MADS-Box Gene Phylogeny and the Evolution of Plant Form Characterisation of a Family of Regulators of Reproductive Development from the Conifer Norway Spruce, Picea abies

Sammanfattning: The evolutionary relationships between the angiosperm floral organs and the reproductive organs of other seed plants is not known. Flower organ development requires transcription factors encoded by the MADS-box genes. Since the evolution of novel morphology likely involve changes in developmental regulators, I have analysed MADS-box genes from the conifer Norway spruce, Picea abies, a representative of the gymnosperm group of seed plants.The results show that the MADS-box gene family has evolved via gene duplications and subsequent diversifications in correlation in time with the evolution of morphological novelties along the seed-plant lineage.Angiosperm MADS-box genes that determine petal and stamen development have homologues in the conifers, that are specifically active in pollen cones. It is, therefore, likely that the common ancestor of these genes controlled the development of the pollen-bearing organs in the early seed plants, and later were recruited for petal development in the angiosperms.Norway spruce set cones at an age of 15-20 years. One of the spruce MADS-box genes analysed may have a function in the control of the transition to reproductive phase, supported by expression data and the effect of the gene on development of transgenic Arabidopsis plants.Two of the spruce genes identified are not closely related to any known angiosperm gene. These may have roles in gymnosperm-specific developmental processes, possibly in the patterning of the conifer cones, as suggested by their expression patterns.The molecular regulation of cone- and flower development in fundamental aspects is highly conserved between conifers and angiosperms, however, differences detected may be informative regarding the origin of morphological complexity.