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16 recordsLinked to original sources
PubMed2026

DNA-binding activity of PIF7 links phytochrome B signaling to plant responses to vegetation proximity.

PHYTOCHROME INTERACTING FACTORs (PIFs) are transcription factors that act as central signaling hubs in light-regulated processes. All PIFs contain an active phytochrome B-binding motif and a DNA-binding basic helix-loop-helix domain. In the shade-avoider Arabidopsis thaliana, PIF7 is a major promoter of hypocotyl elongation in response to vegetation proximity, becoming active when released from phytochrome B via its active phytochrome B-binding motif. Here we show that PIF7 promotes seedling elongation in other species, including the shade-avoider tomato and the shade-tolerant Cardamine hirsuta, suggesting that PIF7 has retained some of its key functional domains across diverse plants. Through complementation analyses using PIF7 variants lacking either the active phytochrome B-binding or basic helix-loop-helix domain, we demonstrate that, unlike PIF3, PIF7 versions unable to bind phytochrome B remain active regardless of light conditions, whereas loss of DNA-binding capacity fully disrupts PIF7 function. Our results further suggest that phytochrome B interaction imposes a dual regulatory control over PIF7, modulating both its abundance and its phosphorylation state (ie its ability to bind and regulate target genes).

Phytochrome B↗
PubMed1992

Isolation and characterization of a cDNA-clone coding for potato type B phytochrome.

We have isolated and sequenced overlapping genomic and cDNA clones encoding the apoprotein of a potato phytochrome. Based on the deduced amino acid sequence, which shows 77% identity to the Arabidopsis phyB and 50% identity to the potato phyA open reading frame, we suggest that these clones encode phyB phytochrome. However, the size of the deduced open reading frame of 1133 amino acids is smaller than the size of the other two phyB open reading frames characterized so far in higher plants, which contain 1171 or 1187 amino acids. The intron/exon structure within the coding region is conserved in phyA and phyB genes of various species. Southern blot analysis indicates that potato phyB is a single-copy gene. PhyB mRNA levels do not differ among different organs or different light regimes. Transcription initiation starts from two different start points which are 63 bp apart.

Amino Acid Sequence↗
PubMed1992

Phytochrome evolution: a phylogenetic tree with the first complete sequence of phytochrome from a cryptogamic plant (Selaginella martensii spring).

We have sequenced cDNA and genomic clones coding for phytochrome of the fern Selaginella. On the amino acid level, this phytochrome shares sequence homologies with phytochromes of higher plants which range between 62 (phytochrome B of Arabidopsis) and 55 (56)% [phytochrome C of Arabidopsis (Avena)]. Introns in the Selaginella gene are short and occupy positions known from phytochrome sequences of higher plants. A rooted phylogenetic tree based on mutation distances puts Selaginella phytochrome closest to the hypothetical ancestor. A similar tree arises if the tree is constructed with partial sequences (about 200 amino acids) around the chromophore attachment site. An extension of this tree by sequences of other cryptogamic plants (Mougeotia, Ceratodon, Psilotum) shows all these sequences including those of the phytochromes B and C of Arabidopsis on a branch, well separated from the branch formed by phytochromes known to accumulate in etiolated plants. The rooted phytochrome phylogenetic tree, however, is difficult to reconcile with the fossil record.

Amino Acid Sequence↗
PubMed1992

The cucumber long hypocotyl mutant lacks a light-stable PHYB-like phytochrome.

