RESUMO
In Arabidopsis thaliana, the phytohormone auxin is an important patterning agent during embryogenesis and post-embryonic development, exerting effects through transcriptional regulation. The main determinants of the transcriptional auxin response machinery are AUXIN RESPONSE FACTOR (ARF) transcription factors and AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) inhibitors. Although members of these two protein families are major developmental regulators, the transcriptional regulation of the genes encoding them has not been well explored. For example, apart from auxin-linked regulatory inputs, factors regulating the expression of the AUX/IAA BODENLOS (BDL)/IAA12 are not known. Here, it was shown that the HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP) transcription factor HOMEOBOX PROTEIN 5 (HB5) negatively regulates BDL expression, which may contribute to the spatial control of BDL expression. As such, HB5 and probably other class I HD-ZIP proteins, appear to modulate BDL-dependent auxin response.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Regulação para Baixo , Regulação da Expressão Gênica de Plantas , Proteínas de Homeodomínio/metabolismo , Proteínas Repressoras/genética , Fatores de Transcrição/metabolismo , Arabidopsis/química , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Homeodomínio/química , Proteínas de Homeodomínio/genética , Ácidos Indolacéticos/metabolismo , Zíper de Leucina , Reguladores de Crescimento de Plantas/metabolismo , Proteínas Repressoras/metabolismo , Fatores de Transcrição/química , Fatores de Transcrição/genéticaRESUMO
Like animals, the mature plant body develops via successive sets of instructions that determine cell fate, patterning, and organogenesis. In the coordination of various developmental programs, several plant hormones play decisive roles, among which auxin is the best-documented hormonal signal. Despite the broad range of processes influenced by auxin, how such a single signaling molecule can be translated into a multitude of distinct responses remains unclear. In Arabidopsis thaliana, lateral root development is a classic example of a developmental process that is controlled by auxin at multiple stages. Therefore, we used lateral root formation as a model system to gain insight into the multifunctionality of auxin. We were able to demonstrate the complementary and sequential action of two discrete auxin response modules, the previously described Solitary Root/indole-3-Acetic Acid (IAA)14-Auxin Response Factor (ARF)7-ARF19-dependent lateral root initiation module and the successive Bodenlos/IAA12-Monopteros/ARF5-dependent module, both of which are required for proper organogenesis. The genetic framework in which two successive auxin response modules control early steps of a developmental process adds an extra dimension to the complexity of auxin's action.
Assuntos
Arabidopsis/efeitos dos fármacos , Ácidos Indolacéticos/farmacologia , Raízes de Plantas/efeitos dos fármacos , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Ciclinas/genética , Fatores de Transcrição E2F/genética , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Morfogênese , Reguladores de Crescimento de Plantas/farmacologia , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas , Proteínas Serina-Treonina Quinases , Receptores de Superfície Celular/genética , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
The Arabidopsis embryonic root meristem is initiated by the specification of a single cell, the hypophysis. This event critically requires the antagonistic auxin response regulators MONOPTEROS and BODENLOS, but their mechanism of action is unknown. We show that these proteins interact and transiently act in a small subdomain of the proembryo adjacent to the future hypophysis. Here they promote transport of auxin, which then elicits a second response in the hypophysis itself. Our results suggest that hypophysis specification is not the direct result of a primary auxin response but rather depends on cell-to-cell signaling triggered by auxin in adjacent cells.
Assuntos
Arabidopsis/embriologia , Arabidopsis/metabolismo , Ácidos Indolacéticos/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Transporte Biológico Ativo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Meristema/citologia , Meristema/embriologia , Meristema/metabolismo , Modelos Biológicos , Mutação , Raízes de Plantas/embriologia , Raízes de Plantas/metabolismo , Plantas Geneticamente Modificadas , Transdução de Sinais , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The plant hormone auxin has been implicated in virtually every aspect of plant growth and development. Auxin acts by promoting the degradation of transcriptional regulators called Aux/IAA proteins. Aux/IAA degradation requires TIR1, an F box protein that has been shown to function as an auxin receptor. However, loss of TIR1 has a modest effect on auxin response and plant development. Here we show that three additional F box proteins, called AFB1, 2, and 3, also regulate auxin response. Like TIR1, these proteins interact with the Aux/IAA proteins in an auxin-dependent manner. Plants that are deficient in all four proteins are auxin insensitive and exhibit a severe embryonic phenotype similar to the mp/arf5 and bdl/iaa12 mutants. Correspondingly, all TIR1/AFB proteins interact with BDL, and BDL is stabilized in triple mutant plants. Our results indicate that TIR1 and the AFB proteins collectively mediate auxin responses throughout plant development.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/embriologia , Proteínas F-Box/metabolismo , Ácidos Indolacéticos/metabolismo , Proteínas de Plantas/metabolismo , Receptores de Superfície Celular/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas F-Box/genética , Ácidos Indolacéticos/genética , Mutação , Plantas Geneticamente Modificadas , Receptores de Superfície Celular/genética , Transdução de Sinais , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The basic body plan of the adult plant is established during embryogenesis, resulting in the juvenile form of the seedling. Arabidopsis embryogenesis is distinguished by a highly regular pattern of cell divisions. Some of these divisions are asymmetric, generating daughter cells with different fates. However, their subsequent differentiation might still depend on cell-cell communication to be fully accomplished or maintained. In some cases, cell fate specification solely depends on cell-cell communication that in general plays an important role in the generation of positional information within the embryo. Although auxin-dependent signalling has received much attention, other ways of cell-cell communication have also been demonstrated or suggested. This review focuses on aspects of pattern formation and cell-cell communication during Arabidopsis embryogenesis up to the mid-globular stage of development.