Evolution and Development of the Seed Coat in Gymnosperms

Gymnosperms and angiosperms are the most abundant plant lineages on earth and constitute a turning point in the evolution of plants because they are at the origin of the seed, a key morphological and developmental novelty in the evolution of land plant. Although the morphological variation of the seed, across seed plants, may on its own, explain the complexity of this structure, the origin, and evolution are even more, the understanding of these topics is still under discussion. Evidence shows that previous studies have often lacked the component of gene expression, particularly in species that are not model species. The gene expression approach is key to have access to information on the putative functional evolution of the genetic network involved in the development of the seed coat, the object of this research. Therefore, in a comparative context, this thesis, focused on different species of gymnosperms: Gnetum gnemon, Ginkgo biloba, Ephedra californica, Ephedra antisyphilitica and Taxux baccata, addresses the evolution and development of the seed coat through morphological, anatomical, phylogenetic, and genomic perspectives. In the first part, the subject is approached by a review of what is known about the genes that are involved in the development of the ovule in angiosperms (Chapter 1), followed by analyses of gene expression in Gnetum and Ginkgo (Chapter 2 ). The gene expression analyses performed for the homologs of Ginkgo and Gnetum: WUS, ANT, BELL1, KAN and UCN, made it possible to determine that BEL1 and KAN, also studied in seedless plants, are found expressed in sporangia. These results indicate that: most of these genes have undergone multiple duplication events and, that the expression patterns are not conserved across seed plants; results that support the hypothesis of the evolution of the integuments as result of sterilization of sporangia. A second component of this thesis explores through transcriptome analyses, the genes likely involved in the development of structures forming part of the integument/ seed coat in Ginkgo (Chapter 3 ) and seed coat structures such as the fleshy and dry bracts in Ephedra antisyphilitica and Ephedra californica, respectively (Chapter 4), and the aril of Taxus baccata (Chapter 5 ). This work evidences the complexity of the genetic network underlying the development of the integument and seed coat across seed plants, while emphasizing the importance of studies in non-model species. Moreover, the transcriptome analyses here presented, focusing on the seed coat of species from different groups of seed plants, provide a solid basis for understanding this important and yet enigmatic structure