Publicação
Evolution of the gene regulatory network controlling flower dorsoventral asymmetry
| Resumo: | The understanding of the origin and evolution of morphological novelties has been a long-standing challenge in biology. It demands the elucidation of developmental and genetic mechanisms that underlie the establishment of such new structures. In order to advance our understanding of the gene regulatory networks (GRNs) underlying novel developmental traits it is essential to study how GRN are first establish, how they evolve and what morphogenetic processes they control. Using these principles, studying traits that have evolved multiple times independently provides a means to elucidate the evolutionary and developmental processes behind adaptive trait diversification. Floral dorsoventral asymmetry is thought to have evolved many times independently in different angiosperm lineages from radially symmetric ancestors and, thus, it provides a good system to study the evolution of a GRN responsible for the establishment of a novel morphology. The establishment of flower asymmetry depends on the activities of a set of transcription regulators that act on the dorsal or ventral domains of the flower meristem. CYCLOIDEA (CYC), DICHOTOMA (DICH) and RADIALIS (RAD) are expressed in the dorsal domain of floral primordia and promote dorsal petal identity. DIV is expressed all-round the floral primordium, even though it only has a phenotypic effect in more ventral regions where it activates CUPULIFORMIS (CUP) that stimulates the production of auxin at the base of the ventral petal and enhancing its proximo-distal growth. Genetic and molecular studies have revealed that RAD is a direct target of CYC and antagonizes the activity of DIV. This was further explored by using a yeast two-hybrid screening, which led to the identification of two novel related MYB-like proteins DIV-and-RAD-Interacting-Factors (DRIFs) that interact with both RAD and DIV. Therefore, the DRIF proteins might also be involved in the antagonism that RAD has on DIV activity in the establishment of flower asymmetry in Antirrhinum. The aim of this thesis is primarily to understand the molecular and cellular mechanisms by which the transcription factors DIV, RAD and DRIF interact in order to generate an asymmetric pattern of gene activity in the flower meristem. Furthermore, to elucidate how this GRN was first established and evolved, the molecular origin and evolution of the DIV, DRIF and RAD (DDR) regulatory module were investigated. To unravel other morphogenetic mechanisms underlying the development of the complex Antirrhinum flower shape it was analyzed which genes are downstream of the DIV-DRIF complex that drive the development of the ventral petal. Furthermore, the function of the DRIF homologs in Arabidopsis, the AtDRIF genes, was also studied in order to give insights into potential roles of the DRIF family in a species with symmetrical flowers. Our results suggest that in the dorsal region of the Antirrhinum flower meristem the dorsal protein RAD antagonizes the activity of the ventral identity protein DIV in a subcellular competition for a DRIF protein, promoting the establishment of the asymmetric pattern of gene activity in the Antirrhinum flower. Results from the study of the evolution of the DDR transcription module indicate that the MYB domain, through which the DIV, DRIF and RAD proteins interact, had a common evolutionary origin from an older MYB domain. Although the DIV and DRIF protein families have appeared before the evolution of the green algae, interactions between the DIV and DRIF proteins are only detected in the seed plants. Moreover, the RAD-DRIF interaction is first detected in ancient angiosperms, despite of the presence of RAD genes in gymnosperms. In Arabidopsis, a species with symmetrical flowers, we show that the AtDRIF genes have a role in flower induction under long days and regulate hypocotyl elongation and apical hook development. The similarity between the phenotype of the AtDRIFs mutant and the lines overexpressing several RAD homologs in Arabidopsis indicates that the AtRADs might be antagonizing the activity of the AtDRIFs in a mechanism which resembles the molecular interaction between the RAD and DRIF proteins in Antirrhinum. The DIV-DRIF transcription complex has most likely been recruited in Antirrhinum to regulate the shaping of the ventral petal. We show that this function might have been established by recruiting a set of genes, which in Arabidopsis are responsible for modulating the development of primordia outgrowth, to act as spatiotemporal regulators of CUP expression during the development of the flower to shape its complex form. Taken together, this thesis provides a deeper understanding on the molecular mechanisms underlying the establishment and evolution of GRNs responsible for the development of new biological forms and functions. |
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| Autores principais: | Raimundo, João Alexandre Pereira |
