117,586 research outputs found
MADS on the move : a study on MADS domain protein function and movement during floral development in Arabidopsis thaliana
No full textIn this thesis we investigated the behaviour of fluorescently-tagged MADS domain proteins during floral development in the model plant Arabidopsis thaliana, and explored the importance of intercellular transport via plasmodesmata for MADS domain transcription factor functioning. The MADS domain transcription factor family plays an important regulatory role in the development of flowers, among others by establishing the identities of the different floral organs. Although genetic screens and in vitro and in vivo studies on protein-protein and protein-DNA interactions provide important information on how MADS domain transcription factor complexes are able to regulate downstream target genes, understanding of the behaviour of MADS domain transcription factors in planta is still limited. Also, the extent to which intercellular movement of MADS domain transcription factors via plasmodesmata plays a role in developmental processes is poorly understood. Since the discovery of the GREEN FLUORESCENT PROTEIN (GFP) and the subsequent development of similar fluorescent tags, it has become possible to observe the subcellular localisation and behaviour of fluorescently-tagged proteins in living tissues with confocal laser scanning microscopy. In Chapter 2 of this thesis, different methods of tagging the MADS domain transcription factors AGAMOUS (AG), SEPALLATA3 (SEP3), and FRUITFULL (FUL) for chromatin immunoprecipitation, chromatin affinity purification and in planta imaging are described. This research shows that the addition of a small peptide tag or a fluorescent tag to MADS domain proteins easily leads to transgene silencing and specific loss-of-function mutant phenotypes, especially when the tagged MADS box genes are expressed under the control of the constitutive CaMV35S promoter. Plants that express tagged MADS box genes from genomic fragments that include all or most of the regulatory elements, and therefore mimic the natural expression pattern as much as possible, show lower levels of loss-of-function phenotypes. In addition, these plants are also more useful for investigating biological relevant behaviour of the MADS domain proteins. In Chapter 3, the spatio-temporal localisation patterns of GFP-tagged MADS domain transcription factors AG, SEP3, FUL and APETALA1 (AP1) during floral development are reported. These analyses demonstrate that there are several tissues, often epidermal cell layers, where MADS domain proteins could be detected, while the available literature describes an absence of mRNA in those tissues. This could indicate that there is intercellular transport of MADS domain proteins in meristematic tissues during floral development. The implications of the observed behaviour of the different MADS domain proteins for MADS domain protein functioning are discussed in this chapter. In Chapters 4 and 5 we describe the different methods that were used to investigate whether MADS domain proteins are indeed able to transport between cells during floral development. The difficulties that we encountered in our attempts to investigate intercellular MADS domain protein transport with microinjection techniques and by using the photoconvertible fluorescent mEosFP-tag are discussed. In plants that specifically overexpress GFP-tagged MADS domain transcription factors AG, SEP3, APETALA3 (AP3), or PISTILLATA (PI) in the epidermis, we demonstrated with a photobleaching technique that all tested proteins were able to move within the epidermal cell layer. This mechanism of lateral epidermal movement provides an explanation for most of the unexpected MADS domain protein localisations that we found in the spatio-temporal localisation analyses in Chapter 3. Additionally, we demonstrate that epidermis-expressed GFP-tagged AG is able to move from the epidermis to the subepidermis in the centre of the floral meristem, which provides proof for the suggestions that AG acts non-cell-autonomously in the floral meristem. In these plants we also analyzed the effects of epidermal MADS domain protein expression on the plant phenotype. This showed, among others, that epidermis-expressed AG is able to fully complement its own mutant background, while epidermis-expressed AP3 is not. In Chapter 6, we explore the mechanisms underlying the behaviour of GFP-tagged SEP3 during petal and stamen development that was observed in the spatio-temporal localisation studies described in Chapter 3. Just prior to the initiation of petal and stamen primordia GFP-tagged SEP3 proteins change their subcellular localisation from predominantly nuclear to more cytoplasmic, and at later stages GFP-tagged SEP3 protein seems to disappear in the middle of the primordia without the loss of SEP3 mRNA expression. These two processes could be regulated at a post-transcriptional level by two mechanisms that are discussed, namely 26s proteasome mediated SEP3 protein degradation and epidermal-oriented intercellular transport of SEP3 proteins. Additionally, we demonstrate that there are no clear indications that the observed GFP-tagged SEP3 behaviour is due to the presence of F-box protein UNUSUAL FLORAL ORGANS (UFO), which regulates petal and stamen development. In Chapter 7, this thesis finishes with some concluding remarks on in planta imaging of MADS domain transcription factors and the possible mechanisms of MADS domain protein movement in the floral meristem. Furthermore, we speculate on the importance of MADS domain protein movement in establishing MADS box gene expression patterns and MADS domain protein gradients, and on the need for symplastically isolated domains for proper floral development. <br/
