Biological Sciences
Phytochromes
Phytochromes are photoreceptors found in plants that are sensitive to red and far-red light. They play a crucial role in regulating various plant processes, including seed germination, seedling development, and flowering. Phytochromes exist in two interconvertible forms, Pr (red light-absorbing) and Pfr (far-red light-absorbing), and their ratio in the plant determines the plant's response to light.
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10 Key excerpts on "Phytochromes"
- Axel Griesbeck, Michael Oelgemöller, Francesco Ghetti(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
1225 52.1 Introduction Phytochromes are photoreceptors that regulate many aspects of plant growth and development in response to red/far-red light signals from the environment. 1–3 Phytochromes in higher plants are encoded by small gene families. 4 For example, the completed whole genome sequences of Arabidopsis thaliana and Oryza sativa Phytochromes reveal five ( PHYA to PHYE ) and three ( PHYA to PHYC ) genes, respec-tively. 5,6 Phytochromes are dimeric chromoproteins having covalently linked open tetrapyrrole phyto-chromobilin and exist in two photochromic species, red-light-absorbing Pr and far-red-light-absorbing Pfr forms. They are biosynthesized as the Pr form in the dark, which can be phototransformed into the Pfr form upon exposure to red light. The Pr-to-Pfr phototransformation of Phytochromes induces the highly regulated signaling network for photomorphogenesis in plants. 7–9 Recent studies on the molecu-lar mechanisms of the phytochrome-mediated light signaling reveal that phytochrome photoactivation impacts on the control of protein subcellular localization, 10,11 transcription, 12,13 protein stability, 14,15 and protein phosphorylation. 16 Here, we highlight the current knowledge about the molecular mechanisms of phytochrome function based on the recent advances. 52 Phytochrome: Molecular Mechanisms for Light Signaling in Plants 52.1 Introduction .................................................................................... 1225 52.2 Domain Structure of Phytochrome ............................................. 1226 52.3 Conformational Changes during Photoactivation .................... 1227 52.4 Molecular Mechanisms of Phytochrome Signaling ..................
eBook - PDF- Shain-dow Kung, Shang-fa Yang(Authors)
- 1998(Publication Date)
- World Scientific(Publisher)
Chapter 8 Discovery of Phytochrome Winslow R. Briggs Department of Plant Biology, Carnegie Institution of Washington 260 Panama Street, Stanford, California 94305, USA ABSTRACT Independent studies of flowering and seed germination carried out early in the twentieth century converged at mid-century to show that both flowering and seed germination were controlled by a photoreceptor that was converted to a biologically active form by red light and converted back to a biologically inactive form by far red light. Various vegetative effects such as stem elongation and leaf expansion were also shown to be regulated by this pigment. By 1959, a pigment matching the predicted properties for the hypothesized photoreversible photoreceptor was detected, and named phytochrome a year later. Subsequent research showed that there is in fact a family of Phytochromes playing a range of roles in plant development. Most of the seminal research were carried out at various laboratories at the United States Department of Agriculture facility at Beltsville, Maryland, and represent some of the greatest accomplishments by that agency. Introduction Unlike most animals, plants do not have a convenient short-term mechanism for escaping an unfavorable environment. Anchored to the soil or some other substrate, they have no opportunity to escape to a more benign and protective world when conditions around them turn unpleasant. As a consequence, they have evolved a remarkable series of signal transduction pathways that enable them to respond to environmental signals. Although factors such as nutrient availability, temperature, and moisture all can have important signaling roles, it is light that provides the broadest ranges of signals. Indeed responsiveness to light is essential for optimization of photosynthesis among other things.
eBook - PDF- Alfred Batschauer, Donat-P Hader, Giulio Jori(Authors)
- 2007(Publication Date)
- Royal Society of Chemistry(Publisher)
. . . . . . . . . . . . . . . . . . . . . . 197 182 F. NAGY, E. KEVEI, K. HARTER AND E. SCHÄFER Abstract The family of phytochrome photoreceptors regulates growth and development throughout the entire life cycle of higher plants. The molecular mechanism by which the light signal is converted into a regulatory signal for gene expression is the subject of intensive research. During the past two years genetic, bioche-mical and cell biological studies have provided novel observations and changed our view of the phytochrome-initiated signalling cascades. It became evident that the light quality- and quantity-dependent regulation of the nucleo-cytoplasmic partitioning of Phytochromes and their conformation-dependent, functional interaction with transcription factors inside the cytoplasm and the nucleus are important components of phototransduction. To understand specificity, temporal and spatial differences between the various phytochrome-controlled responses it will be essential to unravel the molecular mechanisms (import/export/degradation) that ensure controlled compartmentalization of these photoreceptors. 6.1 Introduction 6.1.1 Plants and light Plants as sessile organisms have to cope with changing environmental con-ditions at the place where they grow. To regulate their fitness and adapt to unfavourable conditions, plants depend upon reliable information about environmental factors such as temperature, water, nutrient supply and light. Among these environmental parameters light is obviously the most important external factor for plants. Light not only serves as the source of energy for photosynthesis, but also functions as a morphogenic signal. Light regulates a wide range of developmental processes and adaptations during the entire life cycle.
