title: Evolution of class B floral homeotic proteins: obligate heterodimerization originated from homodimerization.
abstract: The class B floral homeotic genes from the higher eudicot model systems Arabidopsis and Antirrhinum are involved in specifying the identity of petals and stamens during flower development. These genes exist in two different types termed DEF- and GLO-like genes. The proteins encoded by the class B genes are stable and functional in the cell only as heterodimeric complexes of a DEF- and a GLO-like protein. In line with this, heterodimerization is obligate for DNA binding in vitro. The genes whose products have to heterodimerize to be stable and functional are each other's closest relatives within their genomes. This suggests that the respective genes originated by gene duplication, and that heterodimerization is of relative recent origin and evolved from homodimerization. To test this hypothesis we have investigated the dimerization behavior of putative B proteins from phylogenetic informative taxa, employing electrophoretic mobility shift assays and the yeast two-hybrid system. We find that an ancestral B protein from the gymnosperm Gnetum gnemon binds DNA in a sequence-specific manner as a homodimer. Of the two types of B proteins from the monocot Lilium regale, the GLO-like protein is still able to homodimerize, whereas the DEF-like protein binds to DNA only as a heterodimeric complex with the GLO-like protein. These data suggest that heterodimerization evolved in two steps after a gene duplication that gave rise to DEF- and GLO-like genes. Heterodimerization may have originated after the gymnosperm-angiosperm split about 300 MYA but before the monocot-eudicot split 140-200 MYA. Heterodimerization may have become obligate for both types of flowering plant B proteins in the eudicot lineage after the monocot-eudicot split.
authors.affiliation: Max-Planck-Institut für Züchtungsforschung, Abteilung Molekulare Pflanzengenetik, Carl-von-Linné-Weg 10, D-50829 Köln, Germany.
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Winter
authors.forename: Christof
authors.initials: C
authors.lastname: Weiser
authors.forename: Kerstin
authors.initials: K
authors.lastname: Kaufmann
authors.forename: Arend
authors.initials: A
authors.lastname: Bohne
authors.forename: Charlotte
authors.initials: C
authors.lastname: Kirchner
authors.forename: Akira
authors.initials: A
authors.lastname: Kanno
authors.forename: Heinz
authors.initials: H
authors.lastname: Saedler
authors.forename: Günter
authors.initials: G
authors.lastname: Theissen
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D032462:Cycadopsida / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D019281:Dimerization; D019143:Evolution, Molecular; D005801:Genes, Homeobox; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D027762:Lilium / Q000235:genetics; D019684:Magnoliopsida / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D010944:Plants / Q000145:classification* / Q000235:genetics*; D020798:Two-Hybrid System Techniques
chemical_list: D018744:DNA, Plant; D018398:Homeodomain Proteins; D010940:Plant Proteins