Evolution of genetic mechanisms regulating reproductive development in plants : Characterisation of MADS-box genes active during cone development in Norway spruce

Sammanfattning: The reproductive organs of conifers and angiosperms differ in morphology in several fundamental respects. The conifer Norway spruce (Picea abies) form pollen and seed cones from separate meristems whereas angiosperms bear bipartite flowers with sepals and petals surrounding two inner whorls of stamens and carpels. Despite these differences in morphology this thesis present data to suggest that reproductive development in conifers and angiosperms is regulated by a similar molecular mechanism. This implies an evolutionary conservation of the major mechanism for reproductive development since the origin of seed plants. Flower organ identity in angiosperms is determined by regulatory genes belonging to the MADS-box gene family of transcription factors. This thesis presents the cloning and characterisation of four novel MADS-box genes from Norway spruce. Three of these genes DAL11, DAL12 and DAL13 are most closely related to angiosperm B function genes i.e. genes required for petal and stamen development. DAL11, 12 and 13 all are specifically active in developing pollen cones, with different temporal and spatial expression pattern. Functional analysis in transgenic Arabidopsis and yeast suggest that the reproductive aspect of the B-function is conserved between conifers and angiosperms. The results also suggest that the B-function in conifers is separated into one shoot identity and one organ identity determinant. A fourth gene presented; DAL10, is specifically expressed in vegetative parts of pollen- and seed cones. Phylogenetically DAL10 is not closely related to any of the known angiosperm clades, but rather forms a separate clade with other gymnosperm genes, suggesting a gymnosperm specific function. We suggest that the DAL10 activity reflects a function in the determination of the reproductive shoot.