Genetic regulation of flower development

Flower development provides a model system to study mechanisms that govern pattern formation in plants. Most flowers consist of four organ types that are present in a specific order from the periphery to the centre of the flower. Reviewed here are studies on flower development in two model species:Arabidopsis thaliana andAntirrhinum majus that focus on the molecular genetic analysis of homeotic mutations affecting pattern formation in the flower. Based on these studies a model was proposed that explains how three classes of regulatory genes can together control the development of the correct pattern of organs in the flower. The universality of the basic tenets of the model is apparent from the analysis of the homologues of theArabidopsis genes from other plant species     

The genetic and molecular mechanisms of motor neuron disease

Significant progress has been made in the identification of genes and chromosomal loci associated with several types of motor neuron disease. Of particular interest is recent work on the pathogenic mechanisms underlying these diseases, especially studies in in vitro model systems and in transgenic and gene-targeted mice.     

Genetic and molecular analyses of motoneuron development

Motoneurons have distinct identities and muscle targets. Recent classical and molecular genetic studies in flies and vertebrates have begun to elucidate how motoneuron identities and target specificities are established. Many of the same molecules participate in the guidance of both vertebrate and fly motor axons. It is less clear, however, whether the same molecular mechanisms establish vertebrate and fly motoneuron identities.     

Genetic and molecular mechanisms of pattern formation inArabidopsis flower development

One of the great unanswered questions in the biology of both plants and animals is “How do simple groups of embryonic cells develop into complex and highly structured organisms, or parts of organisms?” The answers are only beginning to be known; the processes involved include establishment of positional information, and its interpretation into patterns of cell division and cellular differentiation. One remarkable and attractive example of the formation of a complex structure from a simple group of cells is the development of a flower, with its characteristic types, numbers and patterns of floral organs. Because of the ease with which plants (especially the plantArabidopsis thaliana) can be manipulated in the laboratory, flowers provide a unique opportunity to learn some of the fundamental rules of development.     

Toward the development of DNA vaccines

DNA vaccination has proved to be a generally applicable technology in various preclinical animal models of infectious and noninfectious disease and several DNA vaccines have now entered phase I human clinical trials. It is too early to predict the effectiveness of DNA vaccines in humans and whether improved formulations of DNA vaccines will be required but several lines of investigation have suggested ways in which DNA vaccines may be improved, such as increases in expession, facilitation of DNA targeting or uptake, and enhancement of immune responses.     

Neutral theory of molecular evolution

DNA sequence data are generally interpreted as favouring Kimura's neutral theory but not without dissent and often with a great deal of controversy with respect to molecular clocks, DNA polymorphism, adaptive evolution, and gene genealogy. Although the theory serves as a guiding principle, many issues concerning mutation, recombination, and selection remain unsettled. Of particular importance is the need for more knowledge about the function and structure of molecules.     

Informatics - genome and genetic databases

Databases for biologists are becoming increasingly important. Some of these can be regarded as ‘core’ resources, such as the bibliographic databases, whereas others are of greater interest to specialists. As comparative genomics develops, however, even databases limited in their scope (e.g. to a single organism) are of great interest to a wider community.     

Glutamine repeats and inherited neurodegenerative diseases: molecular aspects

Several dominantly inherited, late onset, neurodegenerative diseases are due to expansion of CAG repeats, leading to expansion of glutamine repeats in the affected proteins. These proteins are of very different sizes and, with one exception, show no sequence homology to known proteins or to each other; their functions are unknown. In some, the glutamine repeat starts near the N-terminus, in another near the middle and in another near the C-terminus, but regardless of these differences, no disease has been observed in individuals with fewer than 37 repeats, and absence of disease has never been found in those with more than 41 repeats. Protein constructs with more than 41 repeats are toxic to E. coli and to CHO cells in culture, and they elicit ataxia in transgenic mice. These observations argue in favour of a distinct change of structure associated with elongation beyond 37–41 glutamine repeats. The review describes experiments designed to find out what these structures might be and how they could influence the properties of the proteins of which they form part. Poly- -glutamines form pleated sheets of β-strands held together by hydrogen bonds between their amides. Incorporation of glutamine repeats into a small protein of known structure made it associate irreversibly into oligomers. That association took place during the folding of the protein molecules and led to their becoming firmly interlocked by either strand- or domain-swapping. Thermodynamic considerations suggest that elongation of glutamine repeats beyond a certain length may lead to a phase change from random coils to hydrogen-bonded hairpins. Possible mechanisms of expansion of CAG repeats are discussed in the light of looped DNA model structures.     