A novel cDNA sequence homologous to a phytochrome B (phyB) gene that was isolated in a library from tobacco tissue has been used in an Escherichia coli expression system to raise anti-phytochrome B (anti-PHYB) polypeptide-specific monoclonal antibodies. The specificity of these antibodies has been tested by cross-reactivity against purified pea light-labile type 1 and light-stable type 2 phytochromes, with some antibodies reacting with the type 2 and none with the type 1 phytochromes. One such antibody, monoclonal mAT1, has been employed to analyze the phytochrome molecular species present in a photomorphogenic long hypocotyl (lh) mutant of cucumber. The results indicated that the mutant contains wild-type levels of the light-labile type 1 phytochrome polypeptide (PHYA), which has an apparent molecular mass of approximately 120 kD, but shows less than 1% (detection limit) of a light-stable polypeptide recognized by mAT1 in wild-type seedlings. This protein, not detectable in the lh mutant, has the properties of light-stable type 2 phytochrome, has an apparent molecular mass of 116 to 117 kD, and remains at constant levels under continuous low-fluence-rate red light. Therefore, we conclude that the lh mutant lacks at least one type 2 phytochrome-like polypeptide, most probably a phyB gene product. The correlation between the lack of this protein and the deficiency or absence of physiological responses to a light-stable phytochrome species in this mutant helps to identify the physiological roles played by the products of different subfamilies within the phytochrome gene family.

Antibodies, Monoclonal↗
PubMed2025

A PIF-regulated switch in cell axis growth drives cotyledon expansion through tissue-specific cell expansion and division.

Despite its crucial role during seedling deetiolation, cotyledon expansion has been largely overlooked, with hypocotyl elongation favored as the primary phenotypic readout in light signaling research. Here, we investigate how cotyledon expansion is regulated during seedling establishment and reveal that light-induced cotyledon expansion involves a rapid switch in growth direction - from longitudinal in darkness to transversal upon initial light exposure. Using PIFq- and phyA/phyB-deficient Arabidopsis mutants, we demonstrate that this switch is repressed by PIFs in the dark and promoted by phytochromes under red light. Notably, expansion is antagonistically regulated in the light by GUN1-mediated plastid retrograde signaling. Cotyledon expansion involves rapid epidermis cell expansion, transitioning from rectangular in darkness to characteristic lobed cells in light. Importantly, our findings show that mesophyll extension is driven not only by cell enlargement but also by palisade cell division, consistent with an enrichment of cell cycle-related genes that are antagonistically regulated by the PIF/phy system and retrograde signaling in the cotyledon. Finally, using mutant lines expressing PIF1 and phyB specifically in the epidermis, we establish that epidermal expansion can drive palisade cell growth, while mesophyll cell division is predominantly regulated by light at the tissue-specific level. This study provides a novel framework for investigating cotyledon expansion during seedling deetiolation, incorporating tissue-level regulation. We propose that cotyledons serve as an excellent model for studying morphogenesis and organ geometry, which in plants is governed by directional cell growth.

Cotyledon↗
PubMed1976

Phytochrome system of the yeast Candida guilliermondii and recovery from ultraviolet injury.

The effect of red (660 nm) and far-red (730 nm) light on the stability of the yeast Candida guilliermondii to lethal u.v. radiation has been studied. Reactivation and protection were exhibited for 30 min after treatment with red light and were abolished by far-red exposure applied within this time period. The temperature dependence of the reactivation effect was also studied. The data obtained showed that the properties of recovery and protection against u.v. exposure are associated with the phytochrome system of the yeast.

Candida↗
PubMed1992

Synthesis of a functional anti-phytochrome single-chain Fv protein in transgenic tobacco.

We have expressed a synthetic gene that encodes an antigen-binding single-chain FV protein (scFV) in transgenic tobacco plants. The scFV gene was created by polymerase chain reaction (PCR) amplification of the variable domain coding regions from a mouse monoclonal hybridoma cell line. The monoclonal cell line secretes an IgG1 antibody that binds to the plant regulatory photoreceptor protein, phytochrome. The cloned scFV gene was expressed initially in Escherichia coli and shown to produce a 28 kD, phytochrome-binding binding scFV protein. Transgenic tobacco plants expressing the scFV gene were also found to produce a functional scFV protein, and seeds from transgenic R1 progeny displayed aberrant phytochrome-dependent germination. The scFV from transgenic tobacco could be isolated, to near homogeneity, by a single phytochrome-Sepharose affinity chromatography step.

