RESUMO
Agricultural crops are exposed to a range of daylengths, which act as important environmental cues for the control of developmental processes such as flowering. To explore the additional effects of daylength on plant function, we investigated the transcriptome of Arabidopsis (Arabidopsis thaliana) plants grown under short days (SD) and transferred to long days (LD). Compared with that under SD, the LD transcriptome was enriched in genes involved in jasmonic acid-dependent systemic resistance. Many of these genes exhibited impaired expression induction under LD in the phytochrome A (phyA), cryptochrome 1 (cry1), and cry2 triple photoreceptor mutant. Compared with that under SD, LD enhanced plant resistance to the necrotrophic fungus Botrytis cinerea This response was reduced in the phyA cry1 cry2 triple mutant, in the constitutive photomorphogenic1 (cop1) mutant, in the myc2 mutant, and in mutants impaired in DELLA function. Plants grown under SD had an increased nuclear abundance of COP1 and decreased DELLA abundance, the latter of which was dependent on COP1. We conclude that growth under LD enhances plant defense by reducing COP1 activity and enhancing DELLA abundance and MYC2 expression.
Assuntos
Arabidopsis/metabolismo , Ciclopentanos/metabolismo , Luz , Oxilipinas/metabolismo , Fotoperíodo , Arabidopsis/genética , Arabidopsis/microbiologia , Proteínas de Arabidopsis/genética , Botrytis/fisiologia , Criptocromos/genética , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Mutação , Fitocromo A/genética , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Plantas Geneticamente Modificadas , Transcriptoma/efeitos da radiação , Ubiquitina-Proteína Ligases/genéticaRESUMO
Plants have developed sophisticated systems to monitor and rapidly acclimate to environmental fluctuations. Light is an essential source of environmental information throughout the plant's life cycle. The model plant Arabidopsis thaliana possesses five phytochromes (phyA-phyE) with important roles in germination, seedling establishment, shade avoidance, and flowering. However, our understanding of the phytochrome signaling network is incomplete, and little is known about the individual roles of phytochromes and how they function cooperatively to mediate light responses. Here, we used a bottom-up approach to study the phytochrome network. We added each of the five phytochromes to a phytochrome-less background to study their individual roles and then added the phytochromes by pairs to study their interactions. By analyzing the 16 resulting genotypes, we revealed unique roles for each phytochrome and identified novel phytochrome interactions that regulate germination and the onset of flowering. Furthermore, we found that ambient temperature has both phytochrome-dependent and -independent effects, suggesting that multiple pathways integrate temperature and light signaling. Surprisingly, none of the phytochromes alone conferred a photoperiodic response. Although phyE and phyB were the strongest repressors of flowering, both phyB and phyC were needed to confer a flowering response to photoperiod. Thus, a specific combination of phytochromes is required to detect changes in photoperiod, whereas single phytochromes are sufficient to respond to light quality, indicating how phytochromes signal different light cues.