Molecular control of ovule development
No full textEnormous progress has been made over the past five years in understanding the floral homeotic genes, which specify the fate of the floral organ meristems. More recently, regulatory genes have been cloned from Petunia hybrida and Arabidopsis thaliana that play essential roles in the development of the ovule - the floral organ that contains the female gametophyte. Extensive mutagenesis programmes using Arabidopsis have yielded a number of ovule mutants that reflect the various steps in ovule ontogeny. These mutants, and the identification of the first key regulatory genes involved in ovule development, are powerful research tools for studies on plant reproduction. Moreover, ovule development is intriguing for evolutionary studies, because the ovule is a relatively simple organ found in both modern angiosperms and gymnosperms, and their common ancestor
In planta localisation patterns of MADS domain proteins during floral development in Arabidopsis thaliana
No full textBackground: MADS domain transcription factors play important roles in various developmental processes in flowering plants. Members of this family play a prominent role in the transition to flowering and the specification of floral organ identity. Several studies reported mRNA expression patterns of the genes encoding these MADS domain proteins, however, these studies do not provide the necessary information on the temporal and spatial localisation of the proteins. We have made GREEN FLUORESCENT PROTEIN (GFP) translational fusions with the four MADS domain proteins SEPALLATA3, AGAMOUS, FRUITFULL and APETALA1 from the model plant Arabidopsis thaliana and analysed the protein localisation patterns in living plant tissues by confocal laser scanning microscopy (CLSM). Results: We unravelled the protein localisation patterns of the four MADS domain proteins at a cellular and subcellular level in inflorescence and floral meristems, during development of the early flower bud stages, and during further differentiation of the floral organs. The protein localisation patterns revealed a few deviations from known mRNA expression patterns, suggesting a non-cell autonomous action of these factors or alternative control mechanisms. In addition, we observed a change in the subcellular localisation of SEPALLATA3 from a predominantly nuclear localisation to a more cytoplasmic localisation, occurring specifically during petal and stamen development. Furthermore, we show that the down-regulation of the homeodomain transcription factor WUSCHEL in ovular tissues is preceded by the occurrence of both AGAMOUS and SEPALLATA3 proteins, supporting the hypothesis that both proteins together suppress WUSCHEL expression in the ovule. Conclusion: This approach provides a highly detailed in situ map of MADS domain protein presence during early and later stages of floral development. The subcellular localisation of the transcription factors in the cytoplasm, as observed at certain stages during development, points to mechanisms other than transcriptional control. Together this information is essential to understand the role of these proteins in the regulatory processes that drive floral development and leads to new hypotheses
Continuous-time modeling of cell fate determination in Arabidopsis flowers
Get PDFBackground The genetic control of floral organ specification is currently being investigated by various approaches, both experimentally and through modeling. Models and simulations have mostly involved boolean or related methods, and so far a quantitative, continuous-time approach has not been explored. Results We propose an ordinary differential equation (ODE) model that describes the gene expression dynamics of a gene regulatory network that controls floral organ formation in the model plant Arabidopsis thaliana. In this model, the dimerization of MADS-box transcription factors is incorporated explicitly. The unknown parameters are estimated from (known) experimental expression data. The model is validated by simulation studies of known mutant plants. Conclusions The proposed model gives realistic predictions with respect to independent mutation data. A simulation study is carried out to predict the effects of a new type of mutation that has so far not been made in Arabidopsis, but that could be used as a severe test of the validity of the model. According to our predictions, the role of dimers is surprisingly important. Moreover, the functional loss of any dimer leads to one or more phenotypic alterations
Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved?