| Assunto: | Ciências Naturais::Ciências Biológicas |
| Ano: | 2015 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso restrito |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The understanding of the origin and evolution of morphological novelties has been a long-standing challenge in biology. It demands the elucidation of developmental and genetic mechanisms that underlie the establishment of such new structures. In order to advance our understanding of the gene regulatory networks (GRNs) underlying novel developmental traits it is essential to study how GRN are first establish, how they evolve and what morphogenetic processes they control. Using these principles, studying traits that have evolved multiple times independently provides a means to elucidate the evolutionary and developmental processes behind adaptive trait diversification. Floral dorsoventral asymmetry is thought to have evolved many times independently in different angiosperm lineages from radially symmetric ancestors and, thus, it provides a good system to study the evolution of a GRN responsible for the establishment of a novel morphology. The establishment of flower asymmetry depends on the activities of a set of transcription regulators that act on the dorsal or ventral domains of the flower meristem. CYCLOIDEA (CYC), DICHOTOMA (DICH) and RADIALIS (RAD) are expressed in the dorsal domain of floral primordia and promote dorsal petal identity. DIV is expressed all-round the floral primordium, even though it only has a phenotypic effect in more ventral regions where it activates CUPULIFORMIS (CUP) that stimulates the production of auxin at the base of the ventral petal and enhancing its proximo-distal growth. Genetic and molecular studies have revealed that RAD is a direct target of CYC and antagonizes the activity of DIV. This was further explored by using a yeast two-hybrid screening, which led to the identification of two novel related MYB-like proteins DIV-and-RAD-Interacting-Factors (DRIFs) that interact with both RAD and DIV. Therefore, the DRIF proteins might also be involved in the antagonism that RAD has on DIV activity in the establishment of flower asymmetry in Antirrhinum. The aim of this thesis is primarily to understand the molecular and cellular mechanisms by which the transcription factors DIV, RAD and DRIF interact in order to generate an asymmetric pattern of gene activity in the flower meristem. Furthermore, to elucidate how this GRN was first established and evolved, the molecular origin and evolution of the DIV, DRIF and RAD (DDR) regulatory module were investigated. To unravel other morphogenetic mechanisms underlying the development of the complex Antirrhinum flower shape it was analyzed which genes are downstream of the DIV-DRIF complex that drive the development of the ventral petal. Furthermore, the function of the DRIF homologs in Arabidopsis, the AtDRIF genes, was also studied in order to give insights into potential roles of the DRIF family in a species with symmetrical flowers. Our results suggest that in the dorsal region of the Antirrhinum flower meristem the dorsal protein RAD antagonizes the activity of the ventral identity protein DIV in a subcellular competition for a DRIF protein, promoting the establishment of the asymmetric pattern of gene activity in the Antirrhinum flower. Results from the study of the evolution of the DDR transcription module indicate that the MYB domain, through which the DIV, DRIF and RAD proteins interact, had a common evolutionary origin from an older MYB domain. Although the DIV and DRIF protein families have appeared before the evolution of the green algae, interactions between the DIV and DRIF proteins are only detected in the seed plants. Moreover, the RAD-DRIF interaction is first detected in ancient angiosperms, despite of the presence of RAD genes in gymnosperms. In Arabidopsis, a species with symmetrical flowers, we show that the AtDRIF genes have a role in flower induction under long days and regulate hypocotyl elongation and apical hook development. The similarity between the phenotype of the AtDRIFs mutant and the lines overexpressing several RAD homologs in Arabidopsis indicates that the AtRADs might be antagonizing the activity of the AtDRIFs in a mechanism which resembles the molecular interaction between the RAD and DRIF proteins in Antirrhinum. The DIV-DRIF transcription complex has most likely been recruited in Antirrhinum to regulate the shaping of the ventral petal. We show that this function might have been established by recruiting a set of genes, which in Arabidopsis are responsible for modulating the development of primordia outgrowth, to act as spatiotemporal regulators of CUP expression during the development of the flower to shape its complex form. Taken together, this thesis provides a deeper understanding on the molecular mechanisms underlying the establishment and evolution of GRNs responsible for the development of new biological forms and functions. |
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