The plant photoreceptor phytochrome is organised in a small gene family with phytochrome a phya being unique, because it is specifically degraded upon activation by light. In contrast, all streptophytes examined so far have phytochromes that lack a his residue critical for phosphorelay. Probing the photoreaction mechanism of phytochrome through. Structure of the y263f mutant of the cyanobacterial phytochrome cph1. Each subunit consists of two components light absorbing pigment molecule, chromophore and a. Phytochrome mediated photomorphogenic responses are characterized by the complex variety of relationships between light input and physiological outputs, including. Carvalho rf, campos ml, azevedo ra 2011 the role of phytochrome in stress tolerance. Light perception and signalling by phytochrome a journal. Lysine 206 in arabidopsis phytochrome a is the major site. Phytochromes in prasinophytes contain an intact histidine kinase domain with lightdependent kinase activity, which could mediate phytochrome signaling duanmu et al. The photosensory region of plant phytochromes is therefore very likely to adopt a fold similar to that of dr bphp. Therefore, phytochrome induced phosphorylation and proteolysis of pifs may represent a major biochemical mechanism of signal transfer from the photoactivated phytochromes to their interacting signaling partners in the nucleus, which rapidly.
Phya is expressed at high levels in the cytoplasm in the inactive pr form in the dark. Phytochrome threedimensional structures and functions. Akira nagatanis group reported 15 years ago that arabidopsis phyb contains putative nuclear localization signals nlss and could be localized to the nucleus. The present work contributed to the understanding of the subfunctionalization of phytochrome signaling in an evolutionary context. Phytochrome c phyc is a lowabundance member of the fivemembered phytochrome family of photoreceptors in arabidopsis. Domain arrangements in plant, bacterial and fungal phytochromes are comparable insofar, as the three nterminal domains are always pas, gaf and phy domains. Role of the phytochrome and cryptochrome signaling.
Perarntsim pas domains serve as versatile sensor and interaction modules in signal transduction proteins. Although its overall architecture and chromophoreprotein contacts are reminiscent. Although the crystal structures of dark and lightadapted states have been determined, the molecular mechanisms underlying photoactivation remain elusive. Much of plant growth and development is regulated by the phytochrome phy family of photoreceptors. Subsequent studies using phytochromes fused with a fluorescent protein tag confirmed these earlier results and further demonstrated that the. Crystal structure of the photosensing module from a red. There are five distinct phytochromes in arabidopsis thaliana, designated phytochrome a phya to phye. Molecular mechanisms of prokaryotic phytochrome signaling. Phytochrome structure and signaling mechanisms, annual. A photoresponse can be defined as phytochrome mediated one if it could be induced by a short irradiation of red light nearly 5 min or so, of medium quantum flux density. Phytochrome nuclear accumulation is the earliest detectable light response. The determination of the drbphp crystal structure will permit much more detailed elucidation of the phytochrome photocycle as well as development of the next generation of structural hypotheses about phytochrome signaling in many organisms. The upper panels show a typical image of rpt2 signals.
Biointerfaces 45 2005 154161 molecular mechanisms of phytochrome signal transduction in higher plants liye chua,b,1, hongbo shaoa,b,c. Interestingly, distinct phospho signaling pathways that are triggered by phot1 and phot2 are used for phototropism, chloroplast movement and stomatal opening, respectively. Phytochromes and phytochrome interacting factors plant. Phytochrome structure and signaling mechanisms phytochrome structure and signaling mechanisms rockwell, nathan c su, yishin. The phytochrome redfarred photoreceptor superfamily. The function of phytochrome as redfarred light sensors has been investigated extensively in terms of photochemistry, protein structures, and. In view of the close evolutionary relationship of prasinophytes and streptophytes fig.
The protein part comprises two identical chains a and b. Haiyang wang and xing wang deng, phytochrome signaling mechanisms, the arabidopsis book, 10. Phytochrome is a soluble chromoprotein with a molecular mass of 250 kda it occurs as a dimer made up of two subunits, each of 125 kda. Structure and signaling mechanism of perarntsim domains. Request pdf phytochome structure and signaling mechanisms phytochromes are a widespread family of redfarred responsive photoreceptors first discovered in plants, where they constitute one of. Phytochrome a requires jasmonate for photodestruction. Here, we demonstrate that the conserved tongue region of the phy domain of a 57kda photosensory module of deinococcus radiodurans phytochrome changes from a structurally heterogeneous dark. The earliest phytochrome signaling events after excitation by red light include their rapid translocation from the cytoplasm to subnuclear bodies photobodies that contain other proteins involved in photomorphogenesis, including a number of transcription factors and e3 ligases. Light initiates chloroplast biogenesis by controlling gene expression in plastids. It identifies functions to be performed by a signaling system network and a protocol to enable their performance.
However, precise mechanism of its action has been described in an oversimplified way and many questions about the mechanism of its action await detailed answers. Over the past few years the first threedimensional structures of phytochrome lightsensing domains from bacteria have been determined. Photomorphogenesis is the process by which plants grow and develop in response to light signals. The only lightlabile phytochrome phya mainly mediates photomorphogenic reactions in fr light li et al. Marine algae and land plants share conserved phytochrome. Molecular mechanisms of phytochrome signal transduction in. This process is mediated by a sophisticated network of photoreceptors among which phytochromes play a key role. This structure reveals several key surprises that could not have been reliably predicted, including the chromophore configuration and the trefoil knot. Diverse photoreceptors and light responses in plants. Rather, phya nuclear localization requires binding to a pair of plantspecific proteins, fhy1 and its paralog fhl fhy1like, both of which contain a conserved nls and shuttle phya to the nucleus 39, 40, 41. Phytochromes consist of a protein, covalently linked to a lightsensing bilin chromophore.