Amino Acid Sequence↗
PubMed1992

Structural domains of phytochrome deduced from homologies in amino acid sequences.

A method of semiempirical identification of structural domains is proposed. The procedure is based on the comparison of amino acid sequences in groups of homologous proteins. This approach was tested using 32 known protein sequences from different cytochrome b5, cytochrome c, lysozyme, hemoglobin, and myoglobin proteins. The method presented was able to identify all structural domains of these reference proteins. A consensus secondary structure provided information on structural content of these domains predicting correctly 21 of 23 (91%) of alpha-helices. We applied this method to six homologous phytochrome sequences from Avena, Arabadopsis, Cucurbita, Maize, Oryza, and Pisum. Some of the identified domains can be assigned to the known tertiary structure categories. For example, an alpha/beta domain is localized in the region known to stabilize the phytochrome chromophore in the red light absorbing form (Pr). One alpha-helical and one alpha/beta domains are localized in regions important for the chromophore stabilization in the far-red absorbing form (Pfr). From an analysis of noncovalent interaction patterns in another domain it is proposed that a phytochrome dimer contact involves two segments localized between residues 730 and 821 (using numbering of aligned sequences). Also, a possible antiparallel beta-sheet structure of this region has been suggested. According to this model, the long axis of the interacting structures is perpendicular to a twofold symmetry axis of the phytochrome dimer.

Amino Acid Sequence↗
PubMed1975

The structures of the phytochrome chromophore in both photoreversible forms.

Spectral measurements of phytochrome are performed after unfolding of the peptide chain. By comparison with bile pigments of known structure, structure 1a, containing a hydrogenated ring A, is deduced for the PR chromophore. Its spectral properties indicate that the chromophore of the physiologically active PFR form has lost the double bond of the bridge joining rings A and B.

Bile Pigments↗
PubMed1992

Fourier transform resonance Raman spectroscopy of phytochrome.

The Pr and Pfr forms of phytochrome in H2O and D2O have been studied by Fourier transform resonance Raman spectroscopy with near-infrared excitation (1064 nm). It is demonstrated that this technique is a powerful method for analyzing the chromophore structures of photosensitive pigments. The high spectral quality allows discussion of vibrational assignments based on an empirical approach using previously published data obtained from model compounds. The reduction in intensity of a high-frequency band assigned to the ring-C/D methine bridge vibration is an indication for the non-coplanarity of the ring D in Pfr. The high intensity of a C-H out-of-plane vibration also supports this hypothesis. In Pr, a broad peak at approximately 1100 cm-1 is assigned to an out-of-plane vibration of a strongly hydrogen-bonded pyrrole C=NH+ group. It is missing in Pfr, suggesting deprotonation of the corresponding ring during the transformation from Pr to Pfr.

Chemical Phenomena↗
PubMed1976

Photoregulation of biologically active macromolecules.

A broad view is given of photoregulated processes as they occur in algae, fungi, halophilic bacteria, higher plants, invertebrates, and higher animals. Emphasis is on the following: the organs, tissues, and organelles that participate; the nature of the photoreceptor pigments; the light-induced structural changes that occur in the photopigments; and the way in which the photochemical events are believed to be translated into the physiological response. An attempt is made to show that there exist common biochemical attributes in all systems. In particular, they depend upon the ability of a low-molecular-weight to regulate a biologically active macromolecule, which may or may not be incorporated into a membrane. This is a common type of biochemical regulation and is, for example, the basis of allosterism. The additional refinement in photosensitive systems is the ability of light to alter the stereochemistry of the low-molecular-weight effector molecule and thus to modify its effect on the macromolecule. Model photosensitive systems are examined that incorporate control mechanisms that function in natural systems. For example, there are systems in which enzymes, normally insensitive to light, are made subject to photoregulation. In others, membrane permeability is rendered photoresponsive. A comparison of the model systems was processes found in nature permits the formulation of an hypothesis to explain how naturally occurring photoresponsive systems might have evolved.