No full textThis review illuminates extracellular electron transfer mechanisms that may be involved in microbial bioelectrochemical systems with biocathodes. Microbially-catalyzed cathodes are evolving for new bioprocessing applications for waste(water) treatment, carbon dioxide fixation, chemical product formation, or bioremediation. Extracellular electron transfer processes in biological anodes, were the electrode serves as electron acceptor, have been widely studied. However, for biological cathodes the question remains: what are the biochemical mechanisms for the extracellular electron transfer from a cathode (electron donor) to a microorganism? This question was approached by not only analysing the literature on biocathodes, but also by investigating known extracellular microbial oxidation reactions in environmental processes. Here, it is predicted that in direct electron transfer reactions, c-type cytochromes often together with hydrogenases play a critical role and that, in mediated electron transfer reactions, natural redox mediators, such as PQQ, will be involved in the bioelectrochemical reaction. These mechanisms are very similar to processes at the bioanode, but the components operate at different redox potentials. The biocatalyzed cathode reactions, thereby, are not necessarily energy conserving for the microorganism. © 2010 Elsevier Ltd
Sex-determination in the monoecius species cucumber is confined to specific floral whorls
No full textIn unisexual flowers, sex is determined by the selective repression of growth or the abortion of either male or female reproductive organs. The mechanism by which this process is controlled in plants is still poorly understood. Because it is known that the identity of reproductive organs in plants is controlled by homeotic genes belonging to the MADS box gene family, we analyzed floral homeotic mutants from cucumber, a species that bears both male and female flowers on the same individual. To study the characteristics of sex determination in more detail, we produced mutants similar to class A and C homeotic mutants from well-characterized hermaphrodite species such as Arabidopsis by ectopically expressing and suppressing the cucumber gene CUCUMBER MADS1 (CUM1). The cucumber mutant green petals (gp) corresponds to the previously characterized B mutants from several species and appeared to be caused by a deletion of 15 amino acid residues in the coding region of the class B MADS box gene CUM26. These homeotic mutants reveal two important concepts that govern sex determination in cucumber. First, the arrest of either male or female organ development is dependent on their positions in the flower and is not associated with their sexual identity. Second, the data presented here strongly suggest that the class C homeotic function is required for the position-dependent arrest of reproductive organs
MADS box genes expressed in developing inflorescences of rice and sorghum
No full textWith the aim of elucidating the complex genetic system controlling flower morphogenesis in cereals, we have characterized two rice and two sorghum MADS box genes isolated from cDNA libraries made from developing inflorescences. The rice clones OsMADS24 and OsMADS45, which share high homology with the Arabidopsis AGL2 and AGL4 MADS box genes, are expressed in the floral meristem, in all the primordia, and in mature floral organs. High expression levels have also been found in developing kernels. The sorghum clone SbMADS1 is also homologous to AGL2 and AGL4: expression analysis and mapping data suggest that it is the ortholog of OsMADS24. The pattern of expression of SbMADS2, the other sorghum MADS box gene, suggests that it may play a role as a meristem identity gene, as does AP1 in Arabidopsis, to which it shows considerable homology. The four genes have been mapped on a rice RFLP genetic map: the results are discussed in terms of synteny among cereals
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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