Phytochrome a is the only phytochrome that translocates to the nucleus under farred light conditions 23. Therefore, phytochrome induced phosphorylation and proteolysis of pifs may represent a major biochemical mechanism of signal transfer from the photoactivated phytochromes to their interacting signaling partners in the nucleus, which rapidly alters the gene expression profiles of the genome. Phytochrome activates the plastidencoded rna polymerase. Phya induces flowering, and regulates seed germination, seedling photomorphogenesis, and accumulation. As they emerge from the ground, seedlings adopt a photosynthetic lifestyle, which is accompanied by dramatic changes in morphology and global alterations in gene expression that optimizes the plant body plan for light capture. Although signalling theory was initially developed by michael spence based on observed knowledge gaps between organisations and prospective employees, its intuitive nature led it to be adapted to. Molecular mechanisms underlying phytochromecontrolled. Introduction light is a major environmental signal influencing a multitude of steps in plant development such as seed germination, carbon assimilation, stem elongation, leaf morphology, flowering and many others. In contrast to this chemical, physical, and functional diversity, the structure of the core of pas domains is broadly conserved and comprises a fivestranded. Experimental data indicate that phyc may have some physiological roles that are different to those of phya and phyb. Phytochromes are red rfarred fr light photoreceptors that play fundamental roles in photoperception of the light environment and the subsequent adaptation of plant growth and development. Phytochrome signaling mechanisms and the control of plant. Proteins of the phytochrome superfamily of redfarred light receptors have a variety of biological roles in plants, algae, bacteria and fungi and demonstrate a diversity of spectral sensitivities and output signaling mechanisms. Structural photoactivation of a fulllength bacterial.
Phytochome structure and signaling mechanisms request pdf. These spatiotemporal phytochrome responses are central to coordinated plant growth, development and metabolism, yet we are truly at the forefront of understanding the structure and coordination of the signaling networks downstream of the photoreceptors that impact distinct lightdependent growth responses. In addition, regions most conserved in the extended phytochrome family map to the dr bphp pas and gaf cores, with sequence variability, gaps, and insertions falling within surface loops figure 2a. Signal transfer by prokaryotic phytochromes most frequently utilizes the two component signaling paradigm, i. The regulatory mechanism for phya nuclear accumulation is more complex. The mechanism by which photoactivated phytochrome transfers its signalling information to its signalling partners in plant cells has been of. The signaling mechanisms from light perception to cellular responses have recently been revealed in detail in phototropinmediated responses. Pas sensors detect chemical and physical stimuli and regulate the activity of functionally diverse effector domains. A major phytochrome regulating deetiolation reaction in r light, phyb also mediates rfr reversible responses and is one of the four lightstable phytochromes li et al. Chromophore structure in the photocycle of the cyanobacterial phytochrome cph1. Phytochromes are a widespread family of redfarred responsive photoreceptors first discovered in plants, where they constitute one of the three main classes of photomorphogenesis regulators. We present an atomic perspective of plant phy signaling through a crystal structure of the photosensing module as pr from arabidopsis phyb assembled with its native chromophore phytochromobilin. Phytochrome measures the ratio of red light r to farred. Although threedimensional structures of both states have been reported, the photoconversion and intramolecular signaling mechanisms are still unclear.
Ppks mediate direct signal transfer from phytochrome. Phytochrome signal transduction pathways are regulated by. In etiolated seedlings, phytochrome a phya mediates verylowfluence responses vlfrs, which initiate deetiolation at the interphase between the soil and aboveground environments, and highirradiance responses hir, which complete deetiolation under dense canopies and require more sustained activation with farred light. Phytochromes are present in all land plants and most green algal lineages, except in the chlorophytes li et al. All higher plants possess multiple phytochrome photoreceptors, with phytochrome a phya being light labile and other members of the family being relatively light stable phybphye in arabidopsis arabidopsis thaliana. Fhy1 and fhl are required for both phya nuclear accumulation and its.
This so called photodestruction is thought to be important for dynamic aspects of sensing such as measuring day length or shading by competitors. However, the signaling mechanisms might be different. Figure 1 provides a representative illustration of the domain sequence and structure of bacterial phytochromes. Phytochrome signaling mechanisms jigang lia,b, gang li b, haiyang wang, and xing wang denga,b,1 a pekingyale joint center for plant molecular genetics and agrobiotechnology, state key laboratory of protein and plant gene research, college of life sciences, peking university, beijing 100871, china. Involvement of phya and cryptochromes in rpt2 expression and hypocotyl phototropism. Signaltriggered proteolytic degradation has emerged as central. Each chain has a pas domain, gaf domain and phy domain. Signaling system 7 ss7 is an architecture for performing outofband signaling in support of the callestablishment, billing, routing, and informationexchange functions of the public switched telephone network pstn. The role of phytochrome in stress tolerance wiley online. Phytochrome threedimensional structures prokaryotic phytochromes provided not only the missing link between plant phytochromes and their shpk ancestors and thereby a clear domain map for the phytochrome family, but also access to powerful biophysical methods such as xray crystallography and nmr on account of the relative ease with. Phytochrome structure and signaling mechanisms annual. The discovery of bacterial homologs led to the determination of a series of threedimensional structures of phytochrome fragments 916. Phytochrome a protein is known to be degraded rapidly in response to light absorption after conformational change into the pfr form. Frontiers spatiotemporal phytochrome signaling during.
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