Assuntos
Apoproteínas/genética , Proteínas de Arabidopsis/genética , Arabidopsis/genética , Fitocromo B/genética , Fitocromo/genética , Apoproteínas/metabolismo , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/metabolismo , Genótipo , Germinação/genética , Luz , Fitocromo/metabolismo , Fitocromo A , Fitocromo B/metabolismo , Folhas de Planta/genética , Folhas de Planta/crescimento & desenvolvimento , Plântula/genética , Plântula/crescimento & desenvolvimento , Transdução de Sinais/genética , TemperaturaRESUMO
Phytochrome A (phyA) is crucial to initiate the early steps of the transition between skoto- and photomorphogenesis upon light exposure and to complete this process under far-red light (typical of dense vegetation canopies). However, under prolonged red or white light, phyA mutants are hyper-photomorphogenic in many respects. To investigate this issue, we analyzed the late response of the transcriptome of the phyA mutant to red light. Compared to the wild-type (WT), hyper-responsive genes outnumbered the genes showing reduced response to red light in phyA. A network analysis revealed the co-expression of PHYTOCHROME INTERACTING FACTOR 1 (PIF1) with those genes showing hyper-promotion by red light in phyA. The enhanced responses of gene expression, cotyledon unfolding, hypocotyl growth, and greening observed in the phyA mutant compared to the WT were absent in the phyA pif1 double mutant compared to pif1, indicating that the hyper-photomorphogenic phenotype of phyA requires PIF1. PIF1 directly binds to gene promoters that displayed PIF1-mediated enhanced response to red light. Expression of mutant PIF1 deficient in interactions with phyA and phyB enhanced the long-term growth response to red light but reduced the expression of selected genes in response to red light. We propose that phytochrome-mediated degradation of PIF1 prevents over-activation of photomorphogenesis during early seedling development.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Luz , Fitocromo A/metabolismo , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/química , Fatores de Transcrição Hélice-Alça-Hélice Básicos/química , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Mutação , Fitocromo A/genética , Fitocromo B/metabolismo , Estabilidade Proteica/efeitos da radiação , Estrutura Terciária de Proteína , Proteólise/efeitos da radiação , Plântula/crescimento & desenvolvimento , Plântula/efeitos da radiaçãoRESUMO
In etiolated seedlings, phytochrome A (phyA) mediates very-low-fluence responses (VLFRs), which initiate de-etiolation at the interphase between the soil and above-ground environments, and high-irradiance responses (HIR), which complete de-etiolation under dense canopies and require more sustained activation with far-red light. Light-activated phyA is transported to the nucleus by FAR-RED ELONGATED HYPOCOTYL1 (FHY1). The nuclear pool of active phyA increases under prolonged far-red light of relatively high fluence rates. This condition maximizes the rate of FHY1-phyA complex assembly and disassembly, allowing FHY1 to return to the cytoplasm to translocate further phyA to the nucleus, to replace phyA degraded in the proteasome. The core signalling pathways downstream of nuclear phyA involve the negative regulation of CONSTITUTIVE PHOTOMORPHOGENIC 1, which targets for degradation transcription factors required for photomorphogenesis, and PHYTOCHROME-INTERACTING FACTORs, which are transcription factors that repress photomorphogenesis. Under sustained far-red light activation, released FHY1 can also be recruited with active phyA to target gene promoters as a transcriptional activator, and nuclear phyA signalling activates a positive regulatory loop involving BELL-LIKE HOMEODOMAIN 1 that reinforces the HIR.
Assuntos
Transdução de Sinal Luminoso , Luz , Fitocromo A/metabolismo , Plantas/metabolismo , Plantas/efeitos da radiação , Meio Ambiente , Modelos BiológicosRESUMO
In Arabidopsis seeds, germination is promoted only by phytochromes, principally phytochrome B (phyB) and phytochrome A (phyA). Despite the abundant information concerning the molecular basis of phyB signaling downstream of PIF1/PIL5, the signaling network inducing germination by phyA is poorly known. Here, we describe the influence of phyA on the transcriptome of Arabidopsis seeds when germination is induced by a far-red (FR) pulse. The expression of 11% of the genome was significantly regulated by phyA. Most of the genes were up-regulated and the changes noted late (i.e. 5 h after a FR pulse), whereas changes in down-regulated genes were more abundant earlier (i.e. 0.5 h after a FR pulse). Auxin- and GA-associated elements were overrepresented in the genes that were modified by phyA. A significant number of genes whose expression was affected by phyA had not been previously reported to be dependent on PIL5. Among them, homozygotic mutant seeds of MYB66, a SAUR-like protein, PIN7, and GASA4 showed an impaired promotion of germination by phyA. Natural variation at the transcriptional level was found in early signaling and GA metabolic genes, but not in ABA metabolic and expansin genes between Columbia and Landsberg erecta accessions. Although phyA and phyB/PIL5 signaling pathways share some molecular components, our data suggest that phyA signaling is partially independent of PIL5 when germination is promoted by very low fluences of light.
