Plant Photoreceptors Research Articles

An overview of phytochrome: An important light switch and photo-sensory antenna for regulation of vital functioning of plants

AbstractPlants are the primary source of nutrition and essential to maintain life on earth. They have evolved very delicate and advanced photo-sensory antennae to sense their outer environment and transduce the received information for their growth and development accordingly. This “light switch” phenomenon of plants has slowly being unraveled and various plant photoreceptors, their role in downstream molecular signaling, mutual interaction, response to circadian cycle and light signals have been discovered. The photosensory antennae in plants; phytochromes, cryptochromes and phototropins play a very crucial role in sensing the ambient light intensities. By direct interaction with the environment through these photosensory antennae, plants shift their homeostasis to regulate their growth and development. The phytochrome light receptors of plants are responsive to R/FR light and by inducing signaling pathways, trigger the physiological responses such as germination and flowering. The phytochromes also directly contribute to plant development by affecting its photosynthetic rate. To elucidate the role of phytochromes in plant metabolism, this review will focus on the importance of phytochromes, their mechanism of action and their application as an emerging field in plant biology.

Optogenetic control of endogenous Ca(2+) channels in vivo.

Calcium (Ca(2+)) signals that are precisely modulated in space and time mediate a myriad of cellular processes, including contraction, excitation, growth, differentiation and apoptosis. However, study of Ca(2+) responses has been hampered by technological limitations of existing Ca(2+)-modulating tools. Here we present OptoSTIM1, an optogenetic tool for manipulating intracellular Ca(2+) levels through activation of Ca(2+)-selective endogenous Ca(2+) release-activated Ca(2+) (CRAC) channels. Using OptoSTIM1, which combines a plant photoreceptor and the CRAC channel regulator STIM1 (ref. 4), we quantitatively and qualitatively controlled intracellular Ca(2+) levels in various biological systems, including zebrafish embryos and human embryonic stem cells. We demonstrate that activating OptoSTIM1 in the CA1 hippocampal region of mice selectively reinforced contextual memory formation. The broad utility of OptoSTIM1 will expand our mechanistic understanding of numerous Ca(2+)-associated processes and facilitate screening for drug candidates that antagonize Ca(2+) signals.

Blue Wavelengths from LED Lighting Increase Nutritionally Important Metabolites in Specialty Crops

Light is one of the most important environmental stimuli impacting plant growth and development. Plants have evolved specialized pigment-protein complexes, commonly referred to as photoreceptors, to capture light energy to drive photosynthetic processes, as well as to respond to changes in light quality and quantity. Blue light can act as a powerful environmental signal regulating phototropisms, suppression of stem elongation, chloroplast movements, stomatal regulation, and cell membrane transport activity. An emerging application of light-emitting diode (LED) technology is for horticultural plant production in controlled environments. Work by our research group is measuring important plant responses to different wavelengths of light from LEDs. We have demonstrated positive impacts of blue wavelengths on primary and secondary metabolism in microgreen and baby leafy green brassica crops. Results show significant increases in shoot tissue pigments, glucosinolates, and essential mineral elements following exposure to higher percentages of blue wavelengths from LED lighting. The perception of energy-rich blue light by specialized plant photoreceptors appears to trigger a cascade of metabolic responses, which is supported by current research showing stimulation of primary and secondary metabolite biosynthesis following exposure to blue wavelengths. Management of the light environment may be a viable means to improve concentrations of nutritionally important primary and secondary metabolites in specialty vegetable crops.

