RESUMO
Jeanette Snyder Brown (universally called Jan) was associated with the Department of Plant Biology, Carnegie Institution for Science (until recently Carnegie Institution of Washington) over a period of 37 years. Jan has left a scientific legacy of extensive publications concerned with photosynthetic pigments and their organization, and a historic collection of portraits of scientists who were prominent during her long tenure in the Department of Plant Biology. This legacy will stand for many years to come.
Assuntos
Botânica/história , História do Século XX , História do Século XXI , Estados UnidosRESUMO
BACKGROUND: One of the best-known plant movements, phototropic solar tracking in sunflower (Helianthus annuus), has not yet been fully characterized. Two questions are still a matter of debate. (1) Is the adaptive significance solely an optimization of photosynthesis via the exposure of the leaves to the sun? (2) Is shade avoidance involved in this process? In this study, these concepts are discussed from a historical perspective and novel insights are provided. SCOPE AND METHODS: Results from the primary literature on heliotropic growth movements led to the conclusion that these responses cease before anthesis, so that the flowering heads point to the East. Based on observations on 10-week-old plants, the diurnal East-West oscillations of the upper fifth of the growing stem and leaves in relation to the position of the sun (inclusive of nocturnal re-orientation) were documented, and photon fluence rates on the leaf surfaces on clear, cloudy and rainy days were determined. In addition, the light-response curve of net CO2 assimilation was determined on the upper leaves of the same batch of plants, and evidence for the occurrence of shade-avoidance responses in growing sunflower plants is summarized. CONCLUSIONS: Only elongating, vegetative sunflower shoots and the upper leaves perform phototropic solar tracking. Photon fluence response and CO2 assimilation measurements cast doubt on the 'photosynthesis-optimization hypothesis' as the sole explanation for the evolution of these plant movements. We suggest that the shade-avoidance response, which maximizes light-driven CO2 assimilation, plays a major role in solar tracking populations of competing sunflower plants, and an integrative scheme of these growth movements is provided.
Assuntos
Helianthus/fisiologia , Fototropismo/fisiologia , Luz Solar , Movimento , Fotossíntese , Terminologia como AssuntoRESUMO
The 14-3-3 λ isoform is required for normal stomatal opening mediated by PHOT2 in Arabidopsis thaliana. Arabidopsis phototropin2 (PHOT2) interacts with the λ-isoform 14-3-3 protein both in yeast two-hybrid screening and in an in vitro pull-down assay. Further yeast two-hybrid analysis also showed that the PHOT2 C-terminal kinase domain was required for the interaction. Site-directed mutagenesis indicated that PHOT2 Ser-747 is essential for the yeast interaction. Phenotypic characterization of a loss-of-function 14-3-3 λ mutant in a phot1 mutant background showed that the 14-3-3 λ protein was necessary for normal PHOT2-mediated blue light-induced stomatal opening. PHOT2 Ser-747 was necessary for complementation of the blue light-activated stomatal response in a phot1 phot2 double mutant. The 14-3-3 λ mutant in the phot1 mutant background allowed normal phototropism and normal chloroplast accumulation and avoidance responses. It also showed normal stomatal opening mediated by PHOT1 in a phot2 mutant background. The 14-3-3 κ mutant had no effect on stomatal opening in response to blue light. Although the 14-3-3 λ mutant had no chloroplast movement phenotype, the 14-3-3 κ mutation caused a weaker avoidance response at an intermediate blue light intensity by altering the balance between the avoidance and accumulation responses. The results highlight the strict specificity of phototropin-mediated signal transduction pathways.