Assuntos
Arabidopsis/genética , Arabidopsis/fisiologia , Germinação , Fitocromo A/metabolismo , Sementes/fisiologia , Transcrição Gênica , Arabidopsis/citologia , Arabidopsis/enzimologia , Proteínas de Arabidopsis/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , DNA Bacteriano/genética , Perfilação da Expressão Gênica , Giberelinas/genética , Mutação , Fitocromo A/genética , Reguladores de Crescimento de Plantas/genética , Transdução de Sinais , Fatores de Transcrição/metabolismoRESUMO
Stresses resulting from high transpiration demand induce adjustments in plants that lead to reductions of water loss. These adjustments, including changes in water absorption, transport and/or loss by transpiration, are crucial to normal plant development. Tomato wild type (WT) and phytochrome A (phyA)-mutant plants, fri1-1, were exposed to conditions of either low or high transpiration demand and several morphological and physiological changes were measured during stress conditions. Mutant plants rapidly wilted compared to WT plants after exposure to high evaporative demand. Root size and hydraulic conductivity did not show significant differences between genotypes, suggesting that water absorption and transport through this organ could not explain the observed phenotype. Moreover, stomatal density was similar between genotypes, whereas transpiration and stomatal conductance were both lower in mutant than in WT plants. This was accompanied by a lower stem-specific hydraulic conductivity in mutant plants, which was associated to lower xylem vessel number and transversal area in fri1-1 plants, producing a reduction in water supply to the leaves, which rapidly wilted under high evaporative demand. PhyA signaling might facilitate the adjustment to environments differing widely in water evaporative demand in part through the modulation of xylem dimensions.
Assuntos
Transporte Biológico/fisiologia , Fitocromo A/metabolismo , Transpiração Vegetal/fisiologia , Solanum lycopersicum/crescimento & desenvolvimento , Solanum lycopersicum/fisiologia , Água/metabolismo , Aclimatação , Variação Genética , Genótipo , Solanum lycopersicum/genética , Folhas de Planta/fisiologia , Raízes de Plantas/fisiologia , Caules de Planta/fisiologia , Estômatos de Plantas/fisiologia , Especificidade da Espécie , Estresse Fisiológico , Luz Solar , Xilema/metabolismoRESUMO
Although multiple photoreceptors converge to control common aspects of seedling de-etiolation, we are relatively ignorant of the genes acting at or downstream of their signalling convergence. To address this issue we screened for mutants under a mixture of blue plus far-red light and identified roc1-1D. The roc1-1D mutant, showing elevated expression of the ROTAMASE CYCLOPHILIN 1 (ROC1/AtCYP18-3) gene, and partial loss-of function roc1 alleles, has defects in phytochrome A (phyA)-, cryptochrome 1 (cry1)- and phytochrome B (phyB)-mediated de-etiolation, including long hypocotyls under blue or far-red light. These mutants show elevated sensitivity to brassinosteroids in the light but not in the dark. Mutations at brassinosteroid signalling genes and the application of a brassinosteroid synthesis inhibitor eliminated the roc1 and roc1-D phenotypes. The roc1 and roc1-D mutants show altered patterns of phosphorylation of the transcription factor BES1, a known point of control of sensitivity to brassinosteroids, which correlate with the expression levels of genes directly targeted by BES1. We propose a model where perception of light by phyA, cry1 or phyB activates ROC1 (at least in part by enhancing its expression). This in turn reduces the intensity of brassinosteroid signalling and fine-tunes seedling de-etiolation.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Criptocromos/metabolismo , Ciclofilinas/metabolismo , Proteínas Nucleares/metabolismo , Fitocromo A/metabolismo , Arabidopsis/genética , Brassinosteroides/metabolismo , Proteínas de Ligação a DNA , Luz , Mutação , Fenótipo , FosforilaçãoRESUMO
