Photoreceptors in Plant Photomorphogenesis to Date. Five Phytochromes, Two Cryptochromes, One Phototropin, and One Superchrome (original) (raw)
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Proceedings of the National Academy of Sciences, 1996
Plant growth and development are regulated by interactions between the environment and endogenous developmental programs. Of the various environmental factors controlling plant development, light plays an especially important role, in photosynthesis, in seasonal and diurnal time sensing, and as a cue for altering developmental pattern. Recently, several laboratories have devised a variety of genetic screens using Arabidopsis thaliana to dissect the signal transduction pathways of the various photoreceptor systems. Genetic analysis demonstrates that light responses are not simply endpoints of linear signal transduction pathways but are the result of the integration of information from a variety of photoreceptors through a complex network of interacting signaling components. These signaling components include the red/far-red light receptors, phytochromes, at least one blue light receptor, and negative regulatory genes (DET, COP, and FUS) that act downstream from the photoreceptors in the nucleus. In addition, a steroid hormone, brassinolide, also plays a role in light-regulated development and gene expression in Arabidopsis. These molecular and genetic data are allowing us to construct models of the mechanisms by which light controls development and gene expression inArabidopsis. In the future, this knowledge can be used as a framework for understanding how all land plants respond to changes in their environment.
Plant and Cell Physiology, 2005
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Plant, Cell and Environment, 1997
Early attempts to identify the chromophore of the photoreceptor for phototropism are reviewed. Carotenoids and flavins were the principal candidates, but studies with grass coleoptiles devoid of carotenoids suggest that at least in these organs carotenoids are most unlikely to play that role. The status of characterization of a gene for a putative photoreceptor protein is also reviewed. As the action spectrum for phototropism resembles the absorption spectrum of a flavoprotein, flavoproteins are attractive candidates at present, especially since the CRYl photoreceptor in Arabidopsis thaliana that mediates blue light-dependent hypocotyl growth suppression has flavin adenine dinucleotide as one of its two chromophores. As the second chromophore appears to be pterin, pterins should not be ruled out as candidate chromophores for the photoreceptor for phototropism.
The Plant Journal, 1997
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The Phytochromes, a Family of Red/Far-red Absorbing Photoreceptors
Journal of Biological Chemistry, 2001
Because plants are photo-auxotrophic they are particularly sensitive to their light environment. To fine-tune their development according to light intensity, direction, spectral quality, and periodicity they possess a multiplicity of light sensors (1). In Arabidopsis there are eight identified photoreceptors, but this list is still incomplete. It includes three UV-A/blue light receptors (phototropin, a photoreceptor to sense light direction, and two cryptochromes that mediate many photomorphogenic responses (2, 3)) and five phytochromes (phy) 1 named phyA-phyE that absorb mainly red/far-red light, with phyA also responding to broad-spectrum light (UV-A to far-red) of very low intensity (4). All these photoreceptors bind to a chromophore, which for the phytochromes is a linear tetrapyrrole (phytochromobilin) (5). Because many light effects are induced by the co-action of several photoreceptors and because some photoreceptors regulate multiple aspects of photomorphogenesis, a genetic approach was instrumental for dissecting the specific roles of individual photoreceptors (1). As a consequence, research has concentrated on a few species that are particularly well suited for molecular genetic studies, in particular Arabidopsis (6). Multiple Phytochromes Have Overlapping and Distinct Functions Phytochromes were originally defined as the receptors responsible for red, far-red reversible, plant responses (7-9). Photobiological experiments led to the proposal that phy exists in two spectral forms: the inactive Pr form (red light absorbing) phototransforms into the active Pfr form (far-red light absorbing) upon absorption of red light. This reaction can be reversed when Pfr is converted to Pr upon absorption of far-red light. Purification of phy from plants confirmed the existence of those two spectrally interconvertible forms (10). phy are classified into two groups; type I (phyA in Arabidopsis) is light-labile and type II (phyB-phyE in Arabidopsis) is light-stable (11). Numerous recent reviews cover phy-mediated photomorphogenesis in detail (12-19). Photobiological and genetic studies have revealed that this small gene family plays important roles in seed germination, seedling de-etiolation, neighbor perception and avoidance, and the transition from vegetative to reproductive growth (induction of flowering). At the molecular and cellular level phy responses include: development of the chloroplast, inhibition or promotion of cell growth (depending on the organ), ion fluxes at the plasma membrane, and gene expression responses (1). Genetic screens to identify loci implicated in phy responses have yielded four apoprotein mutants (phyA, phyB, phyD, and phyE), two chromophore mutants (hy1 and hy2), and numerous mutants implicated in phy-mediated * This minireview will be reprinted in the 2001 Minireview Compendium, which will be available in December, 2001. This is the second article of three in the "Light Minireview Series.
Structure and Function of Plant Photoreceptors
Annual Review of Plant Biology, 2010
Signaling photoreceptors use the information contained in the absorption of a photon to modulate biological activity in plants and a wide range of organisms. The fundamental—and as yet imperfectly answered—question is, how is this achieved at the molecular level? We adopt the perspective of biophysicists interested in light-dependent signal transduction in nature and the three-dimensional structures that underpin signaling. Six classes of photoreceptors are known: light-oxygen-voltage (LOV) sensors, xanthopsins, phytochromes, blue-light sensors using flavin adenine dinucleotide (BLUF), cryptochromes, and rhodopsins. All are water-soluble proteins except rhodopsins, which are integral membrane proteins; all are based on a modular architecture except cryptochromes and rhodopsins; and each displays a distinct, light-dependent chemical process based on the photochemistry of their nonprotein chromophore, such as isomerization about a double bond (xanthopsins, phytochromes, and rhodopsins...
Photochemistry and Photobiology, 2000
The plant receptor phytochrome A (phyA) mediates responses like hypocotyl growth inhibition and cotyledon unfolding that require continuous far-red (FR) light for maximum expression (high-irradiance responses, HIR), and responses like seed germination that can be induced by a single pulse of FR (very-low-fluence responses, VLFR). It is not known whether this duality results from either phyA interaction with different end-point processes or from the intrinsic properties of phyA activity. Etiolated seedlings of Arabidopsis thaliana were exposed to pulses of FR (3 min) separated by dark intervals of different duration. Hypocotyl-growth inhibition and cotyledon unfolding showed two phases. The first phase (VLFR) between 0.17 and 0.5 pulses•h Ϫ1 , a plateau between 0.5 and 2 pulses•h Ϫ1 and a second phase (HIR) at higher frequencies. Reciprocity between fluence rate and duration of FR was observed within phases, not between phases. The fluence rate for half the maximum effect was 0.1 and 3 mol•m Ϫ2 •s Ϫ1 for hourly pulses of FR (VLFR) and continuous FR (HIR), respectively. Overexpression of phytochrome B caused dominant negative suppression under continuous but not under hourly FR. We conclude that phyA is intrinsically able to initiate two discrete photoresponses even when a single end-point process is considered.