A proteome map of a quadruple photoreceptor mutant sustains its severe photosynthetic deficient phenotype

Light is the environmental factor that most affects plant growth and development through its impact on photomorphogenesis and photosynthesis. A quadruple photoreceptor mutant lacking four of the most important photoreceptors in plants, phytochromes A and B (phyA, phyB) and cryptochromes 1 and 2 (cry1, cry2), is severely affected in terms of growth and development. Previous studies have suggested that in addition to a photomorphogenic disorder, the phyA phyB cry1 cry2 quadruple mutant might have severe alterations in photosynthetic ability. Here, we investigated the photosynthetic processes altered in the quadruple mutant and performed a proteomic profiling approach to identify some of the proteins involved. The phyA phyB cry1 cry2 quadruple mutant showed reduced leaf area and total chlorophyll content. Photosynthetic rates at high irradiances were reduced approximately 65% compared to the wild type (WT). Light-saturated photosynthesis and the response of net CO2 exchange to low and high internal CO2 concentrations suggest that the levels or activity of the components of the Calvin cycle and electron transport might be reduced in the quadruple mutant. Most of the under-expressed proteins in the phyA phyB cry1 cry2 quadruple mutant consistently showed a chloroplastic localization, whereas components of the Calvin cycle and light reaction centers were overrepresented. Additionally, Rubisco expression was reduced threefold in the phyA phyB cry1 cry2 quadruple mutant.Together, these results highlight the importance of the phytochrome and cryptochrome families in proper autotrophy establishment in plants. They also suggest that an overall limitation in the chlorophyll levels, expression of Rubisco, and enzymes of the Calvin Cycle and electron transport that affect ribulose-1,5-biphosphate (RuBP) regeneration reduced photosynthetic capacity in the phyA phyB cry1 cry2 quadruple mutant.

How Does Photoreceptor UVR8 Perceive a UV-B Signal?

UVR8 is the only known plant photoreceptor that mediates light responses to UV-B (280-315nm) of the solar spectrum. UVR8 perceives a UV-B signal via light-induced dimer dissociation, which triggers a wide range of cellular responses involved in photomorphogenesis and photoprotection. Two recent crystal structures of Arabidopsis thaliana UVR8 (AtUVR8) have revealed unusual clustering of UV-B-absorbing Trp pigments at the dimer interface and provided a structural framework for further mechanistic investigation. This review summarizes recent advances in spectroscopic, computational and crystallographic studies on UVR8 that are directed toward full understanding of UV-B perception at the molecular level.

Photoinduced transformation of UVR8 monitored by vibrational and fluorescence spectroscopy.

Tryptophan residues at the dimer interface of the plant photoreceptor UVR8 promote monomerisation after UV-B absorption via a so far unknown mechanism. Using FTIR spectroscopy we assign light-induced structural transitions of UVR8 mainly to amino acid side chains without major transformations of the secondary structure of the physiologically relevant C-terminal extension. Additionally, we assign the monomerisation associated increase and red shift of the UVR8 tryptophan emission to a photoinduced rearrangement of tryptophan side chains and a relocation of the aspartic acid residues D96 and D107, respectively. By illumination dependent emission spectroscopy we furthermore determined the quantum yield of photoinduced monomerisation to 20 ± 8%.

Light-activated phytochrome A and B interact with members of the SPA family to promote photomorphogenesis in Arabidopsis by reorganizing the COP1/SPA complex.

Phytochromes function as red/far-red photoreceptors in plants and are essential for light-regulated growth and development. Photomorphogenesis, the developmental program in light, is the default program in seed plants. In dark-grown seedlings, photomorphogenic growth is suppressed by the action of the CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)/SUPPRESSOR OF phyA-105 (SPA) complex, which targets positive regulators of photomorphogenic growth for degradation by the proteasome. Phytochromes inhibit the COP1/SPA complex, leading to the accumulation of transcription factors promoting photomorphogenesis; yet, the mechanism by which they inactivate COP1/SPA is still unknown. Here, we show that light-activated phytochrome A (phyA) and phytochrome B (phyB) interact with SPA1 and other SPA proteins. Fluorescence resonance energy transfer-fluorescence lifetime imaging microscopy analyses show that SPAs and phytochromes colocalize and interact in nuclear bodies. Furthermore, light-activated phyA and phyB disrupt the interaction between COP1 and SPAs, resulting in reorganization of the COP1/SPA complex in planta. The light-induced stabilization of HFR1, a photomorphogenic factor targeted for degradation by COP1/SPA, correlates temporally with the accumulation of phyA in the nucleus and localization of phyA to nuclear bodies. Overall, these data provide a molecular mechanism for the inactivation of the COP1/SPA complex by phyA- and phyB-mediated light perception.

