Separation of genetic functions controlling organ identity in flowers (original) (raw)
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THE PLANT CELL ONLINE, 1995
The unusual floral organs (ufo) mutant of Arabidopsis has flowers with variable homeotic organ transformations and inflorescence-like characteristics. To determine the relationship between UFO and previously characterized meristem and organ identity genes, we cloned UFO and determined its expression pattern. The UFO gene shows extensive homology with FlMBRlATA (FIM), a gene mediating between meristem and organ identity genes in Antirrhinum. All three UFO mutant alleles that we sequenced are predicted to produce truncated proteins. UFO transcripts were first detected in early floral meristems, before organ identity genes had been activated. At later developmental stages, UFO expression is restricted to the junction between sepal and petal primordia. Phenotypic, genetic, and expression pattern comparisons between UFO and FIM suggest that they are cognate homologs and play a similar role in mediating between meristem and organ identity genes. However, some differences in the functions and genetic interactions of UFO and FIM were apparent, indicating that changes in partially redundant pathways have occurred during the evolutionary divergence of Arabidopsis and Antirrhinum.
Plant Biotechnology, 2010
Floral organ development is an important part of the plant life cycle. In angiosperms, floral organs are formed in concentric rings, called whorls. Sepals are formed first in the outer whorl (whorl 1), followed by petals, stamens, and carpels in whorl 2, 3 and 4 of flower, respectively. According to the ABC model of floral patterning that has been proposed by Coen and Meyerowitz in 1991, class B genes are important for establishing petals (together with class A genes) and stamens (together with class C genes) (Coen and Meyerowitz 1991). All of class B genes belong to the MIKC-type MADS-box gene family of transcription factors, which include a highly conserved region called a MADS domain, an intervening (I) domain, a keratin-like coiled-coil (K) domain, and a C-terminal domain (Shore and Sharrocks 1995). Duplication of an ancestral B gene during plant evolution gave rise to two class B subfamilies, APETALA3/ DEFICIENS (AP3/DEF) and PISTILLATA/GLOBOSA (PI/GLO) (Goto and Meyerowitz 1994; Jazk et al. 1994; Kramer et al. 1998 Schwarz-Sommer et al. 1992). The multiple gene duplication took place in the AP3/DEF lineage, causes separation of three distinct clades with divergent C-terminal motifs: euAP3, paleoAP3, and TOMATO MADS-BOX GENE6 (TM6) (Kramer et al. 1998; Theissen et al. 1996). The euAP3 clade is composed of AP3/DEF-like genes isolated from higher eudicots, whereas genes belonging to the paleoAP3 clade have been identified in lower eudicots, magnolid dicots, monocots, and basal angiosperms (Kramer and Irish 2000). The genes in the TM6 clade are present in higher dicots and monocots, the expression patterns and functions of the genes in this clade are more diverse than those in the class-B MADS-box family (Pnueli et al. 1991; Yu et al. 1999). In Antirrhinum, DEF and GLO proteins are function in cells as heterodimeric complexes (Tröbner et al. 1992) and can be integrated into a tetrameric protein complex together with a class E protein; SEPALLATA 3 (SEP3) (Melzer et al. 2009). Functions of class B genes have been largely confirmed in several species of core-eudicot plants, the results
Epidermal control of floral organ identity by class B homeotic genes in Antirrhinum and Arabidopsis
Development (Cambridge, England), 2001
To assess the contribution of the epidermis to the control of petal and stamen organ identity, we have used transgenic Antirrhinum and Arabidopsis plants that expressed the Antirrhinum class B homeotic transcription factors DEFICIENS (DEF) and GLOBOSA (GLO) in the epidermis. Transgene expression was controlled by the ANTIRRHINUM FIDDLEHEAD (AFI) promoter, which directs gene expression to the L1 meristematic layer and, later, to the epidermis of differentiating organs. Transgenic epidermal DEF and GLO chimeras display similar phenotypes, suggesting similar epidermal contributions by the two class B genes in ANTIRRHINUM: Epidermal B function autonomously controls the differentiation of Antirrhinum petal epidermal cell types, but cannot fully control the pattern of cell divisions and the specification of sub-epidermal petal cell-identity by epidermal signalling. This non-autonomous control is enhanced if the endogenous class B genes can be activated from the epidermis. The developmenta...
Conservation of Floral Homeotic Gene Function between Arabidopsis and Antirrhinum
The Plant Cell, 1995
Severa1 homeotic genes controlling floral development have been isolated in both Antirrhinum and Arabidopsis. Based on the similarities in sequence and in the phenotypes elicited by mutations in some of these genes, it has been proposed that the regulatory hierarchy controlling floral development is comparable in these two species. We have performed a direct experimental test of this hypothesis by introducing a chimeric Antirrhinum Deficiens (DefA)/Arabidopsis APETALA3 (AP3) gene, under the control of the Arabidopsis AP3 promoter, into Arabidopsis. We demonstrated that this transgene is sufficient to partially complement severe mutations at the AP3 locus. In combination with a weak ap3 mutation, this transgene is capable of completely rescuing the mutant phenotype to a fully functional wild-type flower. These observations indicate that despite differences in DNA sequence and expression, DefA coding sequences can compensate for the loss of AP3 gene function. We discuss the implications of these results for the evolution of homeotic gene function in flowering plants.
Genetic basis for innovations in floral organ identity
Journal of Experimental Zoology …, 2005
Of the many innovations associated with the radiation of the angiosperms, the evolution of a petal identity program is among the best understood from a genetic standpoint. Although the existing data do indicate that similar genetic mechanisms control petal development across diverse taxa, there is also considerable evidence for variability in petal identity programs, likely due to a number of factors. These points are illustrated through a review of our current knowledge on the subject, integrating phylogenetic, morphological, and genetic studies. Comparative studies of petal identity highlight the complex nature of homology in plants and stand as a cautionary tale for the interpretation of gene expression data.
The Plant Cell, 2013
The floral organ identity factor AGAMOUS (AG) is a key regulator of Arabidopsis thaliana flower development, where it is involved in the formation of the reproductive floral organs as well as in the control of meristem determinacy. To obtain insights into how AG specifies organ fate, we determined the genes and processes acting downstream of this C function regulator during early flower development and distinguished between direct and indirect effects. To this end, we combined genome-wide localization studies, gene perturbation experiments, and computational analyses. Our results demonstrate that AG controls flower development to a large extent by controlling the expression of other genes with regulatory functions, which are involved in mediating a plethora of different developmental processes. One aspect of this function is the suppression of the leaf development program in emerging floral primordia. Using trichome initiation as an example, we demonstrate that AG inhibits an important aspect of leaf development through the direct control of key regulatory genes. A comparison of the gene expression programs controlled by AG and the B function regulators APETALA3 and PISTILLATA, respectively, showed that while they control many developmental processes in conjunction, they also have marked antagonistic, as well as independent activities.