The light environment provides signals that play a critical role in the control of stem growth in plants. The reduced irradiance and altered spectral composition of shade light promote stem growth compared with unfiltered sunlight. However, whereas most studies have used seedlings exposed to contrasting but constant light treatments, the natural light environment may exhibit strong fluctuations. As a result of gaps in the canopy, plants shaded by neighbours may experience sunflecks, i.e., brief periods of exposure to unfiltered sunlight. Here, we show that sunflecks are perceived by phytochromes A and B, and inhibit hypocotyl growth in Arabidopsis thaliana mainly if they occur during the final portion of the photoperiod. By using forward and reverse genetic approaches we found that ELONGATED HYPOCOTYL 5, LATE ELONGATED HYPOCOTYL, PHYTOCHROME KINASE SUBSTRATE 4 and auxin signalling are key players in this response.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Proteínas Nucleares/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Fatores de Transcrição de Zíper de Leucina Básica/genética , Relógios Circadianos , Clonagem Molecular , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Hipocótilo/genética , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/metabolismo , Hipocótilo/efeitos da radiação , Peptídeos e Proteínas de Sinalização Intracelular , Proteínas Nucleares/genética , Fotoperíodo , Fitocromo A/genética , Fitocromo A/metabolismo , Fitocromo B/genética , Fitocromo B/metabolismo , Caules de Planta/genética , Caules de Planta/crescimento & desenvolvimento , Caules de Planta/metabolismo , Caules de Planta/efeitos da radiação , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Luz Solar , Fatores de TempoRESUMO
PREMISE OF THE STUDY: Little is known of the evolutionary relationships within Conopholis, a small holoparasitic genus belonging to the broomrape family. Presently, Conopholis is described as having two species, C. americana and C. alpina. This classification is based on a combination of presence/absence of morphological characters along with a number of quantitative traits. We assessed the relationships among populations and species of this genus to determine whether the present taxonomic hypothesis is reflected in molecular phylogenies. METHODS: We conducted the first phylogenetic study of Conopholis using plastid (trnfM-E intergenic spacer and clpP gene/introns) and nuclear (PHYA intron 1) sequences from a wide taxonomic sampling covering its entire geographical range in North America. Analyses were carried out using a variety of phylogenetic inference approaches. KEY RESULTS: Reciprocal monophyly between the two traditionally accepted species has not yet been achieved. Instead, three distinct genetic clusters were recovered. Conopholis alpina is clearly paraphyletic and shows evidence of belonging to at least two distinct lineages. Specimens found in Costa Rica and Panama form a distinct group from those located in northern Mexico and the southwestern United States. The monophyly of C. americana was also not recovered; however, the possibility of it being monophyletic could not be rejected with confidence. CONCLUSIONS: These analyses recovered three distinct lineages indicating that there could be a minimum of three species within the genus. A reevaluation of morphological features within Conopholis may reveal shared features that could further corroborate our molecular findings.
Assuntos
Núcleo Celular/genética , Orobanchaceae/genética , Plastídeos/genética , Canadá , DNA Intergênico/genética , DNA de Plantas/genética , Endopeptidase Clp/genética , Evolução Molecular , Genes de Plantas , México , Dados de Sequência Molecular , NADH Desidrogenase/genética , Orobanchaceae/classificação , Filogenia , Filogeografia , Fitocromo A/genética , Proteínas de Plantas/genética , Reação em Cadeia da Polimerase , Alinhamento de Sequência , Análise de Sequência de DNA , Estados UnidosRESUMO
Green light added to blue light has been proposed to shift cryptochromes from their semireduced active form to the reduced, inactive state. Whether the increased proportion of green light observed under leaf canopies compared to open places reduces cryptochrome-mediated effects remained to be elucidated. Here we report that the length of the hypocotyl of Arabidopsis (Arabidopsis thaliana) seedlings grown under controlled conditions decreased linearly with increasing blue/green ratios of the light within the range of ratios found in natural environments. This effect was stronger under higher irradiances. We developed a model, parameterized on the basis of field experiments including photoreceptor mutants, where hypocotyl growth of seedlings exposed to different natural radiation environments was related to the action and interaction of phytochromes and cryptochromes. Adding the blue/green ratio of the light in the term involving cryptochrome activity improved the goodness of fit of the model, thus supporting a role of the blue/green ratio under natural radiation. The blue/green ratio decreased sharply with increasing shade by green grass leaves to one-half of the values observed in open places. The impact of blue/green ratio on cryptochrome-mediated inhibition of hypocotyl growth was at least as large as that of irradiance. We conclude that cryptochrome is a sensor of blue irradiance and blue/green ratio.
