Publicação
Molecular characterization of flower development of Quercus suber L
| Resumo: | Quercus suber, or cork oak, is an important forest species in Southern Europe and Northern Africa. This perennial monoecious species has an accentuated protandrous system: in late winter, and sometimes in autumn, male flowers develop in catkins that emerge close to the dormant buds. Female flowers develop in spring (4 to 8 weeks after male flowering) in a process that takes more than one month to full completion. Both male and female flowers are unisexual at inception with no evidence of aborted sexual organs. Cork oak has also a long juvenile phase and a long progamic phase. The progamic phase is characterized by the arrest of pollen tube growth that lasts until the full development of the embryo sac. Despite the importance of this species (economical and ecological), very little is known regarding the genetic mechanisms involved in cork oak reproduction mainly due to the lack of molecular resources that has hampered the ability to perform functional studies in this species. The main aim of this thesis was the study of the reproductive characteristics of Q. suber using distinct molecular approaches. Non-normalised cDNA libraries of male and female flowers were generated using 454 pyrosequencing technology in order to identify differentially expressed genes during the development of male and female flowers of Q. suber. Comparative analysis of the transcriptomes revealed genes differentially expressed in early and late stages of development of female and male flowers, some of which are involved in flower development of other species. These differentially expressed genes included MADS-box genes homologous to the regulatory floral homeotic genes (ABCDE model). The temporal expression of these genes (some are sex-biased) and the identification of new protein-protein interactions suggest that the development of unisexual flowers of Q. suber may be under control of specific changes in the dynamics of the ABCDE model. The cork oak pronounced protandric nature was further studied by identifying the flowering induction events during the reproductive season. Expression of Q. suber homologues of recognized flower inducers suggests that male and female flower primordia are established at different time points in the growing season. Female flowers are induced in spring after bud dormancy break, whereas male flowers are induced in late summer before the establishment of bud dormancy, but fully develops in late winter, which implies a long anthesis period that spans dormancy. The establishment of two flower induction periods separated by a long anthesis period might explain abnormal flowering events that are common in Q. suber and other dichogamic species, such as the display of only one type of flower in one or successive reproductive seasons. The changes that occur during male and female reproductive organs development were further characterised during the relatively long cork oak progamic phase. The distribution of Arabinogalactan-Proteins (AGPs) and pectin epitopes was characterized in anthers and pistils. AGP genes involved in cork oak flower development were also identified. The selective labeling obtained with monoclonal antibodies during Q. suber reproductive organs development, shows that AGPs and pectins are good markers for mapping male and female gametophytic cell lineages in this species. Several cork oak AGP genes were classified as predominantly male or female based on their expression in the flowers. The functional role of these AGP genes in other species suggests that AGPs play a significant role in cork oak reproduction. Taken together, this thesis provides a deeper understanding on distinct reproductive characteristics of Q. suber. Furthermore, the mechanisms here described serve as platform to explain molecular events controlling flower development of a wide range of other angiosperm species with similar reproductive habits. |
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| Autores principais: | Sobral, Rómulo Sacramento |
| Ano: | 2017 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Quercus suber, or cork oak, is an important forest species in Southern Europe and Northern Africa. This perennial monoecious species has an accentuated protandrous system: in late winter, and sometimes in autumn, male flowers develop in catkins that emerge close to the dormant buds. Female flowers develop in spring (4 to 8 weeks after male flowering) in a process that takes more than one month to full completion. Both male and female flowers are unisexual at inception with no evidence of aborted sexual organs. Cork oak has also a long juvenile phase and a long progamic phase. The progamic phase is characterized by the arrest of pollen tube growth that lasts until the full development of the embryo sac. Despite the importance of this species (economical and ecological), very little is known regarding the genetic mechanisms involved in cork oak reproduction mainly due to the lack of molecular resources that has hampered the ability to perform functional studies in this species. The main aim of this thesis was the study of the reproductive characteristics of Q. suber using distinct molecular approaches. Non-normalised cDNA libraries of male and female flowers were generated using 454 pyrosequencing technology in order to identify differentially expressed genes during the development of male and female flowers of Q. suber. Comparative analysis of the transcriptomes revealed genes differentially expressed in early and late stages of development of female and male flowers, some of which are involved in flower development of other species. These differentially expressed genes included MADS-box genes homologous to the regulatory floral homeotic genes (ABCDE model). The temporal expression of these genes (some are sex-biased) and the identification of new protein-protein interactions suggest that the development of unisexual flowers of Q. suber may be under control of specific changes in the dynamics of the ABCDE model. The cork oak pronounced protandric nature was further studied by identifying the flowering induction events during the reproductive season. Expression of Q. suber homologues of recognized flower inducers suggests that male and female flower primordia are established at different time points in the growing season. Female flowers are induced in spring after bud dormancy break, whereas male flowers are induced in late summer before the establishment of bud dormancy, but fully develops in late winter, which implies a long anthesis period that spans dormancy. The establishment of two flower induction periods separated by a long anthesis period might explain abnormal flowering events that are common in Q. suber and other dichogamic species, such as the display of only one type of flower in one or successive reproductive seasons. The changes that occur during male and female reproductive organs development were further characterised during the relatively long cork oak progamic phase. The distribution of Arabinogalactan-Proteins (AGPs) and pectin epitopes was characterized in anthers and pistils. AGP genes involved in cork oak flower development were also identified. The selective labeling obtained with monoclonal antibodies during Q. suber reproductive organs development, shows that AGPs and pectins are good markers for mapping male and female gametophytic cell lineages in this species. Several cork oak AGP genes were classified as predominantly male or female based on their expression in the flowers. The functional role of these AGP genes in other species suggests that AGPs play a significant role in cork oak reproduction. Taken together, this thesis provides a deeper understanding on distinct reproductive characteristics of Q. suber. Furthermore, the mechanisms here described serve as platform to explain molecular events controlling flower development of a wide range of other angiosperm species with similar reproductive habits. |
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