RESUMO
Light-dependent transcription factors GLKs of Arabidopsis thaliana are involved in the anterograde regulation of chloroplast biogenesis during deetiolation: they regulate the expression of photosynthetic nuclear-encoded genes and also mediate the transcription of plastid genes. Chloroplast biogenesis is determined at the same time by light and by endogenous factors (phytohormones), among which cytokinins significantly accelerate the formation of photosynthetically active chloroplasts. In this work, it was shown that trans-factors GLKs function as cytokinin-dependent regulators, mediating the positive cytokinin effect on the plastome expression through the activation of transcription of the SCA3 nuclear gene encoding the plastid RNA polymerase RPOTp.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Citocininas/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Estiolamento , Regulação da Expressão Gênica de Plantas , Folhas de Planta/metabolismo , Plastídeos/genética , Cloroplastos/genética , Cloroplastos/metabolismo , RNA Polimerases Dirigidas por DNA/genética , Expressão GênicaRESUMO
Melatonin is a signaling molecule that mediates multiple stress-dependent reactions. Under photooxidative stress conditions generating intensive ROS production, exogenous melatonin (50 µM) contributed to maintaining the expression of mitochondrial encoded genes and up-regulation of RNA-polymerase genes RPOTm and RPOTmp, operating through the CAND2 receptor and α-subunit of the heterotrimeric G protein GPA1 coupled with CAND2. Unlike wild-type plants, mutants with defective CAND2 and GPA1 genes exhibited no decrease in the alternative pathway of leaf respiration, as well as the activity of an alternative oxidase, and the expression of the AOX1a gene. At the same time, the protective effect of exogenous melatonin on some physiological indicators did not depend on the receptor and was associated with the direct antioxidant function of the regulator. Thus, melatonin under photooxidative stress conditions can act as an antioxidant and as a hormone capable of regulating the expression of nuclear and organelle genes through the components of melatonin signal perception.
Assuntos
Proteínas de Arabidopsis , Regulação da Expressão Gênica de Plantas , Genes Mitocondriais , Melatonina , Receptores Acoplados a Proteínas G , Arabidopsis , Proteínas de Arabidopsis/genética , Expressão Gênica , Melatonina/metabolismo , Melatonina/farmacologia , Receptores Acoplados a Proteínas G/genética , Receptores de Melatonina/metabolismoRESUMO
The expression profiles of the PAP genes, encoding proteins associated with plastid multisubunit RNA polymerase, were studied in dry seeds, during germination, and at the early stages of Arabidopsis thaliana seedling formation. A detailed analysis of the PAP transcript levels by RT-PCR showed that the transition of seeds from dormancy to active growth is accompanied by a drastic increase in the transcript accumulation of all studied genes on the first day of germination, both in the light and in the dark. Further changes in transcript levels differed among PAP genes and were apparently determined by their functional specificity. It was established for the first time that the expression of individual PAP genes is regulated by circadian rhythms, in addition to factors of ontogenetic and light nature.
Assuntos
ArabidopsisRESUMO
The physiological and molecular responses of Arabidopsis thaliana plants to cold stress were studied. Exposure to a low non-freezing temperature (4°C, 5 days) caused a decrease in the physiological functions and activity of a number of photosynthetic genes and elevation in expression of the cold stress gene COR15a, the product of which protects chloroplasts. It was shown for the first time that in parallel to a general inhibition of physiological functions under hypothermia, an increase in the expression of most genes for the chloroplast transcription apparatus was observed. This is obviously one of the compensatory mechanisms of adaptation aimed to maintain cellular homeostasis and physiological functions under hypothermia.