Assuntos
Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Criptocromos/metabolismo , Luz , Arabidopsis/crescimento & desenvolvimento , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/efeitos da radiação , Modelos Biológicos , Fitocromo A/metabolismo , Fitocromo B/metabolismo , Folhas de Planta/metabolismo , Folhas de Planta/efeitos da radiaçãoRESUMO
Plant responses mediated by phytochrome A display a first phase saturated by transient light signals and a second phase requiring sustained excitation with far-red light (FR). These discrete outcomes, respectively so-called very-low-fluence response (VLFR) and high-irradiance response (HIR), are appropriate in different environmental and developmental contexts but the mechanisms that regulate the switch remain unexplored. Promoter analysis of a light-responsive target gene revealed a motif necessary for HIR but not for VLFR. This motif is required for binding of the Bell-like homeodomain 1 (BLH1) to the promoter in in vitro and in yeast 1-hybrid experiments. Promoter substitutions that increased BLH1 binding also enhanced HIR. blh1 mutants showed reduced responses to continuous FR and to deep canopy shadelight, but they retained normal responses to pulsed FR or red light and unfiltered sunlight. BLH1 enhanced BLH1 expression and its promotion by FR. We conclude that BLH1 specifically regulates HIR and not VLFR of phytochrome A.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Proteínas de Homeodomínio/metabolismo , Luz , Fitocromo A/metabolismo , Fatores de Transcrição/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Sequência de Bases , Perfilação da Expressão Gênica , Mutação/genética , Regiões Promotoras Genéticas/genética , Ligação Proteica/efeitos da radiação , Nicotiana , Fatores de Transcrição/genéticaRESUMO
GIGANTEA (GI) is a nuclear protein involved in the promotion of flowering by long days, in light input to the circadian clock, and in seedling photomorphogenesis under continuous red light but not far-red light (FR). Here, we report that in Arabidopsis (Arabidopsis thaliana) different alleles of gi have defects in the hypocotyl-growth and cotyledon-unfolding responses to hourly pulses of FR, a treatment perceived by phytochrome A (phyA). This phenotype is rescued by overexpression of GI. The very-low-fluence response of seed germination was also reduced in gi. Since the circadian clock modulates many light responses, we investigated whether these gi phenotypes were due to alterations in the circadian system or light signaling per se. In experiments where FR pulses were given to dark-incubated seeds or seedlings at different times of the day, gi showed reduced seed germination, cotyledon unfolding, and activity of a luciferase reporter fused to the promoter of a chlorophyll a/b-binding protein gene; however, rhythmic sensitivity was normal in these plants. We conclude that while GI does not affect the high-irradiance responses of phyA, it does affect phyA-mediated very-low-fluence responses via mechanisms that do not obviously involve its circadian functions.
Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Ritmo Circadiano , Luz , Fitocromo A/metabolismo , Alelos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cotilédone/genética , Cotilédone/crescimento & desenvolvimento , Cotilédone/metabolismo , Flores/genética , Flores/crescimento & desenvolvimento , Flores/metabolismo , Germinação , Hipocótilo/genética , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/metabolismo , Fenótipo , Sementes/crescimento & desenvolvimento , Sementes/metabolismo , Transdução de SinaisRESUMO
Deletion or substitution of the serine-rich N-terminal stretch of grass phytochrome A (phyA) has repeatedly been shown to yield a hyperactive photoreceptor when expressed under the control of a constitutive promoter in transgenic tobacco or Arabidopsis seedlings retaining their native phyA. These observations have lead to the proposal that the serine-rich region is involved in negative regulation of phyA signaling. To re-evaluate this conclusion in a more physiological context we produced transgenic Arabidopsis seedlings of the phyA-null background expressing Arabidopsis PHYA deleted in the sequence corresponding to amino acids 6-12, under the control of the native PHYA promoter. Compared to the transgenic seedlings expressing wild-type phyA, the seedlings bearing the mutated phyA showed normal responses to pulses of far-red (FR) light and impaired responses to continuous FR light. In yeast two-hybrid experiments, deleted phyA interacted normally with FHY1 and FHL, which are required for phyA accumulation in the nucleus. Immunoblot analysis showed reduced stability of deleted phyA under continuous red or FR light. The reduced physiological activity can therefore be accounted for by the enhanced destruction of the mutated phyA. These findings do not support the involvement of the serine-rich region in negative regulation but they are consistent with a recent report suggesting that phyA turnover is regulated by phosphorylation.
