RESUMO
The redox state of the photosynthetic electron transport chain acts as a critical sensing mechanism by regulating the transcription of key genes involved in the acclimation response to a change in the environment. In the present study we show that the small LuxR-type regulator PedR interacts with Trx (thioredoxin) to achieve photosynthetic electron-transport-dependent transcriptional regulation in the cyanobacterium Synechocystis sp. PCC 6803. TrxM, an isoform of Trx, was isolated as an interacting factor of PedR by pull-down assays. In vitro analysis revealed that the intermolecular disulfide bond formed between Cys80 residues of the PedR homodimer was reduced by both TrxM and TrxX. It has been shown previously that, although PedR is active under low-light conditions, it becomes transiently inactivated following a shift to high-light conditions, with a concomitant conformational change [Nakamura and Hihara (2006) J. Biol. Chem. 281, 36758-36766]. In the present study, we found that the conformational change of PedR and the change in the transcript level of its target gene were minimal when mutants of Synechocystis that lack ferredoxin-Trx reductase or NADPH-Trx reductase were exposed to high levels of light. These results indicate that the reduction of PedR by Trx causes transient inactivation of PedR upon the shift of cyanobacterial cells to high-light conditions.
Assuntos
Proteínas de Bactérias/metabolismo , Cianobactérias/genética , Regulação Bacteriana da Expressão Gênica , Proteínas Repressoras/metabolismo , Tiorredoxinas/metabolismo , Transativadores/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Cianobactérias/metabolismo , Oxirredução , Fotossíntese/genética , Proteínas Repressoras/química , Synechocystis/genética , Synechocystis/metabolismo , Tiorredoxinas/química , Transativadores/química , Transcrição GênicaRESUMO
Plant growth and development are sustained by meristems. Meristem activity is controlled by auxin and cytokinin, two hormones whose interactions in determining a specific developmental output are still poorly understood. By means of a comprehensive genetic and molecular analysis in Arabidopsis, we show that a primary cytokinin-response transcription factor, ARR1, activates the gene SHY2/IAA3 (SHY2), a repressor of auxin signaling that negatively regulates the PIN auxin transport facilitator genes: thereby, cytokinin causes auxin redistribution, prompting cell differentiation. Conversely, auxin mediates degradation of the SHY2 protein, sustaining PIN activities and cell division. Thus, the cell differentiation and division balance necessary for controlling root meristem size and root growth is the result of the interaction between cytokinin and auxin through a simple regulatory circuit converging on the SHY2 gene.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Arabidopsis/citologia , Citocininas/metabolismo , Proteínas de Ligação a DNA/metabolismo , Ácidos Indolacéticos/metabolismo , Meristema/citologia , Proteínas Nucleares/genética , Raízes de Plantas/citologia , Fatores de Transcrição/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Diferenciação Celular , Divisão Celular , Citocininas/genética , Proteínas de Ligação a DNA/genética , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Proteínas de Membrana Transportadoras/genética , Proteínas de Membrana Transportadoras/metabolismo , Meristema/crescimento & desenvolvimento , Proteínas Nucleares/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Regiões Promotoras Genéticas , Transdução de Sinais , Fatores de Transcrição/genéticaRESUMO
The expression of many cyanobacterial genes is regulated by the redox state of the photosynthetic electron transport chain. However, factors involved in this regulation have not been identified. In this study, we demonstrate that a small LuxR-type regulator in Synechocystis sp. PCC 6803, PedR (Ssl0564), senses the activity of photosynthetic electron transport to achieve the photon flux density-dependent transcriptional regulation. PedR is constitutively expressed in Synechocystis cells and exists as a dimer bridged by intermolecular disulfide bond(s). It activates the expression of chlL, chlN, chlB, and slr1957 and represses that of ndhD2, rpe, and the pedR (ssl0564)-sll0296 operon under conditions where the activity of photosynthetic electron transport is low. When the supply of reducing equivalents from photosynthetic electron transport chain increases upon the elevation of photon flux density, PedR is inactivated through its conformational change within 5 min. This mechanism enables transient induction or repression of the target genes in response to sudden changes in light environment. The fact that orthologs of PedR are conserved among all the cyanobacterial genomes sequenced so far indicates that this type of transcriptional regulation is essential for cyanobacteria to acclimate to changing environments.
Assuntos
Regulação da Expressão Gênica , Proteínas Repressoras/genética , Proteínas Repressoras/fisiologia , Synechocystis/química , Transativadores/genética , Transativadores/fisiologia , Sequência de Aminoácidos , Dissulfetos/química , Transporte de Elétrons , Glucose/química , Dados de Sequência Molecular , Análise de Sequência com Séries de Oligonucleotídeos , Oxirredução , Fótons , Fotossíntese , Filogenia , RNA/química , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência de AminoácidosRESUMO
Pirin is a recently identified protein in eukaryotes as a transcription cofactor or as an apoptosis-related protein. Although Pirin is highly conserved from bacteria to human, there have been no reports on prokaryotic Pirin orthologs. We show here that pirA (sll1773) encoding an ortholog of Pirin together with an adjacent gene, pirB (ssl3389), was upregulated under high salinity and some other stress conditions in a cyanobacterium Synechocystis sp. PCC 6803. Induction of the pirAB genes was not related to cell death and disruption of pirA did not affect the gene expression profile. Expression of the pirAB genes was negatively regulated by a LysR family transcriptional regulator encoded by pirR (slr1871) located immediately upstream of pirAB in the divergent direction. DNA microarray analysis indicated that PirR repressed expression of closely located ORFs, slr1870 and mutS (sll1772), in addition to pirAB and pirR itself.
