Missing links: the genetic architecture of flower and floral diversification (original) (raw)
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Diversification of Floral Homeotic Gene Function
HortScience, 2003
shown to also be required for specifying petal, stamen, and carpel identities, adding another layer of complexity to the ABC model (Pelaz, et al., 2000) (Fig. 1). These MADS-box gene products form ternary and quaternary complexes which could explain, at the molecular level, how these transcription factors coordinate their functions (Honma and Goto, 2001; Pelaz, et al., 2001). The expression patterns of all of these genes, with the exception of AP2 which is expressed ubiquitously throughout the flower, largely corresponds to their domains of action as postulated in the ABC model. The roles of AP3 and PI in Arabidopsis
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.
Molecular evolution of flower development
Trends in Ecology and Evolution, 2000
Flowers, as reproductive structures of the most successful group of land plants, have been a central focus of study for both evolutionists and ecologists. Recent advances in unravelling the genetics of flower development have provided insight into the evolution of floral structures among angiosperms. The study of the evolution of genes that control floral morphogenesis permits us to draw inferences on the diversification of developmental systems, the origin of floral organs and the selective forces that drive evolutionary change among these plant reproductive structures.
Separation of genetic functions controlling organ identity in flowers
The EMBO Journal, 2003
Comparative studies on the ABC model of¯oral development have revealed extensive conservation of B and C class genes, but have failed to identify similar conservation for A class genes. Using a reverse genetic approach, we show that the previous inability to obtain Antirrhinum mutants corresponding to the A class gene AP2 of Arabidopsis re¯ects greater genetic redundancy in Antirrhinum. Antirrhinum has two genes corresponding to AP2, termed LIP1 and LIP2, both of which need to be inactivated to give a mutant phenotype. Analysis of interactions between LIP and class B/C genes shows that unlike AP2 in Arabidopsis, LIP genes are not required for repression of C in outer whorls of the¯ower. However, like AP2, LIP genes play a role in sepal, petal and ovule development, although some of their detailed effects are different, re¯ecting the diverse morphologies of Antirrhinum and Arabidopsis¯owers. The dual functions for which AP2 is required in Arabidopsis are therefore separate in Antirrhinum, showing that the genetic basis of some aspects of organ identity have undergone major evolutionary change.
Flower Development: Initiation, Differentiation, and Diversification
Annual Review of Cell and Developmental Biology, 2003
▪ Flowering is one of the most intensively studied processes in plant development. Despite the wide diversity in floral forms, flowers have a simple stereotypical architecture. Flowers develop from florally determined meristems. These small populations of cells proliferate to form the floral organs, including the sterile outer organs, the sepals and petals, and the inner reproductive organs, the stamens and carpels. In the past decade, analyses of key flowering genes have been carried out primarily in Arabidopsis and have provided a foundation for understanding the underlying molecular genetic mechanisms controlling different aspects of floral development. Such studies have illuminated the transcriptional cascades responsible for the regulation of these key genes, as well as how these genes effect their functions. In turn, these studies have resulted in the refinement of the original ideas of how flowers develop and have indicated the gaps in our knowledge that need to be addressed.
Genetics of Floral Development and Patterning
Floriculture, Ornamental and Plant Biotechnology: Advances and Topical Issues Vol. I, 2006
Flowers are valued both for their beauty and their economic importance, as flower parts form the major source of food for both humans and animals. Flowers also present an intriguing model for biological pattern formation: a small group of flower meristem cells gives rise to several different organ types in stereotypical positions in rapid succession. The use of molecular genetics approaches in the study of flower development has led to a series of insights into the biological mechanisms of generating flower patterns. This review focuses on the current knowledge of the genetic basis of flower patterning in Arabidopsis thaliana. Flower patterning requires several steps: the specification of lateral meristems as flowers instead of shoots, the establishment of proper floral organ identity, and the initiation of organs in correct number and positions. Floral meristem identity genes integrate environmental cues to establish a flower program, including the activation of flower homeotic genes, which specify sepal, petal, stamen, and carpel formation. Organ initiation occurs largely independently of organ identity and requires proper control of flower meristem size, proper regulation of cell division orientation, and spacing mechanisms that remain poorly defined. Future challenges include identifying additional genes involved in establishing the flower pattern, along with identifying more genes that act downstream of patterning genes to confer the final size and shape of flower organs across diverse species.
MADS-box genes are involved in floral development and evolution
Acta biochimica Polonica, 2001
MADS-box genes encode transcription factors in all eukaryotic organisms thus far studied. Plant MADS-box proteins contain a DNA-binding (M), an intervening (I), a Keratin-like (K) and a C-terminal C-domain, thus plant MADS-box proteins are of the MIKC type. In higher plants most of the well-characterized genes are involved in floral development. They control the transition from vegetative to generative growth and determine inflorescence meristem identity. They specify floral organ identity as outlined in the ABC model of floral development. Moreover, in Antirrhinum majus the MADS-box gene products DEF/GLO and PLE control cell proliferation in the developing flower bud. In this species the DEF/GLO and the SQUA proteins form a ternary complex which determines the overall "Bauplan" of the flower. Phylogenetic reconstructions of MADS-box sequences obtained from ferns, gymnosperms and higher eudicots reveal that, although ferns possess already MIKC type genes, these are not ort...
Eucalypt MADS-Box Genes Expressed in Developing Flowers
PLANT PHYSIOLOGY, 1998
Three MADS-box genes were identified from a cDNA library derived from young flowers of Eucalyptus grandis W. Hill ex Maiden. The three egm genes are single-copy genes and are expressed almost exclusively in flowers. The egm1 and egm3 genes shared strongest homology with other plant MADS-box genes, which mediate between the floral meristem and the organ-identity genes. The egm3 gene was also expressed strongly in the receptacle or floral tube, which surrounds the carpels in the eucalypt flower and bears the sepals, petals, and numerous stamens. There appeared to be a group of genes in eucalypts with strong homology with the 3 region of the egm1 gene. The egm2 gene was expressed in eucalypt petals and stamens and was most homologous to MADSbox genes, which belong to the globosa group of genes, which regulate organogenesis of the second and third floral whorls. The possible role of these three genes in eucalypt floral development is discussed.