Assuntos
Arabidopsis/genética , Arabidopsis/metabolismo , Cloroplastos/genética , Cloroplastos/metabolismo , Resposta ao Choque Frio/genética , Regulação da Expressão Gênica de Plantas , Fotossíntese/genética , Adaptação Fisiológica , Proteínas de Arabidopsis/biossíntese , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Temperatura Baixa/efeitos adversosRESUMO
HY5 (ELONGATED HYPOCOTYL5), a bZIP transcription factor, is one of the main regulators of light and hormonal signaling. Among the targets of this gene, the genes for the transcriptional complex of chloroplasts whose coordinated expression ensures the initial stages of photomorphogenesis are particularly significant. In this study, we showed that, during de-etiolation, HY5 functions as a positive CK-dependent regulator of the expression of genes encoding proteins associated with plastid RNA polymerase (PAP), which functions below the primary chain of sensing the cytokinin signal. The absence of blocking effect of mutations of the CRY1, CRY2, PHYA, and PHYB photoreceptor genes on the CK-dependent content of PAP gene transcripts indicates the parallel action of the hormone and light in their regulation.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/metabolismo , Bactérias/enzimologia , Fatores de Transcrição de Zíper de Leucina Básica/genética , Citocininas/metabolismo , RNA Polimerases Dirigidas por DNA/genética , Estiolamento , Plastídeos/enzimologia , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/metabolismo , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Cloroplastos/metabolismo , Citocininas/genética , Regulação da Expressão Gênica de Plantas , Transdução de SinaisRESUMO
The treatment of Arabidopsis thaliana plants with exogenous cytokinin (CK) followed by heat shock (HS) activated the expression of the genes for the plastid transcription machinery but adversely affected the plant viability. Abscisic acid (ABA), conversely, promoted maintaining the resistance to HS and had differentially affected different components of the plastid transcriptional complex. This hormone suppressed the accumulation of transcripts of PEP genes and the genes encoding PAP proteins, which are involved in DNA-RNA metabolism. However, it had no effect or activated the expression of NEP genes and PAP genes, which are involved in the redox regulation, as well as the genes encoding the stress-inducible trans-factor (SIG5) and the plastid transcription Ser/Thr protein kinase (cpCK2). Thus, for the adaptation of plants to elevated temperatures, both increase and decrease in the expression of the genes for the plastid transcriptional machinery with the involvement of various regulatory systems, including phytohormones, are equally significant.
Assuntos
Ácido Abscísico/farmacologia , Arabidopsis/efeitos dos fármacos , Citocininas/farmacologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Resposta ao Choque Térmico/genética , Plastídeos/genética , Transcrição Gênica/efeitos dos fármacos , Arabidopsis/citologia , Arabidopsis/genética , Arabidopsis/fisiologia , Resposta ao Choque Térmico/efeitos dos fármacos , Plastídeos/efeitos dos fármacosRESUMO
As multifunctional regulators of physiological processes, phytohormones play an important role in the regulation of expression of the plastid genome and chloroplast biogenesis. Hormones can directly regulate the expression of genes localized in the chloroplast genome. However, many components of the plastid transcription apparatus are encoded by nuclear rather than plastid genes. It remains obscure whether these nuclear genes are subject to hormonal regulation. This is the first study to show that phytohormones exert differential effects on the expression of nuclear genes of the transcription machinery of the Arabidopsis thaliana plastome. RT-PCR analysis showed that the level of transcripts of the majority of studied genes was activated by trans-zeatin but decreased under the influence of ABA, methyl jasmonate, and salicylic acid, whereas ethylene had no significant effect, and the effects of brassinolide depended on the illumination conditions. The results of this study indicate that the hormonal regulation of the plastome expression can be mediated by differential regulation of the nuclear genes encoding plastid transcription machinery components.
