title: Conserved differential expression of paralogous DEFICIENS- and GLOBOSA-like MADS-box genes in the flowers of Orchidaceae: refining the 'orchid code'.
abstract: In flowering plants, class-B floral homeotic genes encode MADS-domain transcription factors, which are key in the specification of petal and stamen identity, and have two ancient clades: DEF-like and GLO-like genes. Many species have one gene of each clade, but orchids have typically four DEF-like genes, representing ancient gene clades 1, 2, 3 and 4. We tested the 'orchid code', a combinatorial genetic model suggesting that differences between the organs of the orchid perianth (outer tepals, inner lateral tepals and labellum) are generated by the combinatorial differential expression of four DEF-like genes. Our experimental test involves highly sensitive and specific measurements, with qRT-PCR of the expression of DEF- and GLO-like genes from the distantly related Vanilla planifolia and Phragmipedium longifolium, as well as from wild-type and peloric Phalaenopsis hybrid flowers. Our findings support the first 'orchid code' hypothesis, in that absence of clade-3 and -4 gene expression distinguishes the outer tepals from the inner tepals. In contrast to the original hypothesis, however, mRNA of both clade-3 and -4 genes accumulates in wild-type inner lateral tepals and the labellum, and in labellum-like inner lateral tepals of peloric flowers, albeit in different quantities. Our data suggest a revised hypothesis where high levels of clade-1 and -2, and low levels of clade-3 and -4, gene expression specify inner lateral tepals, whereas labellum development requires low levels of clade-1 and -2 expression and high levels of clade-3 and -4 expression.
authors: Department of Genetics, Friedrich Schiller University Jena, Philosophenweg 12, 07743 Jena, Germany. mariana.mondragon@biologie.uni-regensburg.de
authors: Mariana
authors: M
authors: Mondragón-Palomino
authors: Günter
authors: G
authors: Theissen
mesh_terms: D000595:Amino Acid Sequence; D019143:Evolution, Molecular; D035264:Flowers / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D005801:Genes, Homeobox; D017343:Genes, Plant; D026161:MADS Domain Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D029595:Orchidaceae / Q000235:genetics* / Q000254:growth & development; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000032:analysis; D012680:Sensitivity and Specificity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D026161:MADS Domain Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D014157:Transcription Factors