Assuntos
Proteínas 14-3-3/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Estômatos de Plantas/fisiologia , Proteínas 14-3-3/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Cloroplastos/fisiologia , Teste de Complementação Genética , Luz , Mutagênese Sítio-Dirigida , Fototropismo , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/fisiologia , Isoformas de Proteínas , Transdução de Sinais , Técnicas do Sistema de Duplo-HíbridoRESUMO
Plants adapt to environmental light conditions by photoreceptor-mediated physiological responses, but the mechanism by which photoreceptors perceive and transduce the signals is still unresolved. Here, we used 2D difference gel electrophoresis (2D DIGE) and mass spectrometry to characterize early molecular events induced by short blue light exposures in etiolated Arabidopsis seedlings. We observed the phosphorylation of phototropin 1 (phot1) and accumulation of weak chloroplast movement under blue light 1 (WEB1) in the membrane fraction after blue light irradiation. Over 50 spots could be observed for the two rows of phot1 spots in the 2-DE gels, and eight novel phosphorylated Ser/Thr sites were identified in the N-terminus and Hinge 1 regions of phot1 in vivo. Blue light caused ubiquitination of phot1, and K526 of phot1 was identified as a putative ubiquitination site. Our study indicates that post-translational modification of phot1 is more complex than previously reported.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/efeitos da radiação , Luz , Proteoma/metabolismo , Proteômica/métodos , Plântula/efeitos da radiação , Sequência de Aminoácidos , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Sítios de Ligação/genética , Western Blotting , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Cromatografia Líquida , Eletroforese em Gel Bidimensional , Estiolamento/efeitos da radiação , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Espectrometria de Massas , Dados de Sequência Molecular , Fosfopeptídeos/genética , Fosfopeptídeos/metabolismo , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Fosforilação/efeitos da radiação , Proteínas Serina-Treonina Quinases , Proteoma/genética , Plântula/genética , Plântula/metabolismo , Homologia de Sequência de Aminoácidos , Serina/metabolismo , Treonina/metabolismoRESUMO
Abiotic chemical signals discovered in smoke that are known as karrikins (KARs) and the endogenous hormone strigolactone (SL) control plant growth through a shared MORE AXILLARY GROWTH2 (MAX2)-dependent pathway. A SL biosynthetic pathway and candidate KAR/SL receptors have been characterized, but signaling downstream of MAX2 is poorly defined. A screen for genetic suppressors of the enhanced seed dormancy phenotype of max2 in Arabidopsis (Arabidopsis thaliana) led to identification of a suppressor of max2 1 (smax1) mutant. smax1 restores the seed germination and seedling photomorphogenesis phenotypes of max2 but does not affect the lateral root formation, axillary shoot growth, or senescence phenotypes of max2. Expression of three transcriptional markers of KAR/SL signaling, D14-LIKE2, KAR-UP F-BOX1, and INDOLE-3-ACETIC ACID INDUCIBLE1, is rescued in smax1 max2 seedlings. SMAX1 is a member of an eight-gene family in Arabidopsis that has weak similarity to HEAT SHOCK PROTEIN 101, which encodes a caseinolytic peptidase B chaperonin required for thermotolerance. SMAX1 and the SMAX1-like (SMXL) homologs are differentially expressed in Arabidopsis tissues. SMAX1 transcripts are most abundant in dry seed, consistent with its function in seed germination control. Several SMXL genes are up-regulated in seedlings treated with the synthetic SL GR24. SMAX1 and SMXL2 transcripts are reduced in max2 seedlings, which could indicate negative feedback regulation by KAR/SL signaling. smax1 seed and seedling growth mimics the wild type treated with KAR/SL, but smax1 seedlings are still responsive to 2H-furo[2,3-c]pyran-2-one (KAR2) or GR24. We conclude that SMAX1 is an important component of KAR/SL signaling during seed germination and seedling growth but is not necessary for all MAX2-dependent responses. We hypothesize that one or more SMXL proteins may also act downstream of MAX2 to control the diverse developmental responses to KARs and SLs.
Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/crescimento & desenvolvimento , Germinação/genética , Peptídeos e Proteínas de Sinalização Intracelular/fisiologia , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulação da Expressão Gênica de Plantas , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Fenótipo , Filogenia , Plântula/genética , Plântula/crescimento & desenvolvimentoRESUMO
We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB null mutant but does not appear in a phyA null mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/citologia , Arabidopsis/fisiologia , Cloroplastos/fisiologia , Fosfoproteínas/metabolismo , Folhas de Planta/fisiologia , Alanina/genética , Substituição de Aminoácidos , Proteínas de Arabidopsis/genética , Cisteína/genética , Escuridão , Regulação da Expressão Gênica de Plantas , Luz , Fosfoproteínas/genética , Fitocromo A/metabolismo , Fitocromo B/metabolismo , Folhas de Planta/citologia , Plantas Geneticamente Modificadas/fisiologia , Proteínas Serina-Treonina Quinases , Estrutura Terciária de ProteínaRESUMO
Phototropins (phot) sense blue light through the two N-terminal chromophore binding LOV domains and activate the C-terminal kinase domain. The resulting phototropin autophosphorylation is essential for biological activity. We identified the A1 subunit of Ser/Thr protein phosphatase 2A (PP2A) as interacting with full-length phot2 in yeast and also interacting with phot2 in an in vitro protein binding assay. Phenotypic characterizations of a phot1-5 rcn1-1 (for root curling in n-naphthylphthalamic acid1) double mutant, in which phot2 is the only functional phototropin and PP2A activity is reduced, showed enhanced phototropic sensitivity and enhanced blue light-induced stomatal opening, suggesting that PP2A activity is involved in regulating phot2 function. When treated with cantharidin, a chemical inhibitor of PP2A, the phot1-5 mutant exhibited enhanced phot2-mediated phototropic responses like those of the phot1-5 rcn1-1 double mutant. Immunoblot analysis to examine phot2 endogenous phosphorylation levels and in vitro phosphorylation assays of phot2 extracted from plants during dark recovery from blue light exposure confirmed that phot2 is more slowly dephosphorylated in the reduced PP2A activity background than in the wild-type PP2A background, suggesting that phosphorylated phot2 is a substrate of PP2A activity. While reduced PP2A activity enhanced the activity of phot2, it did not enhance either phot1 dephosphorylation or the activity of phot1 in mediating phototropism or stomatal opening.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Luz , Mutação , FosforilaçãoRESUMO
In roots, the "hidden half" of all land plants, gravity is an important signal that determines the direction of growth in the soil. Hence, positive gravitropism has been studied in detail. However, since the 19th century, the response of roots toward unilateral light has also been analyzed. Based on studies on white mustard (Sinapis alba) seedlings, botanists have concluded that all roots are negatively phototropic. This "Sinapis-dogma" was refuted in a seminal study on root phototropism published a century ago, where it was shown that less then half of the 166 plant species investigated behave like S. alba, whereas 53% displayed no phototropic response at all. Here we summarize the history of research on root phototropism, discuss this phenomenon with reference to unpublished data on garden cress (Lepidium sativum) seedlings, and describe the effects of blue light on the negative bending response in Thale cress (Arabidopsis thaliana). The ecological significance of root phototropism is discussed and the relationships between gravi- and phototropism are outlined, with respect to the starch-statolith-theory of gravity perception. Finally, we present an integrative model of gravi- and blue light perception in the root tip of Arabidopsis seedlings. This hypothesis is based on our current view of the starch-statolith-concept and light sensing via the cytoplasmic red/blue light photoreceptor phytochrome A and the plasma membrane-associated blue light receptor phototropin-1. Open questions and possible research agendas for the future are summarized.
Assuntos
Gravitropismo/efeitos da radiação , Luz , Fototropismo/fisiologia , Fototropismo/efeitos da radiação , Raízes de Plantas/fisiologia , Raízes de Plantas/efeitos da radiação , Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Gravitropismo/fisiologiaRESUMO
Adaptation to seasonal change is a crucial component of an organism's survival strategy. To monitor seasonal variation, organisms have developed the capacity to measure day length (photoperiodism). Day-length assessment involves the photoperiodic control of flowering in Arabidopsis thaliana, whereby the coincidence of light and high expression of CONSTANS (CO) induces the expression of FLOWERING LOCUS T (FT), leading to flowering in long-day conditions. Although controlling CO expression is clearly a key step in day-length discrimination, the mechanism that generates day-length-dependent CO expression remains unknown. Here we show that the clock-controlled FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) protein has an essential role in generating the diurnal CO peak and that this function is dependent on light. We show that a recombinant FKF1 LIGHT, OXYGEN OR VOLTAGE (LOV) domain binds the chromophore flavin mononucleotide and undergoes light-induced photochemistry, indicating that FKF1 may function as a photoperiodic blue-light receptor. It is likely that the circadian control of FKF1 expression and the light regulation of FKF1 function coincide to control the daytime CO waveform precisely, which in turn is crucial for day-length discrimination by Arabidopsis.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Luz , Fotoperíodo , Transdução de Sinais , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Ritmo Circadiano , Cor , Proteínas de Ligação a DNA/genética , Flores/genética , Flores/fisiologia , Regulação da Expressão Gênica de Plantas , Genes de Plantas/genética , Estrutura Terciária de Proteína , Estações do Ano , Fatores de Tempo , Fatores de Transcrição/genéticaRESUMO
Blue and ultraviolet-A light regulate a wide range of responses in plants, including phototropism, chloroplast migration and stomatal opening. However, the photoreceptors for these light responses have been identified only recently. The phototropins (phot1 and phot2) represent a new class of receptor kinases that appear to be exclusive to plants. Recent genetic analysis has shown that phot1 and phot2 exhibit partially overlapping functions in mediating phototropism, chloroplast migration, and stomatal opening in Arabidopsis. Although significant progress has been made in understanding the early photochemical and biochemical events that follow phototropin excitation, the details of how this excitation activates such different responses remain to be elucidated.
