title: Partial redundancy and functional specialization of E-class SEPALLATA genes in an early-diverging eudicot.
abstract: Plant MADS-box genes have duplicated extensively, allegedly contributing to the immense diversity of floral form in angiosperms. In Arabidopsis thaliana (a core eudicot model plant), four SEPALLATA (SEP) genes comprise the E-class from the extended ABCE model of flower development. They are redundantly involved in the development of the four types of floral organs (sepals, petals, stamens and carpels) and in floral meristem determinacy. E-class genes have been examined in other core eudicots and monocots, but have been less investigated in non-core eudicots. Our goal was to functionally characterize the E-class genes in the early-diverging eudicot Thalictrum thalictroides (Ranunculaceae), whose flowers are apetalous. We identified four SEP orthologs, which when placed in a phylogenetic context, resulted from a major gene duplication event before the origin of angiosperms and a subsequent duplication at the origin of the Ranunculales. We used Virus-Induced Gene Silencing (VIGS) to down-regulate the three expressed paralogs individually and in combination to investigate their function and to determine the degree of conservation versus divergence of this important plant transcription factor. All loci were partially redundant in sepal and stamen identity and in promoting petaloidy of sepals, yet the SEP3 ortholog had a more pronounced role in carpel identity and development. The two other paralogs appear to have subfunctionalized in their cadastral roles to keep the boundaries between either sepal and stamen zones or stamen and carpel zones. Double knockdowns had enhanced phenotypes and the triple knockdown had an even more severe phenotype that included partial to complete homeotic conversion of stamens and carpels to sepaloid organs and green sepals, highlighting a role of E-class genes in petaloidy of sepals in this species. While no floral meristem determinacy defects were observed, this could be due to residual amounts of gene expression in the VIGS experiments being sufficient to perform this function or to the masking role of a redundant gene.
authors: Department of Biology, University of Washington, Seattle, WA 98195, United States.
authors: Valerie L
authors: VL
authors: Soza
authors: Department of Biology, University of Washington, Seattle, WA 98195, United States.
authors: Corey D
authors: CD
authors: Snelson
authors: Department of Biology, University of Washington, Seattle, WA 98195, United States.
authors: Kristen D
authors: KD
authors: Hewett Hazelton
authors: Department of Biology, University of Washington, Seattle, WA 98195, United States. Electronic address: distilio@uw.edu.
authors: Verónica S
authors: VS
authors: Di Stilio
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology; D018744:DNA, Plant / Q000235:genetics; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D017343:Genes, Plant; D056726:Genetic Association Studies; D018519:Meristem / Q000166:cytology; D008954:Models, Biological; D005810:Multigene Family / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000502:physiology; D030821:Plants, Genetically Modified; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D031949:Thalictrum / Q000235:genetics* / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D010940:Plant Proteins; C587509:SEPALLATA protein, Arabidopsis; D014157:Transcription Factors
keywords: ABC model; Evo-devo; Flower development; MADS-box genes; Non-core eudicot; Ranunculid; SEPALLATA; Thalictrum; Virus-Induced Gene Silencing