Conserved differential expression of paralogous DEFICIENS‐ and GLOBOSA‐like MADS‐box genes in the flowers of Orchidaceae: refining the ‘orchid code’

Abstract

SUMMARYIn 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.

The Maize PI/GLO Ortholog Zmm16/sterile tassel silky ear1 Interacts with the Zygomorphy and Sex Determination Pathways in Flower Development

“…Functional studies of the CYC-like genes in the grasses implicate them in the control of shoot branching (Doebley et al, 1995;Kebrom et al, 2006), inflorescence branch angle and leaf morphology (Bai et al, 2012), and lemma versus palea identity in rice (Yuan et al, 2009), not structural floral zygomorphy. In a number of orchids, the development of distinct second and third whorl tepals associated with zygomorphy is associated with variability in AP3/DEF homolog expression and variability in floral MADS box complex formation (Mondragón-Palomino and Theissen, 2008Theissen, , 2011Hsu et al, 2015). Aside from these sparse examples, the genetic underpinnings of floral zygomorphy in the broader monocots remain largely mysterious.…”

Developmental and evolutionary diversity of plant MADS-domain factors: insights from recent studies

“…B-class gene duplications followed by functional divergence have also been implicated in the formation of different tepal types in orchids (e.g. Chang et al, 2010;Mondragón-Palomino and Theissen, 2011). However, the evolution of petal-like sepals may not always involve shifts in B-class gene expression (Landis et al, 2012).…”

Molecular Mechanism Regulating Floral Architecture in Monocotyledonous Ornamental Plants

“…Phylogenetic analyses showed that orchid GLO-like genes form a single clade, which is duplicated once in the subfamily Orchidaceae , and these genes are expressed in all floral organs Mondragón-Palomino and Theißen, 2011;Pan et al, 2011;Tsai et al, 2005). By contrast, orchid has four well-supported lineages of DEF-like genes, which belong to Clade 1 to Clade 4 ( …”