Assuntos
Proteínas de Drosophila , Proteínas do Olho , Flavoproteínas/fisiologia , Células Fotorreceptoras de Invertebrados , Plantas/efeitos da radiação , Arabidopsis/genética , Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/fisiologia , Cloroplastos/fisiologia , Criptocromos , Flavoproteínas/química , Flavoproteínas/genética , Luz , Mutação , Oxigênio/fisiologia , Fosfoproteínas/química , Fosfoproteínas/genética , Fosfoproteínas/fisiologia , Fototropismo/fisiologia , Fototropismo/efeitos da radiação , Plantas/genética , Plantas/metabolismo , Proteínas Serina-Treonina Quinases , Receptores Acoplados a Proteínas G , Espectrofotometria , Raios UltravioletaRESUMO
The resistance encountered by a seedling as it pushes through the soil causes inhibition of stem elongation and stimulates stem thickening, facilitating soil penetration. A new study demonstrates that two proteolytic pathways work in double-negative fashion - one targeting the other - to protect transcription factors central to this response.
Assuntos
Plântula , Solo , PlantasRESUMO
Brucella is the causative agent of the zoonotic disease brucellosis, and its success as an intracellular pathogen relies on its ability to adapt to the harsh environmental conditions that it encounters inside the host. The Brucella genome encodes a sensor histidine kinase containing a LOV domain upstream from the kinase, LOVHK, which plays an important role in light-regulated Brucella virulence. In this report we study the intracellular signaling pathway initiated by the light sensor LOVHK using an integrated biochemical and genetic approach. From results of bacterial two-hybrid assays and phosphotransfer experiments we demonstrate that LOVHK functionally interacts with two response regulators: PhyR and LovR, constituting a functional two-component signal-transduction system. LOVHK contributes to the activation of the General Stress Response (GSR) system in Brucella via PhyR, while LovR is proposed to be a phosphate-sink for LOVHK, decreasing its phosphorylation state. We also show that in the absence of LOVHK the expression of the virB operon is down-regulated. In conclusion, our results suggest that LOVHK positively regulates the GSR system in vivo, and has an effect on the expression of the virB operon. The proposed regulatory network suggests a similar role for LOVHK in other microorganisms.
Assuntos
Brucella abortus/genética , Genes Bacterianos , Óperon , Proteínas Quinases/metabolismo , Estresse Fisiológico , Brucella abortus/enzimologia , Histidina Quinase , RNA Bacteriano/isolamento & purificação , Técnicas do Sistema de Duplo-HíbridoRESUMO
Light-induced phosphorylation of a 114 kDa protein in plasma membranes isolated from the tips of maize coleoptiles was investigated in the presence of several thiol reagents at the concentration of 1 mM. Dark phosphorylation of the protein was not affected but light-induced phosphorylation was inhibited 50% with iodoacetamide, 75% with N-ethylmaleimide and 93% with N-phenylmaleimide. Previous incubation of the inhibitors with mercaptoethanol abolished the inhibitory activity completely. N-phenyl-maleimide showed the same inhibition whether it was applied before or after irradiation of the sample. Involvement of thiol group(s) in processes after photoexcitation is discussed.
