RESUMO
The Arabidopsis thaliana response regulator 4, expressed in response to phytochrome B action, specifically interacts with the extreme amino-terminus of the photoreceptor. The response regulator 4 stabilizes the active Pfr form of phytochrome B in yeast and in planta, thus elevates the level of the active photoreceptor in vivo. Accordingly, transgenic Arabidopsis plants overexpressing the response regulator 4 display hypersensitivity to red light but not to light of other wavelengths. We propose that the response regulator 4 acts as an output element of a two-component system that modulates red light signaling on the level of the phytochrome B photoreceptor.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Luz , Células Fotorreceptoras , Fitocromo/metabolismo , Transdução de Sinais , Fatores de Transcrição , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Núcleo Celular/metabolismo , Citoplasma/metabolismo , Escuridão , Genes de Plantas , Fenótipo , Fosforilação , Fitocromo/química , Fitocromo B , Plantas Geneticamente Modificadas , Conformação Proteica , Proteínas Recombinantes de Fusão/metabolismo , Técnicas do Sistema de Duplo-Híbrido , Leveduras/genética , Leveduras/metabolismoRESUMO
Two-component signal systems regulate a variety of cellular activities. They involve at least two common signalling molecules: a signal-sensing kinase and a response regulator that mediates the output response. Multistep systems also require proteins containing phosphotransfer domains. Here we report that the response regulator ARR2 from Arabidopsis is predominantly expressed in pollen and is localized in the nuclear compartment of the plant cell. Furthermore, ARR2 is transcriptionally active in yeast and binds to the promoters of nuclear genes for several components of mitochondrial respiratory chain complex I (nCI) from Arabidopsis. The nuclear nCI genes are up-regulated in pollen during spermatogenesis. The transcription factor functions of ARR2 are mediated by its C-terminal output domain. Our data identify ARR2 as the first eukaryotic response regulator which functions as a transcription factor at a known promoter sequence. Yeast two-hybrid analysis and in vitro interaction studies suggest that ARR2 very probably forms part of a multistep two-component signalling mechanism that includes HPt proteins like AHP1 or AHP2. These findings point to an as yet unidentified signal transduction system that may regulate aspects of floral and mitochondrial gene expression.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/genética , Núcleo Celular/genética , Proteínas de Ligação a DNA/genética , Regulação da Expressão Gênica de Plantas , Mitocôndrias/genética , NADH NADPH Oxirredutases/genética , Fosfotransferases , Fatores de Transcrição/genética , Arabidopsis/metabolismo , Arabidopsis/ultraestrutura , Núcleo Celular/metabolismo , Proteínas de Ligação a DNA/metabolismo , Complexo I de Transporte de Elétrons , Mitocôndrias/metabolismo , Dados de Sequência Molecular , NADH NADPH Oxirredutases/metabolismo , Fosfotransferases (Aceptor do Grupo Álcool)/genética , Fosfotransferases (Aceptor do Grupo Álcool)/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Pólen/genética , Pólen/metabolismo , Regiões Promotoras Genéticas , Estrutura Terciária de Proteína , Transdução de Sinais , Fatores de Transcrição/metabolismo , Técnicas do Sistema de Duplo-HíbridoRESUMO
To study negative interactions between phytochromes, phytochrome B (phyB) overexpressor lines, the mutants phyA-201, phyB-4, phyB-5, phyD-1, phyA-201 phyB-5, phyA-201 phyD-1, and phyB-5 phyD-1 of Arabidopsis were used. Endogenous phyB, but not phytochrome D (phyD), partly suppressed phytochrome A (phyA)-dependent inhibition of hypocotyl elongation in far-red light (FR). Dichromatic irradiation demonstrated that the negative effect of phyB was largely independent of the photoequilibrium, i.e. far-red light absorbing form of phytochrome formation. Moreover, phyB-4, a mutant impaired in signal transduction, did not show a loss of inhibition of phyA by phyB. Overexpression of phyB, conversely, resulted in an enhanced inhibition of phyA function, even in the absence of supplementary carbohydrates. However, overexpression of a mutated phyB, which cannot incorporate the chromophore, had no detectable effect on phyA action. In addition to seedling growth, accumulation of anthocyanins in FR, another manifestation of the high irradiance response, was strongly influenced by phyB holoprotein. Induction of seed germination by FR, a very low fluence response, was suppressed by both endogenous phyB and phyD. In conclusion, we show that both classical response modes of phyA, high irradiance response, and very low fluence response are subject to an inhibitory action of phyB-like phytochromes. Possible mechanisms of the negative interference are discussed.
Assuntos
Arabidopsis/fisiologia , Células Fotorreceptoras , Fitocromo/farmacologia , Fitocromo/fisiologia , Fatores de Transcrição , Antocianinas/metabolismo , Arabidopsis/efeitos dos fármacos , Proteínas de Arabidopsis , Germinação/efeitos dos fármacos , Hipocótilo/efeitos dos fármacos , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/efeitos da radiação , Fitocromo A , Fitocromo BRESUMO
Blue light responses in higher plants can be mediated not only by specific blue light receptors, but also by the red/far-red photoreversible phytochrome system. The question of interdependence between these photoreceptors has been debated over many years. The availability of Arabidopsis mutants for the blue light receptor CRY1 and for the two major phytochromes phyA and phyB allows a reinvestigation of this question. The analysis of photocontrol of seed germination, inhibition of hypocotyl growth and anthocyanin accumulation clearly demonstrates that (i) phyA shows a strong control in blue light responses especially at low fluence rates; (ii) phyB mediated induction reactions can be reversed by subsequent blue light irradiations; and (iii) CRY1 mediates blue light controlled inhibition of hypocotyl growth only at fluence rates higher than 5 mumol m-2s-1 and independently of phytochrome A and B.
