may have been critical for the origin of the flower. To gain insights into the evolution of SEP genes, we isolated nine genes from plants that occupy phylogenetically important positions. Phylogenetic analyses of SEP sequences show that several gene duplications occurred during the evolution of this subfamily, providing potential opportunities for functional divergence. The first duplication occurred prior to the origin of the extant angiosperms, resulting in the AGL2/3/4 and AGL9 clades. Subsequent duplications occurred within these clades in the eudicots and monocots. The timing of the first SEP duplication approximately coincides with duplications in the DEFICIENS/GLOBOSA and AGAMOUS MADS-box subfamilies, which may have resulted from either a proposed genome-wide duplication in the ancestor of extant angiosperms or multiple independent duplication events. Regardless of the mechanism of gene duplication, these pairs of duplicate transcription factors provided new possibilities of genetic interactions that may have been important in the origin of the flower.

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