eBook - PDF- Indra Vasil(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The phytochrome system is the best characterized of the two photore-ceptors, having been shown to play a critical role in regulating plant growth and development throughout the organism's life cycle. Phytochrome in higher plants is a soluble chromoprotein made up of two identical subunits with molecular masses ranging from 120 to 128 kD (Vierstra et ai, 1984). Each subunit consists of a linear tetrapyrrole chromophore covalently bound to the polypeptide via a thioether link-age (Rudiger and Scheer, 1983). The photoreceptor exists in two spec-trally distinct forms: the Pr form, which absorbs maximally in the red (Xmax. = 666 nm) region of the spectrum, and the Pfr form, which ab-sorbs maximally in the far-red (Xmax. = 730 nm) region of the spectrum. The two forms are reversibly interconvertible by light: Pr is converted to Pfr by absorbing red light and Pfr is converted to Pr by absorbing far-red light. In vivo, photoconversion of Pr to Pfr by red light induces a vast array of morphogenic responses whereas reconversion of Pfr to Pr by far-red light cancels the induction of these responses (Lagarias, 1985). It is this property of indefinitely repeatable photointerconvertibility that allows phytochrome to funtion in its regulatory role with Pr and Pfr considered to be the inactive and active forms of the molecule, respec-tively. In essence, phytochrome can be considered to function as a bio-logical switch that can be turned on and off by light, providing a unique opportunity to influence and study a complex developmental system in a noninvasive manner. Historically, it has long been known that the germination of many types of seed is affected by light. The germination of Grand Rapids let-tuce seeds was shown to be promoted by red light and inhibited by far-red light (Flint and McAlister, 1937).
eBook - PDFSustainable Agriculture
Nanotechnology and Biotechnology for Crop Production and Protection
- Vishnu D. Rajput, Abhishek Singh, Karen Ghazaryan, Tatiana M. Minkina, Abdel Rahman M. Al-Tawaha(Authors)
- 2024(Publication Date)
- De Gruyter(Publisher)
chromophore. The presence of discrete photoreceptor groups offers potential for se- lectively stimulating specific pathways, thereby exerting precise control over plant de- velopment [6]. 22.2.1 Phytochromes (PHYs) Photosensitive pigments, known as Phytochromes (PHYs), are a class of proteins that exhibit solubility. These proteins possess the ability to bind to chromophores called phytochromobilins (Fig. 22.1). By doing so, they are capable of absorbing light in the red (R) and FR regions of the electromagnetic spectrum. The absorption of R and FR light by PHYs plays a crucial role in various light-mediated responses exhibited by plants. In vivo, light undergoes a conversion process in which it transforms PHYs into two photoreversible forms. One form, known as Pr, absorbs R light and exhibits an absorption peak within the range of 650–670 nm. The other form, known as Pfr, ab- sorbs FR light and exhibits an absorption peak within the range of 705–740 nm. The process of photoreception involves the absorption of red light by the pigment Pr, which subsequently undergoes conversion into its active form, Pfr. Conversely, the pigment Pfr absorbs FR light and undergoes conversion into its inert form, Pr. PHYs move from the cytoplasm to the nucleus in their active forms in order to modulate the expression of various genes associated with photomorphogenic responses [7]. The photoequilibrium of PHYs at the plant level, denoted as PPE, can be calcu- lated using the formula PPE = Pfr/(Pr + Pfr). This photoequilibrium is significantly influenced by the ratio of red to far red (R:FR) light in the incident light. The spectral makeup of incident light undergoes changes throughout the course of the day, result- ing in a coherent variation in R:FR ratio from 1.15 to 0.70 [8]. The value of Pfr:Pr ratio, as well as its associated value, decreases gradually along the plant canopy, from the uppermost part to the lower part.