Recipient of the 2014 molecular ecology prize: Johanna Schmitt.

Recipient of the 2014 molecular ecology prize: Johanna Schmitt.

紫外光から遠赤色光まで，多様な植物光受容体

紫外光から遠赤色光まで，多様な植物光受容体

Searching for the mechanism of signalling by plant photoreceptor cryptochrome

Even though the plant photoreceptors cryptochromes were discovered more than 20years ago, the mechanism through which they transduce light signals to their partner molecules such as COP1 (Constitutive Photomorphogenic 1) or SPA1 (Suppressor of Phytochrome A) still remains to be established. We propose that a negative charge induced by light in the vicinity of the flavin chromophore initiates cryptochrome 1 signalling. This negative charge might expel the protein-bound ATP from the binding pocket, thereby pushing off the C-terminus that covers the ATP pocket in the dark state of the protein. This conformational change should allow for phosphorylation of previously inaccessible amino acids. A partially phosphorylated ‘ESSSSGRR–VPE’ fragment of the C-terminus could mimic the sequence of the transcription factor HY5 that is essential for binding to the negative regulator of photomorphogenesis COP1. HY5 release through competition for the COP1 binding site could represent the long-sought connection between light activation of cryptochrome and modulation of photomorphogenesis.

Plant Productivity: Can Photoreceptors Light the Way?

One of the crucial challenges faced by the plant research community today is in understanding the myriad processes that orchestrate growth, which is paramount to produce sufficient biomass for food and non-food applications in the future. Plant photoreceptors play important regulatory roles in developmental processes that can consequently affect productivity. The UN Food and Agriculture Organization estimates that by 2030 the world population will reach 8.3 billion. Biological approaches that can increase productivity and lower postharvest losses are thus essential for future food security. Regulating the activity of genes that can affect plant architecture, development or yield could likely be the key to increasing plant productivity. Recent advances in plant research have identified several photoreceptor genes and gene networks that play pivotal roles in these responses. The knowledge arising from such research therefore needs to be translated to the field to support programs aimed at increasing crop productivity. Given the evidence for their role in determining agricultural traits, these genes are favorably placed to become the focus of targeted breeding approaches for enhancing the agronomic value of domesticated lines.

Tissue-specific and light-dependent regulation of phytochrome gene expression in rice.

Phytochromes are red- and far red light photoreceptors in higher plants. Rice (Oryza sativa L.) has three phytochromes (phyA, phyB and phyC), which play distinct as well as cooperative roles in light perception. To gain a better understanding of individual phytochrome functions in rice, expression patterns of three phytochrome genes were characterized using promoter-GUS fusion constructs. The phytochrome genes PHYA and PHYB showed distinct patterns of tissue- and developmental stage-specific expression in rice. The PHYA promoter-GUS was expressed in all leaf tissues in etiolated seedlings, while its expression was restricted to vascular bundles in expanded leaves of light-grown seedlings. These observations suggest that light represses the expression of the PHYA gene in all cells except vascular bundle cells in rice seedlings. Red light was effective, but far red light was ineffective in gene repression, and red light-induced repression was not observed in phyB mutants. These results indicate that phyB is involved in light-dependent and tissue-specific repression of the PHYA gene in rice.

