Eukaryotic algal phytochromes span the visible spectrum (original) (raw)
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An Evolutionarily Conserved Signaling Mechanism Mediates Far-Red Light Responses in Land Plants
The Plant Cell, 2013
Phytochromes are plant photoreceptors important for development and adaptation to the environment. Phytochrome A (PHYA) is essential for the far-red (FR) high-irradiance responses (HIRs), which are of particular ecological relevance as they enable plants to establish under shade conditions. PHYA and HIRs have been considered unique to seed plants because the divergence of seed plants and cryptogams (e.g., ferns and mosses) preceded the evolution of PHYA. Seed plant phytochromes translocate into the nucleus and regulate gene expression. By contrast, there has been little evidence of a nuclear localization and function of cryptogam phytochromes. Here, we identified responses to FR light in cryptogams, which are highly reminiscent of PHYA signaling in seed plants. In the moss Physcomitrella patens and the fern Adiantum capillus-veneris, phytochromes accumulate in the nucleus in response to light. Although P. patens phytochromes evolved independently of PHYA, we have found that one clad...
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.
A Brief History of Phytochromes
ChemPhysChem, 2010
Photosensory proteins enable living things to detect the quantity and quality of their light environment and to transduce that physical signal into biochemical outputs which entrain their metabolism with the ambient light environment. Phytochromes, which photoconvert between red-absorbing Pr and far-red-absorbing Pfr states, have been the most extensively studied of these interesting proteins. Critical regulators of a number of key adaptive processes in higher plants, including photomorphogenesis and shade avoidance, phytochromes are widespread in photosynthetic and nonphotosynthetic bacteria and even in fungi. Cyanobacterial genomes also possess a plethora of more distant relatives of phytochromes known as cyanobacteriochromes (CBCRs). Biochemical characterization of representative CBCRs has demonstrated that this class of photosensors exhibit a broad range of wavelength sensitivities, spanning the entire visible spectrum. Distinct protein-bilin interactions are responsible for this astonishing array of wavelength sensitivities. Despite this spectral diversity, all members of the extended family of phytochrome photosensors appear to share a common photochemical mechanism for light sensing: photoisomerization of the 15/16 double bond of the bilin chromophore.
Current biology : CB, 2016
Plants in dense vegetation perceive their neighbors primarily through changes in light quality. Initially, the ratio between red (R) and far-red (FR) light decreases due to reflection of FR by plant tissue well before shading occurs. Perception of low R:FR by the phytochrome photoreceptors induces the shade avoidance response [1], of which accelerated elongation growth of leaf-bearing organs is an important feature. Low R:FR-induced phytochrome inactivation leads to the accumulation and activation of the transcription factors PHYTOCHROME-INTERACTING FACTORs (PIFs) 4, 5, and 7 and subsequent expression of their growth-mediating targets [2, 3]. When true shading occurs, transmitted light is especially depleted in red and blue (B) wavelengths, due to absorption by chlorophyll [4]. Although the reduction of blue wavelengths alone does not occur in nature, long-term exposure to low B light induces a shade avoidance-like response that is dependent on the cryptochrome photoreceptors and th...
Phytochrome diversity in green plants and the origin of canonical plant phytochromes
Nature communications, 2015
Phytochromes are red/far-red photoreceptors that play essential roles in diverse plant morphogenetic and physiological responses to light. Despite their functional significance, phytochrome diversity and evolution across photosynthetic eukaryotes remain poorly understood. Using newly available transcriptomic and genomic data we show that canonical plant phytochromes originated in a common ancestor of streptophytes (charophyte algae and land plants). Phytochromes in charophyte algae are structurally diverse, including canonical and non-canonical forms, whereas in land plants, phytochrome structure is highly conserved. Liverworts, hornworts and Selaginella apparently possess a single phytochrome, whereas independent gene duplications occurred within mosses, lycopods, ferns and seed plants, leading to diverse phytochrome families in these clades. Surprisingly, the phytochrome portions of algal and land plant neochromes, a chimera of phytochrome and phototropin, appear to share a common...
Light signaling in photosynthetic eukaryotes with ‘green’ and ‘red’ chloroplasts
Environmental and Experimental Botany, 2015
Light drives one of the most important processes on earthphotosynthesis. Besides providing the energy for carbon reduction, it is also an important signaling source, which largely influences the acclimation and adaptation behavior of algae and plants. Two different ways of light perception can be differentiated: direct and indirect light signaling. Direct light signaling is based on the action of photoreceptors. Indirect light signaling originates from the photosynthetic light reaction and is either based on the redox state of the photosynthetic electron transport chain or on reactive oxygen species. Especially the indirect signaling raises a specific challenge for plants and algae: while the signal perception occurs in the chloroplast, the largest part of the target genes is located in the nucleus, i.e. the triggering signal needs to cross several membranes. Green algae and plants (the "greens") achieved to establish mechanisms which transfer the so called "retrograde" signal from the chloroplast into the nucleus. Besides identifying the primary light triggers and regulated target genes, researchers discovered a bunch of secondary messengers, which may connect the light trigger with the target genes in a signaling network. Still, the exact signaling cascades are basically unknown so far.
Phytochrome-mediated light signaling in plants: emerging trends
Physiology and Molecular Biology of Plants, 2008
Like other living organisms, plant development is also determined genetically but is modulated dramatically by diverse environmental signals. Among these, light plays a profound role and regulates virtually all aspects of plant life cycle, starting from seed germination through to senescence. Plants perceive changes in the ambient light environment by distinct sensory photoreceptors. The conventional photoreceptors include three major classes in plants, viz. the red/far-red (R/FR) light-sensing phytochromes and UV-A/blue light-perceiving cryptochromes and phototropins (Jiao et al., 2007). However, the molecular nature of the UV-B (280-320 nm) photoreceptor(s) is still elusive. Recently, additional blue light photoreceptors called ZEITLUPE have been characterized (