eBook - PDFPlants and Microclimate
A Quantitative Approach to Environmental Plant Physiology
- Hamlyn G. Jones(Author)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
Some lower plants also have a photoreceptor (neochrome) that includes both phototropin and phytochrome domains. 8.2.3 Phytochrome Phytochrome has been known since the 1950s but it is only recently that the complexity of the phytochrome signalling system in plants has become clear. Not only are there at least five distinct phytochrome 8.2 Detection of the signal 209 molecules that participate in regulation of different photomorphogenic events, but there is also a series of complex downstream signalling pathways, which is only now beginning to be understood (Chen & Chory, 2011). Phytochromes use a linear tetrapyrrole bilin chromophore to sense the ratio of red light (R) to far-red light (FR) and are apparently unique among higher plant photoreceptors in that they can exist in two photo-interconvertible forms: a red-light absorbing form (Pr) that has an absorption maximum in the red (660 nm) and a far-red absorbing form (Pfr) that has an absorption maximum in the far-red (730 nm). It is in this region of the spectrum that natural radiation shows the greatest variation so phytochrome is perhaps well fitted as a detector of the spectral quality of incident radiation and is therefore involved in morphogenetic responses such as shade avoidance or the initiation of growth on exposure to light. Absorption spectra of Pr and Pfr are illustrated in Figure 2.4 (along with the absorption spectra of riboflavin and chlorophyll). Phytochromes are synthesised as the biologically inactive (at least in plants) Pr form. Biological action is inititated by photoconversion to the far-red absorbing Pfr form; this triggers rapid (within minutes) translocation of phytochrome into the nucleus where the activated photoreceptor interacts with a family of transcription factors (the phytochrome interacting factors, or PIFs) and initiates a cascade of changes in gene expression that themselves are detectable within minutes.
eBook - ePub- Heinz Dürr, Henri Bouas-Laurent(Authors)
- 2003(Publication Date)
- Elsevier Science(Publisher)
Chapter 19Phytochrome
S.E. Braslavsky1 INTRODUCTION
Biological photoreceptors have been classified as either light transducers (photosensors or photoperceptors), sensing the quality and quantity of radiation, or as energy converters. Among the first there are (a) different molecular species triggering photomovement at various levels, e. g., movement of motile organisms, intracellular movement, and movement of plant organs in higher plants (ref. 1 ), (b) phytochrome, various blue light/UV-A (320–400 nm) and UV-B (280–320 nm) photoreceptors (ref. 2 ), all of which control to different degrees plant growth and development, and (c) the visual pigments, in particular rhodopsin in vertebrates and various types of pigments in invertebrates (ref. 3 ). Among the energy converters we find bacteriorhodopsin and the protein complexes of the chlorophylls and of bacteriochlorophyll. In addition, the antenna pigments (accesory pigments), like e. g., phycocyanin, phycoerythrin, allophycocyanin, serve to transfer the energy of the absorbed light to the reaction center in algae.Most biological photoreceptor systems are photochromic, i. e., after performing the photochemically triggered reaction, the system is somehow restored to its initial state and is ready to absorb another quantum of radiation in order to photoinitiate again the specific function. Few of these pigments remain photochromic when isolated from the living complex system of which they are part. This is the case for phytochrome. I will concentrate the discussion on this pigment. It has two stable forms that are transformed into each other by light of appropriate wavelength and it does not need an additional partner in order to complete the photochromic cycle.Some years ago Max Delbrück proposed a general concept marking the difference between the light-transducer and the energy-converter photoreceptors. In the former, after the absorption of radiation a flexible chromophore would lead to protein conformational changes inducing this way the transmission of a signal. Alternatively, a rigidly attached chromophore would only lead to charge separation in the energy converters or to energy transfer in the accessory antenna pigments (ref. 4
eBook - PDF- Gurnah, Akinloye(Authors)
- 2018(Publication Date)
- Agri Horti Press(Publisher)
There are two spectrally distinct forms of Phytochromes, a R (660 nm) absorbing form (Pr) and a FR (730 nm) absorbing form (Pfr). The molecular mechanism for the on/off switching of the Phytochromes is driven by the photochromic phototrans-formation between the two forms. The photo-activated Pfr signals are transduced by interacting with a wide array of downstream signalling components and finally regulate genes involved in photomorphogenesis and photosynthesis. The phytochrome molecule consists of two structural domains, the globular N-terminal chromophore-binding domain (<“65 kDa) and the conformationally open or extended Cterminal domain (<“55 kDa). The two domains are connected via a flexible hinge region. The N-terminal domain is necessary and sufficient for photoperception and possesses the bilin lyase domain (BLD) which allows the attachment of the chromophore to apo-phytochrome. Yeast two-hybrid screenings with a C-terminal segment as bait have revealed that the Cterminal domain interacts with the downstream phytochromeinteracting proteins (PIPs), such as phytochrome-interacting factor-3 This ebook is exclusively for this university only. Cannot be resold/distributed. Biosynthesis of Phytochrome: Determining Photoperiods of Plants 273 (PIF3), nucleoside diphosphate kinase-2 (NDPK2), phytochrome kinase substrate-1 (PKS1), cryptochromes, FyPP (flower specific, phytochrome associated protein phosphatase 2A), PIF4, PIF1/PIL5, EARLY FLOWERING 3 (ELF3), ZEITLUPE (ZTL), ADAGIO1 (Ado1), and so on. Another phytochrome-interacting protein, ARR4 is known to bind the N-terminal domain of Phytochromes. Interestingly, PIF3 apparently interacts with both C- and N-terminal domains. Several conserved subdomains and sequence motifs have been identified in the phytochrome molecules. In the Nterminal light-sensing domain, there are four subdomains: P1 (N-terminal extension, NTE), P2, P3 (bilin lyase domain, BLD), P4 (phytochrome domain, PHY).