Phytochrome B Is Required for Light-Mediated Systemic Control of Stomatal Development

SummaryStomata are pores found on the surfaces of leaves, and they regulate gas exchange between the plant and the environment [1]. Stomatal development is highly plastic and is influenced by environmental signals [2]. Light stimulates stomatal development, and this response is mediated by plant photoreceptors [3–5], with the red-light photoreceptor phytochrome B (phyB) having a dominant role in white light [3]. Light also regulates stomatal development systemically, with the irradiance perceived by mature leaves modulating stomatal development in young leaves [6, 7]. Here, we show that phyB is required for this systemic response. Using a combination of tissue-specific expression and an inducible expression system in the loss-of-function phyB-9 mutant [8], we show that phyB expression in the stomatal lineage, mesophyll, and phloem is sufficient to restore wild-type stomatal development. Induction of PHYB in mature leaves also rescues stomatal development in young untreated leaves, whereas phyB mutants are defective in the systemic regulation of stomatal development. Our data show that phyB acts systemically to regulate cell fate decisions in the leaf epidermis.

The D-ring, Not the A-ring, Rotates in Synechococcus OS-B′ Phytochrome

Phytochrome photoreceptors in plants and microorganisms switch photochromically between two states, controlling numerous important biological processes. Although this phototransformation is generally considered to involve rotation of ring D of the tetrapyrrole chromophore, Ulijasz et al. (Ulijasz, A. T., Cornilescu, G., Cornilescu, C. C., Zhang, J., Rivera, M., Markley, J. L., and Vierstra, R. D. (2010) Nature 463, 250-254) proposed that the A-ring rotates instead. Here, we apply magic angle spinning NMR to the two parent states following studies of the 23-kDa GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA) domain fragment of phytochrome from Synechococcus OS-B'. Major changes occur at the A-ring covalent linkage to the protein as well as at the protein residue contact of ring D. Conserved contacts associated with the A-ring nitrogen rule out an A-ring photoflip, whereas loss of contact of the D-ring nitrogen to the protein implies movement of ring D. Although none of the methine bridges showed a chemical shift change comparable with those characteristic of the D-ring photoflip in canonical phytochromes, denaturation experiments showed conclusively that the same occurs in Synechococcus OS-B' phytochrome upon photoconversion. The results are consistent with the D-ring being strongly tilted in both states and the C15=C16 double bond undergoing a Z/E isomerization upon light absorption. More subtle changes are associated with the A-ring linkage to the protein. Our findings thus disprove A-ring rotation and are discussed in relation to the position of the D-ring, photoisomerization, and photochromicity in the phytochrome family.

2SEP-01 カラフルな植物光受容体、赤、青、UV-B を見る(生物界における光とは? : 動物・植物・微生物の光科学、そしてオプトジェネティクス,シンポジウム,第52回日本生物物理学会年会(2014年度))

2SEP-01 カラフルな植物光受容体、赤、青、UV-B を見る(生物界における光とは? : 動物・植物・微生物の光科学、そしてオプトジェネティクス,シンポジウム,第52回日本生物物理学会年会(2014年度))

Plants Sense a Blue Light Special

Plant photoreceptors cooperate to regulate transcription in response to blue light.

Seeing the unseen: How plants sense UV-B

Sunlight not only drives photosynthesis, but also provides cues to regulate plant growth and development. Termed photomorphogenesis, this ability to modulate development in response to changes in light is key to plant survival. Plants have evolved several photoreceptors to perceive and respond to different wavelengths of light found in the daylight spectrum. The majority of plant photoreceptors are proteins with a bound chromophore, a non-protein component that captures photon energy from a particular wavelength of light and converts it into a signal by inducing conformational changes in the protein itself. The resulting changes in the protein activate a signal cascade, which in turn produces alterations in gene expression, allowing the plant to adapt to the light environment. This article discusses what is known about a novel plant photoreceptor, UVR8, and the signalling pathway it activates.

