RESUMO
Expression of the gene encoding the beta subunit of beta-conglycinin, a major soybean seed storage protein, is upregulated by sulfur deficiency and downregulated by methionine (Met). The tissue-specificity of these regulatory mechanisms was studied using a sulfate-responsive region (beta(SR)) from the beta subunit gene promoter. Transgenic Arabidopsis thaliana lines were generated carrying a green fluorescent protein (GFP) reporter gene under control of the cauliflower mosaic virus 35S RNA promoter with a tandem repeat of the beta(SR) element, referred to as the P35S::beta(SR)x3: GFP transgene. Upregulation of P35S::beta(SR)x3:GFP by sulfur deficiency was strongest in leaf margins, where symptoms of sulfur deficiency first appear. P35S::beta(SR)x3:GFP was also upregulated at 2 d after a medium shift from sulfur-sufficient to sulfur-deficient conditions, suggesting that the chimeric promoter is an efficient indicator of sulfur nutritional status. Analysis of transgene expression in a Met-overaccumulating mto1-1 mutation background revealed that the beta(SR) region carries sufficient information for downregulation of promoter activity by Met in developing seeds, but not in young rosettes. Comparisons with another transgenic line, in which the full-length beta promoter is active in non-seed tissues, also suggested that at least two separate tissue-specific mechanisms exist for the downregulation of the beta promoter by Met.
Assuntos
Arabidopsis/genética , Globulinas/genética , Metionina/farmacologia , Regiões Promotoras Genéticas/genética , Proteínas de Soja/genética , Sulfatos/farmacologia , Antígenos de Plantas , Caulimovirus/genética , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes Reporter/efeitos dos fármacos , Genes Reporter/genética , Globulinas/efeitos dos fármacos , Proteínas de Fluorescência Verde , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Mutação , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas/efeitos dos fármacos , Sequências Reguladoras de Ácido Nucleico/genética , Proteínas de Armazenamento de Sementes , Sementes/efeitos dos fármacos , Sementes/genética , Proteínas de Soja/efeitos dos fármacos , Glycine max/efeitos dos fármacos , Glycine max/genética , Especificidade por SubstratoRESUMO
Effects of plant hormones on a sulfur-deficiency responsive element (betaSR) from the promoter region of the beta subunit gene of beta-conglycinin, a major seed storage protein of soybean, were investigated using transgenic Arabidopsis thaliana. Among the hormones tested, the cytokinins, trans-zeatin (Z) and trans-zeatin riboside, upregulated gene expression directed by the betaSR element both in the presence and in the absence of sulfate in the medium. Z also increased transcript accumulation of two endogenous sulfur-responsive genes, the adenosine 5'-phosphosulfate reductase (APR1) and the Sultr2;2, a sulfate transporter. Concentrations of cytokinins were unaltered during early stages of sulfur starvation when expression of these genes was upregulated. Z did not alter concentrations of O-acetyl-L-serine, a positive regulator of gene expression in sulfur starvation response. Concentrations of sucrose, which is known to upregulate expression of APR1, were increased in rosette leaves by Z. Sucrose application to the medium also increased expression directed by the betaSR element, although sucrose concentrations in tissues were not significantly altered by sulfur availability. These results suggest that exogenously applied cytokinins positively regulate expression of these sulfur responsive genes through a pathway independent of that from sulfur starvation, possibly through increasing sucrose concentrations in tissues.