eBook - PDF- Pandey, Narendra Shankar(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
Epigenetic changes of gene expression in many organisms, from yeast to mammals, often require cell division and DNA replication, as is the case for vernalization. The involvement of epigenetic regulation in the vernalization process has been confrmed in the LDP Arabidopsis. 8.10. Phytochrome Phytochrome, a blue protein pigment with a molecular mass of about 125 kDa (kilodaltons). Phytochrome can interconvert between Pr and Pfr Forms -This ebook is exclusively for this university only. Cannot be resold/distributed. In dark-grown or etiolated plants, phytochrome is present in a red light– absorbing form, referred to as Pr because it is synthesized in this form. Pr, is converted by red light to a far-red light–absorbing form called Pfr, which is blue-green. Pfr, in turn, can be converted back to Pr by far-red light. Known as photoreversibility, this conversion/ reconversion property is the most distinctive property of phytochrome. The interconversion of the Pr and Pfr forms can be measured in vivo or in vitro. In fact, most of the spectral properties of carefully purifed phytochrome measured in vitro are the same as those observed in vivo. When Pr molecules are exposed to red light, most of them absorb it and are converted to Pfr, but some of the Pfr also absorbs the red light and is converted back to Pr because both Pr and Pfr absorb red light (Figure - 8.9). Thus the proportion of phytochrome in the Pfr form after saturating irradiation by red light is only about 85 per cent. Similarly, the very small amount of far-red light absorbed by Pr makes it impossible to convert Pfr entirely to Pr by broadspectrum far-red light. Instead, an equilibrium of 97 per cent Pr and 3 per cent Pfr is achieved. This equilibrium is termed the photostationary state. In addition to absorbing red light, both forms of phytochrome absorb light in the blue region of the spectrum.
eBook - PDF- Winslow R. Briggs, John L. Spudich, Winslow R. Briggs, John L. Spudich(Authors)
- 2006(Publication Date)
- Wiley-VCH(Publisher)
Only two of these genes for which cryp- tochromes play a major role in regulation will be considered here for further discus- sion, the nuclear encoded chalcone synthase (CHS) and the plastid encoded psbD gene encoding the D2 protein of photosystem II. Chalcone synthase (CHS) is the first enzyme of the f lavonoid and anthocyanin pathway. Flavonoids and anthocyanins serve many functions such as repellents of plant pathogens and herbivores, phytoalexins, mediators in plant-microbe interac- tion, and UV-protectants (Harbourne, 1993; Koes et al., 1994; Shirley, 1996). The red and purple anthocyanins may serve as sunscreens for etiolated seedlings to protect them against light damage as long as the photosynthetic apparatus is not completely assembled. According to their multiple functions, the synthesis of these compounds is strongly enhanced by environmental factors such as cold stress, pathogen attack, and light. Here, we will focus on the light-regulation of anthocyanin formation in Arabidopsis and Sinapis seedlings and how this regulation is mediated by differential expression of CHS. 10 Plant Cryptochromes: Their Genes, Biochemistry, and Physiological Roles 229 Arabidopsis contains a single CHS gene (Feinbaum and Ausubel, 1988) that is strongly induced by UV-A, white, and blue light but only weakly by red light (Fein- baum et al., 1991). This result indicates that expression of this gene is primarily un- der control of a UV-A/blue-light receptor and that phytochrome(s) play only a minor role in up-regulating this gene. However, continuous far-red light acting on phyA al- so enhances CHS expression in etiolated Arabidopsis and Sinapis seedlings (Batschauer et al., 1991; Kaiser et al., 1995; Kunkel et al., 1996). The major role of cry1 in regulating CHS expression under blue-light was confirmed by analyzing the cry1 (hy4) mutant.
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