RESUMO
In plants, development is a continuing process that takes place under strong fluctuations of the light environment. Here we show that in Arabidopsis thaliana plants grown under intense white light, coupling of the photoreceptor cryptochrome 2 to developmental processes is broader than previously appreciated. Compared to the wild type, the cry2 mutant showed reduced activity of a Lhcb1*2 promoter fused to a reporter, and delayed flowering. The cry2 mutation also reduced the inhibition of hypocotyl growth, the unfolding of the cotyledons, the rate of leaf production during the vegetative phase, and the pace of development after transition to the reproductive stage; but these effects were obvious only in the absence of cryptochrome 1 and in some cases phytochrome A and/or phytochrome B. Complementary, the cry2 mutation uncovered novel roles for cryptochrome 1 and phytochrome A. The activity of the Lhcb1*2 promoter was higher in the cry1 cry2 mutant than in the cry2 mutant, suggesting that cry1 could be involved in blue-light repression of photosynthetic genes. Surprisingly, the phyA cry1 cry2 triple mutant flowered earlier and showed better response to photoperiod than the cry1 cry2 double mutant, indicating that phyA is involved in light repression of flowering. Growth and development were severely impaired in the quadruple phyA phyB cry1 cry2 mutant. We propose that stability and light modulation of development are achieved by simultaneous coupling of phytochrome A, phytochrome B, cryptochrome 1 and cryptochrome 2 to developmental processes, in combination with context-dependent hierarchy of their relative activities.
Assuntos
Proteínas de Drosophila , Proteínas do Olho , Flavoproteínas/fisiologia , Células Fotorreceptoras de Invertebrados , Células Fotorreceptoras , Complexo de Proteínas do Centro de Reação Fotossintética , Fitocromo/fisiologia , Fatores de Transcrição , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis , Cotilédone/fisiologia , Criptocromos , Flavoproteínas/genética , Luz , Fenótipo , Complexo de Proteínas do Centro de Reação Fotossintética/genética , Fitocromo/genética , Fitocromo A , Fitocromo B , Folhas de Planta/fisiologia , Receptores Acoplados a Proteínas G , Fatores de TempoRESUMO
Current evidence is inconclusive regarding the point of signaling convergence downstream from different members of the phytochrome family. In transgenic Arabidopsis, the activity of a reporter enzyme under the control of the -453 to +67 fragment of an Lhcb1*2 promoter shows very low fluence responses (VLFRs) and high-irradiance responses (HIRs) mediated by phytochrome A and low-fluence responses (LFRs) mediated by phytochrome B. A 5' deletion of the promoter to -134 abolished the HIR without affecting VLFR or LFR. In transgenic tobacco, VLFR and LFR were observed for the -176 to -31 or -134 to -31 fragments of Lhcb1*2 fused to 35S cauliflower mosaic virus minimal promoters, but only the largest fragment showed HIR. We propose that sustained activation of phytochrome A with far-red light initiates a signaling cascade that deviates from phytochrome B signaling and transient phytochrome A signaling and that this divergence extends as far as the Lhcb1*2 promoter.
Assuntos
Células Fotorreceptoras , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Fitocromo/metabolismo , Regiões Promotoras Genéticas , Transdução de Sinais , Fatores de Transcrição , Arabidopsis/metabolismo , Proteínas de Arabidopsis , Sequência de Bases , Caulimovirus/genética , Primers do DNA , Fitocromo A , Fitocromo B , Plantas Geneticamente ModificadasRESUMO
Phytochrome A (phyA) and phytochrome B (phyB) share the control of many processes but little is known about mutual signaling regulation. Here, we report on the interactions between phyA and phyB in the control of the activity of an Lhcb1*2 gene fused to a reporter, hypocotyl growth and cotyledon unfolding in etiolated Arabidopsis thaliana. The very-low fluence responses (VLFR) induced by pulsed far-red light and the high-irradiance responses (HIR) observed under continuous far-red light were absent in the phyA and phyA phyB mutants, normal in the phyB mutant, and reduced in the fhy1 mutant that is defective in phyA signaling. VLFR were also impaired in Columbia compared to Landsberg erecta. The low-fluence responses (LFR) induced by red-light pulses and reversed by subsequent far-red light pulses were small in the wild type, absent in phyB and phyA phyB mutants but strong in the phyA and fhy1 mutants. This indicates a negative effect of phyA and FHY1 on phyB-mediated responses. However, a pre-treatment with continuous far-red light enhanced the LFR induced by a subsequent red-light pulse. This enhancement was absent in phyA, phyB, or phyA phyB and partial in fhy1. The levels of phyB were not affected by the phyA or fhy1 mutations or by far-red light pre-treatments. We conclude that phyA acting in the VLFR mode (i.e. under light pulses) is antagonistic to phyB signaling whereas phyA acting in the HIR mode (i.e. under continuous far-red light) operates synergistically with phyB signaling, and that both types of interaction require FHY1.