Assuntos
Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/fisiologia , Arabidopsis/genética , Fitocromo A/química , Fitocromo A/fisiologia , Serina/análise , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Ritmo Circadiano , Germinação , Luz , Fitocromo A/deficiência , Fitocromo A/genética , Plantas Geneticamente Modificadas , Plântula/genética , Transdução de SinaisRESUMO
We used 52 Arabidopsis (Arabidopsis thaliana) accessions and developed a new set of 137 recombinant inbred lines between Landsberg erecta (Ler) and Nossen (No-0) to explore the genetic basis of phytochrome-mediated responses during deetiolation. Unexpectedly, most accessions showed weak or moderate hypocotyl growth and cotyledon unfolding responses to pulses of far-red light (FR). Crosses between Columbia and No-0, two accessions with poor response, segregated seedlings with unfolded cotyledons under pulsed FR, suggesting the occurrence of accession-specific loci in the repression of morphological responses to weak light signals. Confirming the latter expectation, mapping of responses to pulsed FR in the Ler x No-0 lines identified novel loci. Despite its weak response to pulsed FR, No-0 showed a response to continuous FR stronger than that observed in Ler. By mapping the differential effect of pulsed versus continuous FR, we identified two high-irradiance response loci that account for the steeper response to continuous FR in No-0. This underscores the potential of the methodology to identify loci involved in the regulation of the shape of signal input-output relationships. Loci specific for a given phytochrome-mediated response were more frequent than pleiotropic loci. Segregation of these specific loci is predicted to yield different combinations of seedling responsivity to light. Such flexibility in combination of responses is observed among accessions and could aid in the adjustment to different microenvironments.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/fisiologia , Arabidopsis/genética , Arabidopsis/fisiologia , Fitocromo/genética , Fitocromo/fisiologia , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/fisiologia , Mapeamento Cromossômico , Cromossomos de Plantas , Cotilédone/crescimento & desenvolvimento , Cruzamentos Genéticos , Ligação Genética , Variação Genética , Hipocótilo/crescimento & desenvolvimento , Endogamia , Raios Infravermelhos , Fitocromo A , Locos de Características QuantitativasRESUMO
CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) represses photomorphogenesis in darkness by targeting nuclear-localized transcription factors to proteasome-mediated degradation. Upon light exposure, COP1 migrates to the cytosol allowing photomorphogenesis to proceed but the residual nuclear pool down-regulates light signaling mediated by phytochrome A. Here we show that weak alleles of cop1 exhibit reverse photomorphogenic responses i.e. reduced rather than enhanced cotyledon unfolding under red light compared to darkness. Conversely, COP1 overexpressors which de-etiolate poorly under blue or far-red light, showed enhanced photomorphogenesis under red light. The positive relationship between COP1 and photomorphogenic response required phytochrome B. Thus, genetic manipulation of COP1 levels differentially affects phytochrome A- compared to phytochrome B-mediated responses. We hypothesize that COP1 could be involved in degradation of negative regulators of photomorphogenesis or in transcriptional activation, as observed for some E3 ligases in mammalian development.
Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Morfogênese/efeitos da radiação , Ubiquitina-Proteína Ligases/fisiologia , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Hipocótilo/genética , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/efeitos da radiação , Luz , Modelos Biológicos , Morfogênese/genética , Mutação , Células Fotorreceptoras/fisiologia , Fitocromo/genética , Fitocromo/fisiologia , Fitocromo A , Fitocromo B , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/fisiologia , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologia , Ubiquitina-Proteína Ligases/genéticaRESUMO
Several mutants with altered phytochrome A (phyA) signalling have been identified in screenings under continuous far-red light (FR). The latter protocol could preclude the identification of mutants affected in the signalling pathway that operates even under transient phyA activation, compared to the high-irradiance response (HIR) pathway that requires continuous FR. Since some photomorphogenic mutants show shoot-height phenotypes, the screening was conducted on dwarf mutants of Arabidopsis thaliana (L.) Heynh. from the ABRC stocks grown under hourly FR pulses. The dwarf mutant cp3 (compacta 3) showed normal hypocotyl length and folded cotyledons in darkness but enhanced hypocotyl-growth inhibition and cotyledon unfolding under pulsed FR. The HIR and the response mediated by phyB were not affected. Under pulsed FR, seed germination and blocking of greening upon transfer to white light were enhanced in cp3. PHYA levels were normal in cp3. The phenotype under pulsed FR but not the adult phenotype required phyA. We propose that CP3 is involved in the negative regulation of the signalling pathway that saturates with transient activation of phyA.