Assuntos
Proteínas de Membrana/metabolismo , Reagentes de Sulfidrila/farmacologia , Zea mays/metabolismo , Membrana Celular/metabolismo , Cotilédone , Escuridão , Eletroforese em Gel de Poliacrilamida , Etilmaleimida/farmacologia , Iodoacetamida/farmacologia , Luz , Maleimidas/farmacologia , Proteínas de Membrana/isolamento & purificação , Proteínas de Membrana/efeitos da radiação , Peso Molecular , FosforilaçãoRESUMO
Reorganization of the cortical microtubule cytoskeleton is critical for guard cell function. Here, we investigate how environmental and hormonal signals cause these rearrangements and find that COP1, a RING-finger-type ubiquitin E3 ligase, is required for degradation of tubulin, likely by the 26S proteasome. This degradation is required for stomatal closing. In addition to regulating the cytoskeleton, we show that cop1 mutation impaired the activity of S-type anion channels, which are critical for stomatal closure. Thus, COP1 is revealed as a potential coordinator of cytoskeletal and electrophysiological activities required for guard cell function.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/citologia , Arabidopsis/fisiologia , Fenômenos Eletrofisiológicos , Microtúbulos/metabolismo , Estômatos de Plantas/anatomia & histologia , Ubiquitina-Proteína Ligases/metabolismo , Ácido Abscísico/farmacologia , Arabidopsis/efeitos dos fármacos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Cálcio/metabolismo , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Microtúbulos/efeitos dos fármacos , Imagem Molecular , Mutação , Estômatos de Plantas/efeitos dos fármacos , Proteólise/efeitos dos fármacos , Ubiquitina-Proteína Ligases/genéticaRESUMO
Radially arranged cortical microtubules are a prominent feature of guard cells. We observed guard cells expressing GFP-tubulin (GFP-TUA6) with confocal microscopy and found recognizable changes in the appearance of microtubules when stomata open or close (Eisinger et al., 2012). In the present study, analysis of fluorescence distribution showed a dramatic increase in peak intensities of microtubule bundles within guard cells as stomata open. This increase was correlated with an increase in the total fluorescence that could be attributed to polymerized tubulin. Adjacent pavement cells did not show similar changes in peak intensities or integrated fluorescence when stomatal apertures changed. Imaging of RFP-tagged end binding protein 1 (EB1) and YFP-tagged α-tubulin expressed in the same cell revealed that the number of microtubules with growing ends remained constant, although the total amount of polymerized tubulin was higher in open than in closed guard cells. Taken together, these results indicate that the changes in microtubule array organization that are correlated with and required for normal guard cell function are characterized by changes in microtubule clustering or bundling.
Assuntos
Arabidopsis/citologia , Arabidopsis/fisiologia , Microtúbulos/metabolismo , Estômatos de Plantas/citologia , Estômatos de Plantas/fisiologia , Proteínas de Arabidopsis/metabolismo , Escuridão , Fluorescência , Proteínas de Fluorescência Verde/metabolismo , Imageamento Tridimensional , Proteínas Recombinantes de Fusão/metabolismo , Transdução de Sinais , Tubulina (Proteína)/metabolismoRESUMO
The author describes the somewhat convoluted pathway he followed from amateur taxonomy of Minnesota wildflowers to identification of the phototropin family of blue-light receptors. He also mentions individuals who were important in moving his career first into plant taxonomy, then plant development, and finally plant photobiology (and out of music). He emphasizes the many twists and turns a research career can take, including a few that lead to blind ends. He also emphasizes the oscillatory nature of his career-back and forth between the Atlantic and Pacific oceans (with occasional forays to Freiburg, Germany) and back and forth between red-light receptors and blue-light receptors. There is a short intermission in which he describes his longtime relationship with California's Henry W. Coe State Park. Finally, he relates how he followed the unlikely pathway from plant blue-light receptors to a blue-light receptor required to maximize virulence of a bacterial animal pathogen.
Assuntos
Bacteriologia/história , Botânica/história , Bactérias/patogenicidade , História do Século XX , Minnesota , Fototropinas/fisiologia , PlantasRESUMO
Bacteria rely on two-component signaling systems in their adaptive responses to environmental changes. Typically, the two-component system consists of a sensory histidine kinase that signals by transferring a phosphoryl group to a secondary response regulator that ultimately relays the signal to the cell. Some of these sensors use PAS (Per-Arnt-Sin) domains. A new member of the PAS super family is the LOV (light, oxygen, voltage) domain, a 10-kDa flavoprotein that functions as a light-sensory module in plant, algal, fungal, and bacterial blue-light receptors. Putative LOV domains have been identified in the genomes of many higher and lower eukaryotes, plants, eubacteria, archaebacteria, and particularly in genes coding for histidine kinases (LOV-histidine kinases, LOV-HKs) of plant and animal pathogenic bacteria, including Brucella. We describe here biochemical, photochemical, and biophysical methodology to purify these enzymes and to characterize their light-activation process.