Molecular approaches to the developmental biology of Norway spruce, Picea abies

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.