Role of auxin in regulating Arabidopsis flower development

To elucidate the role of auxin in flower morphogenesis, its distribution patterns were studied during flower development in Arabidopsis thaliana (L.) Heynh. Expression of DR5::GUS was regarded to reflect sites of free auxin, while immunolocalization with auxin polyclonal antibodies visualized conjugated auxin distribution. The youngest flower bud was loaded with conjugated auxin. During development, the apparent concentration of free auxin increased in gradual patterns starting at the floral-organ tip. Anthers are major sites of high concentrations of free auxin that retard the development of neighboring floral organs in both the acropetal and basipetal directions. The IAA-producing anthers synchronize flower development by retarding petal development and nectary gland activity almost up to anthesis. Tapetum cells of young anthers contain free IAA which accumulates in pollen grains, suggesting that auxin promotes pollen-tube growth towards the ovules. High amounts of free auxin in the stigma induce a wide xylem fan immediately beneath it. After fertilization, the developing embryos and seeds show elevated concentrations of auxin, which establish their axial polarity. This developmental pattern of auxin production during floral-bud development suggests that young organs which produce high concentrations of free IAA inhibit or retard organ-primordium initiation and development at the shoot tip. Electronic Supplementary Material Supplementary material is available for this article at This paper is dedicated to Orna Aloni for continuous support and management over many years.     

Changes in endogenous polyamines during flower development in two diverse species of rose

Changes in the concentrations of endogenous free, conjugated and bound polyamine were determined in petals of two different species of rose, viz. Rosa damascena and Rosa bourboniana, from small bud (stage 1) till full bloom (stage 8). High free putrescine and spermidine concentrations were associated with early stages of flower development and then decreased in R. damascena. At full bloom, the concentration of free putrescine was higher than rest of the polyamines measured. A steady increase in conjugated putrescine, spermidine and spermine was observed during entire period of flower development with predominance of conjugated putrescine at full bloom. In R. damascena the bound spermine was higher than rest of the polyamines during full bloom. In R. bourboniana, during the early stages of flower development, similar situation was observed, however, at full bloom, free spermidine concentration was higher than rest of the polyamines. In this species, the concentration of conjugated and bound spermine was higher than rest of the polyamines during full bloom. Polyamine concentrations were generally lower in the petals of R. bourboniana than R. damascena which may be due to genotypic differences. The possible roles of the observed polyamines are discussed in relation to flower development.IHBT Communication no, 0345.     

Implications of sequencing bacterial genomes for pathogenesis and vaccine development

Improvements in homology search methodology and functional predictions are being complemented by the increase in the volume of sequence data with which comparative analyses can be performed. The experimental methods needed for investigation of gene function and expression in a variety of model systems of infection continue to develop. The identification of surface-exposed microbial structures and their conservation in natural populations of pathogenic species offers prospects for developing novel vaccines. A major challenge is the development of efficient screening methods to select the most promising candidates, such as immunisation with DNA.     

The integration of microarray information in the drug development process

In the past year, microarray technologies have moved beyond the proof-of-principle stage. Microarrays are now being used for genome-wide expression monitoring, large-scale polymorphism screening and mapping, and for the evaluation of drug candidates.     

