RESUMO
Plants both produce and utilize carbohydrates and have developed mechanisms to regulate their sugar status and co-ordinate carbohydrate partitioning. High sugar levels result in a feedback inhibition of photosynthesis and an induction of storage processes. We used a genetic approach to isolate components of the signalling pathway regulating the induction of starch biosynthesis. The regulatory sequences of the sugar inducible ADP-glucose pyrophosphorylase subunit ApL3 were fused to a negative selection marker. Of the four impaired sucrose induction (isi) mutants described here, two (isi1 and isi2) were specific to this screen. The other two mutants (isi3 and isi4) showed additional phenotypes associated with sugar-sensing screens that select for seedling establishment on high-sugar media. The isi3 and isi4 mutants were found to be involved in the abscisic acid signalling pathway. isi3 is allelic to abscisic acid insensitive4 (abi4), a gene encoding an Apetala2-type transcription factor; isi4 was found to be allelic to glucose insensitive1 (gin1) previously reported to reveal cross-talk between ethylene and glucose signalling. Here we present an alternative interpretation of gin1 as an allele of the ABA-deficient mutant aba2. Expression analysis showed that ABA is unable to induce ApL3 gene expression by itself, but greatly enhances ApL3 induction by sugar. Our data suggest a major role for ABA in relation to sugar-signalling pathways, in that it enhances the ability of tissues to respond to subsequent sugar signals.
Assuntos
Ácido Abscísico/metabolismo , Arabidopsis/genética , Amido/biossíntese , Sacarose/farmacologia , Alelos , Arabidopsis/efeitos dos fármacos , Proteínas de Arabidopsis , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Teste de Complementação Genética , Glucose-1-Fosfato Adenililtransferase , Modelos Biológicos , Mutação , Nucleotidiltransferases/genética , Folhas de Planta/efeitos dos fármacos , Transdução de Sinais/genética , Distribuição TecidualRESUMO
The expression of many genes encoding transcriptional activators in prokaryotes and eukaryotes is upregulated through positive feedback activation. During positive feedback activation, a transcriptional activator binds to its own promoter and thus increases its own expression as well as the expression of its target genes. In the simplest case, increased levels of the transcriptional activator can be directly correlated with increased expression of its target genes. In this study, we present a gene expression system, designated feedforward loop (FFL) system, which makes use of this kind of positive feedback regulation for the expression of plant transgenes. We show in transient and stable transformation experiments that such a system is functional and that it can be used to obtain high level gene expression in plants. We also provide evidence that the transgene is ubiquitously expressed when using the FFL system. Finally, we discuss the possibilities of using FFL gene expression systems for applications in plant molecular genetics and biotechnology.
Assuntos
Marcação de Genes/métodos , Genes de Plantas , Ativação Transcricional , Agrobacterium tumefaciens/genética , Arabidopsis/genética , Arabidopsis/metabolismo , Aspergillus nidulans/genética , Retroalimentação Fisiológica , Expressão Gênica , Regulação da Expressão Gênica de Plantas , Modelos Genéticos , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas , Análise de Sequência de DNA , Nicotiana/genética , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Transcrição Gênica , Transformação Genética , Regulação para Cima/genéticaRESUMO
Storage protein gene expression has been studied in relation to mitotic activity to ascertain whether these processes are linked during embryo development in pea. Sections from immature pea embryos were probed by in situ hybridisation to show the pattern of vicilin storage protein gene expression. In addition, the location of mitotic cells was identified using fluorescence microscopy. Vicilin mRNA was first localised in the parenchyma cells of the upper adaxial region of the cotyledons. As the embryos increased in fresh weight, gene expression spread from this region, in a wave-like manner, down and across the cotyledons. The gene was only expressed in those regions of the embryo that lacked mitotic activity.
