RESUMO
The plant hormone gibberellin (GA) is known to modulate various aspects of plant cell differentiation and development. The current model of GA-mediated regulation is based on a de-repressible system and includes specific protein modification and degradation. HRT, a zinc finger protein from barley has been shown to have GA-dependent transcriptional repressing activity on the seed-specific alpha-amylase promoter [Raventos, D., Skriver, K., Schlein, M., Karnahl, K., Rogers, S.W., Rogers, J.C. and Mundy, J. 1998. J. Biol. Chem. 273: 23313-23320]. Here we report the characterization of a dicot homologue from Brassica napus (BnET) and provide evidence for its role in GA response modulation suggesting that this could be a conserved feature of this gene family. When BnET is ectopically expressed in either Arabidopsis or tobacco the phenotypes include dwarfism due to shorter internodes and late flowering, reduced germination rate, increased anthocyanin content and reduced xylem lignification as a marker for terminal cell differentiation. Transient expression in protoplasts supports the notion that this most likely is due to a transcriptional repression of GA controlled genes. Finally, histological analysis showed that in contrast to other GA deficient mutants the shorter internodes were due to fewer but not smaller cells, suggesting a function of BnET in GA-mediated cell division control.
Assuntos
Arabidopsis/efeitos dos fármacos , Arabidopsis/crescimento & desenvolvimento , Brassica napus/genética , Giberelinas/farmacologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Sequência de Aminoácidos , Antocianinas/biossíntese , Antocianinas/metabolismo , Arabidopsis/citologia , Arabidopsis/genética , Núcleo Celular/metabolismo , Clonagem Molecular , Citocininas/farmacologia , DNA Complementar/genética , DNA Complementar/isolamento & purificação , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Germinação , Ácidos Indolacéticos/farmacologia , Lignina/metabolismo , Dados de Sequência Molecular , Caules de Planta/citologia , Caules de Planta/genética , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas/genética , Estrutura Terciária de Proteína , Homologia de Sequência de Aminoácidos , Nicotiana/citologia , Nicotiana/efeitos dos fármacos , Nicotiana/genética , Nicotiana/crescimento & desenvolvimento , Zinco/metabolismoRESUMO
The Arabidopsis mutants fus3 and abi3 show pleiotropic effects during embryogenesis including reduced levels of transcripts encoding embryo-specific seed proteins. To investigate the interaction between the B3-domain-containing transcription factors FUS3 and ABI3 with the RY cis-motif, conserved in many seed-specific promoters, a promoter analysis as well as band-shift experiments were performed. The analysis of promoter mutants revealed the structural requirements for the function of the RY cis-element. It is shown that both the nucleotide sequence and the alternation of purin and pyrimidin nucleotides (RY character) are essential for the activity of the motif. Further, it was shown that FUS3 and ABI3 can act independently of each other in controlling promoter activity and that the RY cis-motif is a target for both transcription factors. For FUS3, which is so far the smallest known member of the B3-domain family, a physical interaction with the RY motif was established. The functional and biochemical data demonstrate that the regulators FUS3 and ABI3 are essential components of a regulatory network acting in concert through the RY-promoter element to control gene expression during late embryogenesis and seed development.