Assuntos
Arabidopsis/crescimento & desenvolvimento , Células Fotorreceptoras , Fitocromo/metabolismo , Transdução de Sinais/fisiologia , Fatores de Transcrição , Adaptação Fisiológica/genética , Antocianinas/biossíntese , Antocianinas/efeitos da radiação , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis , Clorofila/biossíntese , Clorofila/efeitos da radiação , Cotilédone/genética , Cotilédone/crescimento & desenvolvimento , Cotilédone/efeitos da radiação , Escuridão , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Hipocótilo/genética , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/efeitos da radiação , Luz , Mutação , Fenótipo , Fotoperíodo , Fotossíntese/genética , Fotossíntese/fisiologia , Fotossíntese/efeitos da radiação , Fitocromo A , Fitocromo B , Sementes/genética , Sementes/crescimento & desenvolvimento , Sementes/efeitos da radiação , Transdução de Sinais/efeitos da radiaçãoRESUMO
Phytochrome (phy) A mediates two distinct photobiological responses in plants: the very-low-fluence response (VLFR), which can be saturated by short pulses of very-low-fluence light, and the high-irradiance response (HIR), which requires prolonged irradiation with higher fluences of far-red light (FR). To investigate whether the VLFR and HIR involve different domains within the phyA molecule, transgenic tobacco (Nicotiana tabacum cv Xanthi) and Arabidopsis seedlings expressing full-length (FL) and various deletion mutants of oat (Avena sativa) phyA were examined for their light sensitivity. Although most mutants were either partially active or inactive, a strong differential effect was observed for the Delta6-12 phyA mutant missing the serine-rich domain between amino acids 6 and 12. Delta6-12 phyA was as active as FL phyA for the VLFR of hypocotyl growth and cotyledon unfolding in Arabidopsis, and was hyperactive in the VLFR of hypocotyl growth and cotyledon unfolding in tobacco, and the VLFR blocking subsequent greening under white light in Arabidopsis. In contrast, Delta6-12 phyA showed a dominant-negative suppression of HIR in both species. In hypocotyl cells of Arabidopsis irradiated with FR phyA:green fluorescent protein (GFP) and Delta6-12 phyA:GFP fusions localized to the nucleus and coalesced into foci. The proportion of nuclei with abundant foci was enhanced by continuous compared with hourly FR provided at equal total fluence in FL phyA:GFP, and by Delta6-12 phyA mutation under hourly FR. We propose that the N-terminal serine-rich domain of phyA is involved in channeling downstream signaling via the VLFR or HIR pathways in different cellular contexts.
Assuntos
Avena/fisiologia , Núcleo Celular/metabolismo , Fitocromo/metabolismo , Serina/metabolismo , Antocianinas/metabolismo , Arabidopsis/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis , Avena/genética , Avena/efeitos da radiação , Proteínas de Fluorescência Verde , Hipocótilo/crescimento & desenvolvimento , Luz , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Microscopia de Fluorescência , Mutação , Fotossíntese/fisiologia , Fotossíntese/efeitos da radiação , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/efeitos da radiação , Fitocromo/química , Fitocromo/genética , Fitocromo A , Plantas Geneticamente Modificadas , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Sementes/genética , Sementes/fisiologia , Sementes/efeitos da radiação , Transdução de Sinais/fisiologia , Nicotiana/genética , Nicotiana/fisiologiaRESUMO
Phytochrome A signaling shows two photobiologically discrete outputs: so-called very-low-fluence responses (VLFR) and high-irradiance responses (HIR). By modifying previous screening protocols, we isolated two Arabidopsis mutants retaining VLFR and lacking HIR. Phytochrome A negatively or positively regulates phytochrome B signaling, depending on light conditions. These mutants retained the negative but lacked the positive regulation. Both mutants carry the novel phyA-302 allele, in which Glu-777 (a residue conserved in angiosperm phytochromes) changed to Lys in the PAS2 motif of the C-terminal domain. The phyA-302 mutants showed a 50% reduction in phytochrome A levels in darkness, but this difference was compensated for by greater stability under continuous far-red light. phyA-302:green fluorescent protein fusion proteins showed normal translocation from the cytosol to the nucleus under continuous far-red light but failed to produce nuclear spots, suggesting that nuclear speckles could be involved in HIR signaling and phytochrome A degradation. We propose that the PAS2 domain of phytochrome A is necessary to initiate signaling in HIR but not in VLFR, likely via interaction with a specific partner.
