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- Groth, Erika, 1980-
(författare)
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Functional Diversification among MADS-Box Genes and the Evolution of Conifer Seed Cone Development
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- MADS-box genes are important regulators of reproductive development in seed plants, including both flowering plants and conifers. In this thesis the evolution of the AGAMOUS subfamily of MADS-box genes, and what the ancestral function of this group of genes might have been in the early seed plants about 300 million years ago, was addressed by the discovery of two novel conifer genes, both basal to all previously known AGAMOUS subfamily genes. DAL20, the most basal of these genes, was exclusively expressed in roots, unlike all previously known AGAMOUS subfamily genes. I also studied the evolutionary mechanisms leading to functional diversification of duplicated genes in two different subfamilies of MADS-box genes; the AGAMOUS and AGL6 subfamilies. Focus was on studying changes in gene expression pattern, representing changes in the transcriptional regulation between the genes, and on comparing the functional properties of the gene products, representing changes in the protein-coding sequence between the genes. Duplicated genes in the AGL6 subfamily were found to have evolved by both mechanisms. In the AGAMOUS subfamily I found duplicated spruce genes; DAL2 and DAL20, that appear to have functionally diversified mainly by changes in the transcriptional regulation. Conifer AGAMOUS subfamily genes were also used in a comparative developmental-genetics approach to evaluate hypotheses, based on the morphology of fossil and extant conifer seed cones, on the identity of the female reproductive organ, the ovuliferous scale, and the evolution of seed cone morphology in the conifer families Pinaceae, Taxodiaceae and Cupressaceae. Seed cones in these families have been hypothesized to have homologous ovule-bearing organs, but I found substantial differences in the expression patterns of orthologous AGAMOUS subfamily genes in seed cones of these families that are not compatible with this hypothesis, indicating that the evolutionary history of conifer seed cones is more diverse than previously thought.
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| 2. |
- Tandre, Karolina
(författare)
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Molecular approaches to the developmental biology of Norway spruce, Picea abies
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ontogeny depends on the developmental control of genes. In this thesis twoapproaches were taken to identify genes essential to developmental processes inthe conifer Norway spruce, Picea abies (L.) Karst. Firstly, development of vegetative meristems was studied in a model system for de novo formation ofmeristems on zygotic embryos in vitro, induced by a cytokinin treatment. As areference process germinative development was analysed. By differentialscreening, clones representing genes with differential expression in relation tothese processes were isolated. Meristem induction quantitatively affected the expression of genes which had a differential expression pattern in relation togermination. Genes coding for histone H2A, α-tubulin, chlorophyll a/b bindingprotein, chloroplast ribosomal protein S7, polyubiquitin and β-1,3-glucanase wereidentified. None of the cloned genes were active specifically in developingmeristems, their differential expression instead reflecting activity in dividing versuselongating and differentiating cells. Expression of the histone H2A gene wastightly linked to cell proliferation. In contrast, the expression of a sprucehomologue to the cell cycle control gene CDC2, was not strictly coupled to cellproliferation.In the second part of the work the development of reproductive organs wasapproached by taking advantage of recent results on angiosperm flowerontogeny. Flower development is controlled by MADS-box genes, coding fortranscription factors. Three MADS-box genes, DAL1, DAL2 and DAL3, wereisolated from spruce. A phylogenetic analyses, based on primary sequence,identified DAL2 as structurally most closely related to class C MADS-box genescontrolling carpel and stamen identity in angiosperms and suggested that thelast common ancestor of conifers and angiosperms had at least three differentMADS-box genes. DAL2 was expressed only in cones. In the female coneDAL2 expression was detected specifically in ovuliferous scales, but not insterile bracts. In transgenic Arabidopsis thaliana DAL2 caused homeotictransformations of flower organs, previously recorded specifically forangiospermclass C MADS-box genes. Thus, DAL2 and class C genes likelyshare a common origin and have a conserved function in control of ontogeny ofthe ovule-bearing organs in conifers and angiosperms.
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