Assuntos
Arabidopsis/citologia , Arabidopsis/genética , Núcleo Celular/efeitos dos fármacos , Regulação da Expressão Gênica em Archaea/efeitos dos fármacos , Reguladores de Crescimento de Plantas/farmacologia , Plastídeos/efeitos dos fármacos , Transcrição Gênica/efeitos dos fármacos , Arabidopsis/efeitos dos fármacos , Núcleo Celular/genética , Plastídeos/genética , Fatores de TempoRESUMO
Analysis by real-time PCR of single and double insertion mutants of A. thaliana with inactivated cytokinin receptor genes showed that the level of transcripts of some of plastid genes during skotomorphogenesis depended on the state of functionally active receptor AHK3. The cytokinin-regulated plastid encoded genes involved the housekeeping genes (rpoB and accD) and the genes for photosynthetic proteins (ndhA, psbA, atpB, and psaA). However, the absence of hormone activation of plastid encoded genes engaged in the translation of plastid proteins, rRNA (rrn16), and tRNA (trnE), indirectly indicate the disruption of the synthesis of chloroplast proteins in the dark.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/genética , Escuridão , Regulação da Expressão Gênica de Plantas/fisiologia , Genomas de Plastídeos , Histidina Quinase/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Citocininas/metabolismo , Técnicas de Inativação de Genes , Genomas de Plastídeos/fisiologia , Histidina Quinase/genética , Mutagênese Insercional , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/metabolismo , Fatores de Transcrição/metabolismoAssuntos
Hordeum/genética , Ácidos Fosfínicos/farmacologia , Plastídeos/metabolismo , RNA Polimerase I/metabolismo , Triazinas/farmacologia , Clorofila/metabolismo , Cloroplastos/metabolismo , Cromatina/metabolismo , Citocininas/metabolismo , DNA/metabolismo , Hordeum/efeitos dos fármacos , Hordeum/metabolismo , Peptídeos/química , Ácidos Fosfínicos/química , Fotossíntese , Folhas de Planta/metabolismo , RNA/metabolismo , Sementes/metabolismo , Fatores de Tempo , Triazinas/químicaAssuntos
Metais Pesados/farmacologia , Plastídeos/efeitos dos fármacos , Plastídeos/genética , Splicing de RNA/efeitos dos fármacos , Splicing de RNA/genética , Transcrição Gênica/efeitos dos fármacos , Transcrição Gênica/genética , Hordeum/efeitos dos fármacos , Hordeum/crescimento & desenvolvimento , Plântula/efeitos dos fármacos , Plântula/crescimento & desenvolvimentoAssuntos
Cloroplastos/genética , Citocininas/metabolismo , Regulação da Expressão Gênica de Plantas , Hordeum/metabolismo , Folhas de Planta/metabolismo , Transcrição Gênica , Escuridão , Luz , Substâncias Macromoleculares , Fotossíntese , RNA/metabolismo , Temperatura , Fatores de Tempo , Uridina TrifosfatoAssuntos
Citocininas/farmacologia , Regulação da Expressão Gênica de Plantas , Genes de RNAr , Hordeum/genética , Citocininas/fisiologia , Regulação da Expressão Gênica , Hordeum/crescimento & desenvolvimento , Folhas de Planta/genética , Folhas de Planta/crescimento & desenvolvimento , RNA Ribossômico/biossíntese , RNA Ribossômico/genética , Transcrição GênicaRESUMO
A functionally important region in the promoter of the spinach photosynthesis gene AtpC, which encodes the subunit gamma of the chloroplast ATP synthase, is located immediately upstream of the CAAT-box. A single nucleotide exchange in this region (AAAATTCAAT --> AAGATCAAT) uncouples the expression of an AtpC promoter::uidA gene fusion from the regulation by light, cytokinin, and functional plastids and results in a high constitutive expression of the reporter gene. By screening an Arabidopsis thaliana expression library with a double-stranded wild-type oligonucleotide from this promoter region, we have isolated cDNAs from Arabidopsis libraries that code for plant homologs of the CAAT-box binding factor (CBF)-C. Binding occurs only in the presence of nuclear extracts, consistent with reports from metazoa CBFs that the subunits A and B in addition to C are required for the formation of the CBF-DNA complex. At least eight genes with homologies to CBF-C are present in the Arabidopsis genome; one of them exhibits striking similarities to the gene for the human global transcriptional repressor Drap1. In gel mobility shift assays, low binding activity of CBF to the wild-type AtpC promoter sequence was observed with nuclear extracts from tissue with low AtpC expression levels, i.e. extracts from etiolated and photobleached seedlings, whereas high binding activity was detectable with extracts from tissues with high AtpC expression levels, i.e. extracts from light-grown seedlings and etiolated seedlings treated with cytokinin. Binding to the mutant sequence, which directs constitutive high level uidA expression in vivo, is significantly stronger than to the wild-type sequence. The data are consistent with the idea that the assembly of CBF at the AtpC promoter is regulated in response to light and cytokinin and that the low level of expression in etiolated and photobleached material is caused by an inhibitory effect. The structure/function relationships of the Arabidopsis CBFs are discussed in relation to their regulatory function in AtpC gene expression.