Assuntos
Mutação de Sentido Incorreto/genética , Proteínas Nucleares/genética , Proteínas de Transporte Nucleocitoplasmático/metabolismo , Células Fotorreceptoras , Fitocromo/genética , Fatores de Transcrição , Alelos , Antocianinas/biossíntese , Arabidopsis/genética , Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis , Sítios de Ligação/genética , Transporte Biológico/efeitos da radiação , Sequência Conservada/genética , Escuridão , Teste de Complementação Genética , Germinação , Proteínas de Fluorescência Verde , Hipocótilo/crescimento & desenvolvimento , Luz , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Microscopia de Fluorescência , Proteínas Nucleares/metabolismo , Proteínas Nucleares/efeitos da radiação , Proteínas de Transporte Nucleocitoplasmático/genética , Proteínas de Transporte Nucleocitoplasmático/efeitos da radiação , Fitocromo/metabolismo , Fitocromo/efeitos da radiação , Fitocromo A , Fitocromo B , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Recombinantes de Fusão/efeitos da radiação , Sementes/crescimento & desenvolvimento , Transdução de Sinais/genética , Transdução de Sinais/efeitos da radiação , Fatores de TempoRESUMO
Phytochromes (phy) A and B provide higher plants the ability to perceive divergent light signals. phyB mediates red/far-red light reversible, low fluence responses (LFR). phyA mediates both very-low-fluence responses (VLFR), which saturate with single or infrequent light pulses of very low fluence, and high irradiance responses (HIR), which require sustained activation with far-red light. We investigated whether VLFR, LFR, and HIR are genetically coregulated. The Arabidopsis enhanced very-low-fluence response1 mutant, obtained in a novel screening under hourly far-red light pulses, showed enhanced VLFR of hypocotyl growth inhibition, cotyledon unfolding, blocking of greening, and anthocyanin synthesis. However, eve1 showed reduced LFR and HIR. eve1 was found allelic to the brassinosteroid biosynthesis mutant dim/dwarf1. The analysis of both the brassinosteroid mutant det2 in the Columbia background (where VLFR are repressed) and the phyA eve1 double mutant indicates that the negative effect of brassinosteroid mutations on LFR requires phyA signaling in the VLFR mode but not the expression of the VLFR. Under sunlight, hypocotyl growth of eve1 showed little difference with the wild type but failed to respond to canopy shadelight. We propose that the opposite regulation of VLFR versus LFR and HIR could be part of a context-dependent mechanism of adjustment of sensitivity to light signals.
Assuntos
Proteínas de Arabidopsis , Arabidopsis/fisiologia , Colestanóis/metabolismo , Células Fotorreceptoras , Fitocromo/fisiologia , Esteroides Heterocíclicos/metabolismo , Fatores de Transcrição , Antocianinas/biossíntese , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Brassinosteroides , Clorofila/biossíntese , Cotilédone/fisiologia , Cotilédone/efeitos da radiação , Cruzamentos Genéticos , Hipocótilo/crescimento & desenvolvimento , Hipocótilo/efeitos da radiação , Luz , Mutação , Fenótipo , Fitocromo A , Fitocromo B , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Proteínas de Plantas/efeitos da radiação , Transdução de Sinais/efeitos da radiaçãoRESUMO
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.