Assuntos
Arabidopsis/fisiologia , Complexos de Proteínas Captadores de Luz , Células Fotorreceptoras , Complexo de Proteína do Fotossistema II , Fitocromo/metabolismo , Fatores de Transcrição , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis , Relação Dose-Resposta à Radiação , Genes Reporter , Luz , Mutação , Complexo de Proteínas do Centro de Reação Fotossintética/biossíntese , Fitocromo/isolamento & purificação , Fitocromo A , Fitocromo B , Plantas Geneticamente Modificadas , Transdução de Sinais , Especificidade da EspécieRESUMO
The kinetics of phototransduction of phytochrome A (phyA) and phytochrome B (phyB) were compared in etiolated Arabidopsis thaliana seedlings. The responses of hypocotyl growth, cotyledon unfolding, and expression of a light-harvesting chlorophyll a/b-binding protein of the photosystem II gene promoter fused to the coding region of beta-glucuronidase (used as a reporter enzyme) were mediated by phyA under continuous far-red light (FR) and by phyB under continuous red light (R). The seedlings were exposed hourly either to n min of FR followed by 60 minus n min in darkness or to n min of R, 3 min of FR (to back-convert phyB to its inactive form), and 57 minus n min of darkness. For the three processes investigated here, the kinetics of phototransduction of phyB were faster than that of phyA. For instance, 15 min R h-1 (terminated with a FR pulse) were almost as effective as continuous R, whereas 15 min of FR h-1 caused less than 30% of the effect of continuous FR. This difference is interpreted in terms of divergence of signal transduction pathways downstream from phyA and phyB.
Assuntos
Arabidopsis/efeitos da radiação , Células Fotorreceptoras , Fitocromo/metabolismo , Transdução de Sinais/efeitos da radiação , Fatores de Transcrição , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis , Glucuronidase/genética , Luz , Fitocromo A , Fitocromo B , Regiões Promotoras GenéticasRESUMO
The occurrence of very-low-fluence responses (VLFR), low-fluence responses (LFR) and high-irradiance responses (HIR) of phytochrome was investigated for the expression of the gene of beta-glucuronidase (gusA) under the control of the tobacco Lhcb1*2 promoter, in etiolated transgenic tobacco seedlings. The activity of beta-glucuronidase (GUS) showed biphasic responses to the calculated proportion of Pfr provided by light pulses. The first phase (i.e. the VLFR) showed a maximum for Pfr levels characteristic of far-red light. The second phase (i.e. the LFR) was observed at higher Pfr levels and was reversible by far-red light pulses. The strong effect of continuous far-red light (i.e. HIR) was fluence-rate-dependent and could not be replaced either by hourly pulses of the same spectral composition and total fluence or by very low fluences of red light. Deletion of the Lhcb1*2 promoter to -453 caused little loss of GUS activity. The -453 to -31, -270 to -31 and -176 to -31 fragments of the Lhcb1*2 promoter conferred proportionally normal VLFR, LFR and HIR to a truncated (-46 to +8) CaMV 35S minimal promoter. This is the first demonstration of the presence of three phytochrome action modes in the control of the transcriptional activity of a single gene. The cis-acting regulatory elements necessary for VLFR, LFR and HIR are present in a 146 bp fragment of the tobacco Lhcb1*2 promoter.
Assuntos
Caulimovirus/genética , Nicotiana/fisiologia , Fitocromo/fisiologia , Plantas Tóxicas , Regiões Promotoras Genéticas , Sequência de Bases , Expressão Gênica/efeitos da radiação , Glucuronidase/biossíntese , Cinética , Luz , Dados de Sequência Molecular , Fitocromo/efeitos da radiação , Regiões Promotoras Genéticas/genética , Proteínas Recombinantes de Fusão/biossíntese , Nicotiana/genéticaRESUMO
A potato (Solanum tuberosum) genomic library was used to isolate five full-length genes and part of a sixth one, encoding the apoproteins of a light-harvesting complex (LHC). The nucleotide sequences of the five isolated genes showed that they encoded very similar proteins (99.75% to 97.50% identities). The deduced amino acid sequences were homologous to the PSII type I CAB proteins encoded by the Lhcb1 genes. The 5'-flanking regions of the five potato genes shared conserved sequences already detected in other light-responsive genes (62 bp fragment located between the CAAT and TATA boxes containing three GATA motifs). The expression of Lhcb1 genes in potato leaves, stems and roots was analyzed by the primer extension method. At least nine different transcripts can be recognized in leaves. A unique transcript could be detected in stems and not in roots. The regulatory function of the 5'-flanking region of the potato Lhcb1*2 was analyzed in transgenic tobacco plants. The construct used contained the gusA gene which was under the control of the potato Lhcb1*2 promoter. Analysis of transgenic plants revealed that the 5'-flanking region (-1300 to +10, relative to the transcription start site) of the Lhcb1*2 gene was sufficient to confer a phytochrome response as well as organ-specific expression.