Current trends and future directions in flower development research

Flowers, the reproductive structures of the approximately 400 000 extant species of flowering plants, exist in a tremendous range of forms and sizes, mainly due to developmental differences involving the number, arrangement, size and form of the floral organs of which they consist. However, this tremendous diversity is underpinned by a surprisingly robust basic floral structure in which a central group of carpels forms on an axis of determinate growth, almost invariably surrounded by two successive zones containing stamens and perianth organs, respectively. Over the last 25 years, remarkable progress has been achieved in describing the molecular mechanisms that control almost all aspects of flower development, from the phase change that initiates flowering to the final production of fruits and seeds. However, this work has been performed almost exclusively in a small number of eudicot model species, chief among which is Arabidopsis thaliana. Studies of flower development must now be extended to a much wider phylogenetic range of flowering plants and, indeed, to their closest living relatives, the gymnosperms. Studies of further, more wide-ranging models should provide insights that, for various reasons, cannot be obtained by studying the major existing models alone. The use of further models should also help to explain how the first flowering plants evolved from an unknown, although presumably gymnosperm-like ancestor, and rapidly diversified to become the largest major plant group and to dominate the terrestrial flora. The benefits for society of a thorough understanding of flower development are self-evident, as human life depends to a large extent on flowering plants and on the fruits and seeds they produce. In this preface to the Special Issue, we introduce eleven articles on flower development, representing work in both established and further models, including gymnosperms. We also present some of our own views on current trends and future directions of the flower development field.     

Pax genes and their roles in cell differentiation and development

Members of the Pax gene family are expressed in various tissues during ontogenesis. Evidence for their crucial role in morphogenesis, organogenesis, cell differentiation and oncogenesis is provided by rodent mutants and human diseases. Additionally, recent experimental in vivo and in vitro approaches have led to the identification of molecules that interact with Pax proteins.     

A two-step procedure for coupling development and usage of a pair of human neck models

Both finite element models and multi-body models of human head-neck complex had been widely used in neck injuries analysis, as the former could be used to generate detailed stress strain information and the later could generate dynamic responses with high efficiency. Sometimes, detailed stress and strain information were hoped to be obtained more efficiently, but current methods were not effective enough when they were used to analyze responses of human head neck complex to long duration undulate accelerations. In this paper, a two-step procedure for ‘parallel’ development and ‘sequential’ usage of a pair of human head neck models was discussed. The pair of models contained a finite element model and a multi-body model, which were developed based on the coupling ‘parallel’ procedure using the same bio-realistic geometry. After being validated using available data, the pair of human neck models were applied to analyze biomechanical responses of pilot’s neck during arrested landing operation according to the ‘sequential’ procedure, because typical sustained undulate accelerations usually appeared during such processes. The results, including both kinematic and detailed biomechanical responses of human head-neck complex, were obtained with preferable efficiency. This research provided an effective way for biomechanical analysis of human head neck responses to sustained undulate accelerations.     

Structural changes in flowers ofIpomoea tricolor during flower opening and closing

Summary Examination of rib tissue of developing flower buds and flowers ofIpomoea tricolor utilizing the light and electron microscopes resulted in the identification of a group of inner epidermal cells which undergo dynamic structural changes during the two days prior to flowering, during flowering and during flower fading. Over a three-day period these cells undergo enlargement, modification of shape, reduction in wall thickness, extensive vacuolation and autophagic activity, transition from a ribosome-rich cytoplasm with stacked RER and dictyosome complexes to one with only a few isolated organelles and a limited number of ribosomes, and modification of the tonoplast membrane. In contrast, other cells of the rib vacuolate prior to flowering and exhibit no further changes. The structural changes in the inner epidermal cells suggest that they affect the turgor status of the cells and initiate the opening and eventual closing of the flower.     

Controlling cell proliferation in differentiating tissues: genetic analysis of negative regulators of G1→S-phase progression

Withdrawal from the cell cycle as cells begin to differentiate is accomplished by the downregulation of cyclin-dependent kinase activities in G₁ phase. Recent analysis of loss-of-function mutations in flies, worms, and mice has provided insight into the roles of various negative regulators of G₁ phase in developing organisms.