LNK genes integrate light and clock signaling networks at the core of the Arabidopsis oscillator

Light signaling pathways and the circadian clock interact to help organisms synchronize physiological and developmental processes with periodic environmental cycles. The plant photoreceptors responsible for clock resetting have been characterized, but signaling components that link the photoreceptors to the clock remain to be identified. Here we describe a family of night light-inducible and clock-regulated genes (LNK) that play a key role linking light regulation of gene expression to the control of daily and seasonal rhythms in Arabidopsis thaliana. A genomewide transcriptome analysis revealed that most light-induced genes respond more strongly to light during the subjective day, which is consistent with the diurnal nature of most physiological processes in plants. However, a handful of genes, including the homologous genes LNK1 and LNK2, are more strongly induced by light in the middle of the night, when the clock is most responsive to this signal. Further analysis revealed that the morning phased LNK1 and LNK2 genes control circadian rhythms, photomorphogenic responses, and photoperiodic dependent flowering, most likely by regulating a subset of clock and flowering time genes in the afternoon. LNK1 and LNK2 themselves are directly repressed by members of the TIMING OF CAB1 EXPRESSION/PSEUDO RESPONSE REGULATOR family of core-clock genes in the afternoon and early night. Thus, LNK1 and LNK2 integrate early light signals with temporal information provided by core oscillator components to control the expression of afternoon genes, allowing plants to keep track of seasonal changes in day length.

적색광을 이용한 국화의 개화조절

BACKGROUND: The incandescent bulb and compact fluorescent lamp are widely using as a light sources for daylength extension of chrysanthemum. But, these light sources consume a lot of electricity and have short longevity. A light-emitting diode (LED) is a semi conductor light source. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime. In this study, we investigated the intensity of red light to control flowering of chrysanthemum (Dendranthema grandiflorum cv. Shinma) by using LEDs. METHODS AND RESULTS: The red (660 nm) and far-red (730 nm) light were irradiated subsequently to investigate photo-reversible flowering responses of chrysanthemum. The flowering of chrysanthemum was inhibited by night interruption with red light but subsequently irradiated far-red light induced the flowering of chrysanthemum. This photoreversibility, reversion of the inductive effect of a brief red light pulse by a subsequent far-red light pulse, is a property of photo responses regulated by the plant photoreceptor phytochrome B.

Light Regulation of Swarming Motility in Pseudomonas syringae Integrates Signaling Pathways Mediated by a Bacteriophytochrome and a LOV Protein

ABSTRACTThe biological and regulatory roles of photosensory proteins are poorly understood for nonphotosynthetic bacteria. The foliar bacterial pathogen Pseudomonas syringae has three photosensory protein-encoding genes that are predicted to encode the blue-light-sensing LOV (light, oxygen, or voltage) histidine kinase (LOV-HK) and two red/far-red-light-sensing bacteriophytochromes, BphP1 and BphP2. We provide evidence that LOV-HK and BphP1 form an integrated network that regulates swarming motility in response to multiple light wavelengths. The swarming motility of P. syringae B728a deletion mutants indicated that LOV-HK positively regulates swarming motility in response to blue light and BphP1 negatively regulates swarming motility in response to red and far-red light. BphP2 does not detectably regulate swarming motility. The histidine kinase activity of each LOV-HK and BphP1 is required for this regulation based on the loss of complementation upon mutation of residues key to their kinase activity. Surprisingly, mutants lacking both lov and bphP1 were similar in motility to a bphP1 single mutant in blue light, indicating that the loss of bphP1 is epistatic to the loss of lov and also that BphP1 unexpectedly responds to blue light. Moreover, whereas expression of bphP1 did not alter motility under blue light in a bphP1 mutant, it reduced motility in a mutant lacking lov and bphP1, demonstrating that LOV-HK positively regulates motility by suppressing negative regulation by BphP1. These results are the first to show cross talk between the LOV protein and phytochrome signaling pathways in bacteria, and the similarity of this regulatory network to that of photoreceptors in plants suggests a possible common ancestry.