Characterization of the Antirrhinum floral homeotic MADS-box gene deficiens: evidence for DNA binding and autoregulation of its persistent expression throughout flower development.

Abstract

We have determined the structure of the floral homeotic deficiens (defA) gene whose mutants display sepaloid petals and carpelloid stamens, and have analysed its spatial and temporal expression pattern. In addition, several mutant alleles (morphoalleles) were studied. The results of these analyses define three functional domains of the DEF A protein and identify in the deficiens promoter a possible cis‐acting binding site for a transcription factor which specifically upregulates expression of deficiens in petals and stamens. In vitro DNA binding studies show that DEF A binds to specific DNA motifs as a heterodimer, together with the protein product of the floral homeotic globosa gene, thus demonstrating that the protein encoded by deficiens is a DNA binding protein. Furthermore, Northern analysis of a temperature sensitive allele at permissive and non‐permissive temperatures provides evidence for autoregulation of the persistent expression of deficiens throughout flower development. A possible mechanism of autoregulation is discussed.

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

“…Class-B floral organ identity genes, encoding MADS-domain transcription factors, have a central role in the specification of petal and stamen identity (Sommer et al, 1990;Jack et al, 1992Jack et al, , 1994Schwarz-Sommer et al, 1992;Trobner et al, 1992;Goto and Meyerowitz, 1994;Krizek and Meyerowitz, 1996). DEF-and GLO-like genes, the two major lineages of class-B genes in angiosperms, originated from a gene duplication event that preceded the origin of extant angiosperms (Kramer et al, 1998).…”

Control of Pigment Biosynthesis Genes during Petal Development.

“…It is therefore possible that the homeotic genes that determine floral whorl identity may also play a subsequent role in tissue-specific gene expression because their expression continues late into organ morphogenesis. If this is the case, genes such as deficiens (Def) and globosa (Glo) in Antirrhinum and green petals in petunia might be directly involved in the activation of pigment biosynthetic genes (Sommer et al, 1990;Angenent et al, 1992;Schwarz-Sommer et al, 1992). Although the discovery of specialized regulators such as De/ argues against such a direct role for homeotic genes, there is some evidence from analysis of revertant somatic sectors of Def, seen as small islands of petal cells in sepal tissue, to suggest that Def remains functionally active late into organ development and may induce pigmented petal cell formation late in organ differentiation .…”

The MADS-domain protein PPM2 preferentially occurs in gametangia and sporophytes of the moss Physcomitrella patens

“…The C-terminal domain is the major structural determinant for the formation of higher order protein complexes and sometimes possesses transcriptional activation domains. To fulfil their regulatory functions, MIKC c MADS-domain proteins bind as obligate protein-dimers to so-called CArG-box recognition sites (consensus: CC(A/T) 6 GG) in the genome (Schwarz-Sommer et al, 1992).…”