Assuntos
Arabidopsis/genética , Citocininas/metabolismo , Proteínas de Ligação a DNA/genética , Fotossíntese/genética , Plastídeos/fisiologia , Regiões Promotoras Genéticas , ATPases Translocadoras de Prótons/genética , Spinacia oleracea/genética , Sequência de Aminoácidos , Arabidopsis/metabolismo , Aspergillus/genética , Proteínas Estimuladoras de Ligação a CCAAT , Cloroplastos/genética , Cloroplastos/metabolismo , DNA Complementar , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/metabolismo , Escuridão , Genes Reporter , Genoma de Planta , Humanos , Luz , Dados de Sequência Molecular , Plantas Geneticamente Modificadas , Plantas Tóxicas , Plastídeos/genética , Saccharomyces cerevisiae/genética , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Spinacia oleracea/metabolismo , Nicotiana , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Plastid biogenesis in etiolated lupine (Lupinus luteus L.) cotyledons is highly sensitive to cytokinins and abscisic acid. In the presence of the synthetic cytokinin N6-benzylaminopurine, greening and plastid biogenesis is substantially promoted as compared to untreated controls, whereas abscisic acid has an inhibitory effect. Faster greening in cytokinin-treated cotyledons is accompanied by a higher level and slower degradation of the light-sensitive protochlorophyllide-oxidoreductase (POR); while ABA has the opposite effect. The phytohormones appear to modulate POR gene expression, since the steady-state levels of POR mRNA, as well as transcripts of other nuclear genes for plastid proteins, are strongly increased by cytokinin and reduced by abscisic acid treatment. When etiolated lupine cotyledons were illuminated with far-red light prior to phytohormone application, the POR level substantially decreased; this was accompanied by the loss of the phytohormone's effect on greening. Based on these findings it is concluded that the level of POR and the integrity of the prolamellar body is crucial for cytokinin- and abscisic acid-controlled greening following transfer of etiolated lupine cotyledons into the light.
Assuntos
Ácido Abscísico/farmacologia , Clorofila/antagonistas & inibidores , Clorofila/biossíntese , Cotilédone/enzimologia , Citocininas/farmacologia , Oxirredutases atuantes sobre Doadores de Grupo CH-CH , Oxirredutases/biossíntese , Clorofila/efeitos da radiação , Cotilédone/efeitos dos fármacos , Cotilédone/efeitos da radiação , Luz , Oxirredutases/efeitos dos fármacos , Oxirredutases/efeitos da radiação , Plastídeos/efeitos dos fármacos , Plastídeos/enzimologia , Plastídeos/efeitos da radiação , RosalesRESUMO
Nuclear-encoded genes for proteins of the photosynthetic machinery represent a particular subset of genes. Their expression is cooperatively stimulated by discrete factors including the developmental stage of plastids and light. We have analyzed in transgenic tobacco the plastid- and light-dependent expression of a series of 5' promoter deletions of various nuclear genes from spinach, of fusions of defined promoter segments with the 90-bp 35S RNA CaMV minimal promoter, as well as with mutations in sequences with homologies to characterized cis-elements, to address the question of whether the plastid signal and light operate via the same or different cis-acting elements. In none of the 160 different transgenic lines (representing 32 promoter constructs from seven genes) analyzed, could significant differences be identified in the responses to the two regulatory pathways. The data are compatible with the idea that both signals control the expression of nuclear genes for plastid proteins via the same cis-acting elements.