Assuntos
Proteínas de Transporte/genética , Complexo de Proteínas do Centro de Reação Fotossintética , Complexo de Proteína do Fotossistema II , Proteínas de Plantas , Regiões Promotoras Genéticas , Solanum tuberosum/genética , Sequência de Bases , DNA de Plantas , Expressão Gênica , Dados de Sequência Molecular , Homologia de Sequência do Ácido NucleicoRESUMO
Analysis of a clinical isolate of Acinetobacter baumannii showed that this bacterium was able to grow under iron-limiting conditions, using chemically defined growth media containing different iron chelators such as human transferrin, ethylenediaminedi-(o-hydroxyphenyl)acetic acid, nitrilotriacetic acid, and 2,2'-bipyridyl. This iron uptake-proficient phenotype was due to the synthesis and secretion of a catechol-type siderophore compound. Utilization bioassays using the Salmonella typhimurium iron uptake mutants enb-1 and enb-7 proved that this siderophore is different from enterobactin. This catechol siderophore was partially purified from culture supernatants by adsorption chromatography using an XAD-7 resin. The purified component exhibited a chromatographic behavior and a UV-visible light absorption spectrum different from those of 2,3-dihydroxybenzoic acid and other bacterial catechol siderophores. Furthermore, the siderophore activity of this extracellular catechol was confirmed by its ability to stimulate energy-dependent uptake of 55Fe(III) as well as to promote the growth of A. baumannii bacterial cells under iron-deficient conditions imposed by 60 microM human transferrin. Polyacrylamide gel electrophoresis analysis showed the presence of iron-regulated proteins in both inner and outer membranes of this clinical isolate of A. baumannii. Some of these membrane proteins may be involved in the recognition and internalization of the iron-siderophore complexes.
Assuntos
Acinetobacter calcoaceticus/metabolismo , Ferro/metabolismo , Sideróforos/metabolismo , Transporte Biológico , Catecóis/isolamento & purificação , Catecóis/metabolismo , Regulação Bacteriana da Expressão Gênica/efeitos dos fármacos , Ferro/farmacologia , Proteínas de Membrana/biossíntese , Proteínas de Membrana/efeitos dos fármacos , Sideróforos/química , Sideróforos/isolamento & purificação , Transferrina/metabolismoRESUMO
Se trataron 55 pacientes portadores de una litiasis renal o ureteral alta con cirugía percutánea. El porcentaje global de éxito fue de 100% con 3,6% de cálculos residuales. Se utilizó anestesia peridural en todos los enfermos. No hubo mortalidad y la morbilidad fue baja. El promedio día de estadía fue de 4,5. Se analiza la relación entre la dilatación pielocalicial, la dificultad de punción y las complicaciones operatorias. También la relación entre el tipo de cálculo y las complicaciones operatorias
Assuntos
Pessoa de Meia-Idade , Humanos , Masculino , Feminino , Cálculos Renais/cirurgia , Cálculos Ureterais/cirurgia , Nefrostomia Percutânea/estatística & dados numéricos , LitotripsiaRESUMO
A lipid-bound oligosaccharide was isolated from pea (Pisum sativum) cotyledons incubated with [(14)C]mannose. The oligosaccharide moiety appeared to be identical with the one obtained from rat liver, known to contain three glucoses, nine mannoses, and two N-acetylglucosamines, and to be involved in protein glycosylation.Enzymes obtained from soya (Glycine max) roots and developing pea cotyledons were found to catalyze the transfer of oligosaccharide from the lipid intermediate to endogenous protein. The enzymes require Mn(2+) and detergent for activity. Evidence is presented indicating that the lipid-bound oligosaccharide with three glucoses is transferred faster than that with less. Some of the peripheral mannoses could be removed without affecting the rate of transfer.The protein-bound oligosaccharide, formed by incubation of whole cotyledons or by transfer with the enzyme preparation, could be released by protease and endo-beta-N-acetylglucosaminidase treatment, as expected for an asparagine-bound high mannose oligosaccharide.