Assuntos
Regulação da Expressão Gênica de Plantas , Nicotiana/genética , Plantas Tóxicas , Plastídeos/genética , Regiões Promotoras Genéticas , Transdução de Sinais/genética , Spinacia oleracea/genética , Luz , Mutagênese Sítio-Dirigida , Sondas de Oligonucleotídeos , Complexo de Proteínas do Centro de Reação Fotossintética/genética , Plantas Geneticamente Modificadas , Plastídeos/metabolismo , Spinacia oleracea/metabolismo , Nicotiana/metabolismoRESUMO
Run-on assays with isolated nuclei demonstrate that the transcription rates of AtpC and AtpD (gene products: the CF1 subunits gamma and delta of the chloroplast ATP synthase) are comparable in spinach seedlings. However, chimeric GUS gene fusions with 5'-flanking regions of the AtpC gene direct an approximately 10-fold lower GUS level in transgenic tobacco compared with equivalent fragments from the AtpD gene. Both promoters contain sequences in the vicinity of the respective TATA boxes, which are sufficient to direct light-regulated, plastid-dependent and organ-specific expression of the GUS gene. In contrast, the upstream regions of both promoters differ the higher GUS level directed by the AtpD promoter is caused by enhancer-like elements located upstream of the region involved in the regulated expression, while nucleotides upstream of -73 in the AtpC promoter contribute relatively little to the promoter activity. 5'-Deletion analyses and site-directed mutagenesis studies indicated that the -73/-48 bp AtpC region contains cis-elements crucial for this regulated expression. If five nucleotides within this region (-59/-55) are exchanged, the GUS gene is constitutively expressed and the activity in etiolated seedlings, in seedlings with photobleached plastids and in roots increases to the level detectable in green cotyledons. It is concluded that signal transduction pathways from different regulators converge prior to gene regulation and that these five nucleotides are part of a cis-element which functions as a repressor in darkness, in tissues with impaired plastids and in roots.
Assuntos
Regulação da Expressão Gênica de Plantas , Plastídeos/metabolismo , ATPases Translocadoras de Prótons/genética , Transcrição Gênica/efeitos da radiação , Sequência de Bases , Núcleo Celular/metabolismo , Cotilédone/metabolismo , Escuridão , Glucuronidase/biossíntese , Glucuronidase/genética , Luz , Dados de Sequência Molecular , Folhas de Planta/metabolismo , Raízes de Plantas/metabolismo , Plantas Geneticamente Modificadas , Plantas Tóxicas , Regiões Promotoras Genéticas , Proteínas Recombinantes de Fusão/biossíntese , Spinacia oleracea/genética , Distribuição Tecidual , Nicotiana/genéticaRESUMO
The levels of plastid gene transcripts are shown to be controlled by temperature in isolated pumpkin cotyledons. The temperature at which maximum transcript accumulation occurs varies between 38 and 42 degrees C for the genes studied (rbcL, psaA, psbA, psbB, psbC, psbD, psbE, atpA). Heat shock-induced transcript accumulation is transitory with a maximum after an approximately 3 h exposure at high temperatures. On the other hand, the accumulation of rbcL transcript was only moderately thermosensitive. A temperature increase to 46-48 degrees C induces a sharp decrease of transcript levels which correlates with damage to the plant. Relatively little correlation has been noted between RNA and protein patterns. However, there is a remarkable coincidence between temperature dependence of the accumulation of transcripts and the temperature dependence (28-46 degrees C) of the synthesis of chloroplast-located heat shock proteins indicating that both processes may be related.