Bacteria↗
PubMedDate not supplied

[Role of phycobilin pigments in photosynthesis].

Experimental data on possible role of phicobilliprotein (PhBP) in photosynthesis are analysed. It is concluded that the widely spread notion about PhBP only as the light-gathering pigments which transfer the energy to chlorophyll, turned to be insufficiently substantiated experimentally until recently. At the same time the discovered ability of PhBP for reversible redox transformations together with the new data on the nature of fluorescence of blue-green algae and PhBP localization in the cell allowed a suggestion that PhBP can independently of chlorophyll or together with it directly participate in photochemical reactions of photosynthesis. A suggestion is advanced concerning possible existence of the reaction centres of PhBP in phicobillisomes.

Hydrogen-Ion Concentration↗
PubMed1992

Nucleotide sequence of a tobacco cDNA encoding plastidic glutamine synthetase and light inducibility, organ specificity and diurnal rhythmicity in the expression of the corresponding genes of tobacco and tomato.

A full-length cDNA encoding glutamine synthetase (GS) was cloned from a lambda gt10 library of tobacco leaf RNA, and the nucleotide sequence was determined. An open reading frame accounting for a primary translation product consisting of 432 amino acids has been localized on the cDNA. The calculated molecular mass of the encoded protein is 47.2 kDa. The predicted amino acid sequence of this precursor shows higher homology to GS-2 protein sequences from other species than to a leaf GS-1 polypeptide sequence, indicating that the cDNA isolated encodes the chloroplastic isoform (GS-2) of tobacco GS. The presence of C- and N-terminal extensions which are characteristic of GS-2 proteins supports this conclusion. Genomic Southern blot analysis indicated that GS-2 is encoded by a single gene in the diploid genomes of both tomato and Nicotiana sylvestris, while two GS-2 genes are very likely present in the amphidiploid tobacco genome. Western blot analysis indicated that in etiolated and in green tomato cotyledons GS-2 subunits are represented by polypeptides of similar size, while in green tomato leaves an additional GS-2 polypeptide of higher apparent molecular weight is detectable. In contrast, tobacco GS-2 is composed of subunits of identical size in all organs examined. GS-2 transcripts and GS-2 proteins could be detected at high levels in the leaves of both tobacco or tomato. Lower amounts of GS-2 mRNA were detected in stems, corolla, and roots of tomato, but not in non-green organs of tobacco. The GS-2 transcript abundance exhibited a diurnal fluctuation in tomato leaves but not in tobacco leaves. White or red light stimulated the accumulation of GS-2 transcripts and GS-2 protein in etiolated tomato cotyledons. Far-red light cancelled this stimulation. The red light response of the GS-2 gene was reduced in etiolated seedlings of the phytochrome-deficient aurea mutant of tomato. These results indicate a phytochrome-mediated light stimulation of GS-2 gene expression during greening in tomato.

Amino Acid Sequence↗
PubMed1977

Studies on plant bile pigments, II[1]. Chemical and photochemical oxygenation of a phytochrome Pr chromophore model pigment to purpurins.

The chemical and photochemical oxygenation of 2,3-dihydrooctaethyl-1,19(21,24H)-bilindione (1), as a model for the chromophores of both phytochrome Pr and phycocyanin, has been studied in neutral and alkaline solution, and in the presence of zinc ions. By comparison with octaethyl-1,19(21,24H)-bilindione (5), the influence of ring A hydrogenation on the reactivity of bilins has been assessed. In the dark, 1 is attacked selectively and rapidly at C-5 yielding "purpurins", while 5 reacts slowly, and is attacked predominantly at C-10. Photooxidation of 5 yields the tripyrrinic "purpurin" 7 only. Photoreactivity of 1 is considerably enhanced, yielding "purpurins" and "violins" rapidly. In spite of UV-vis and mass spectroscopic similarities, the "purpurin" 7 differs from the "purpurins" 6a,b by the loss of ring A. The facile cleavage at the C-5 methine bridge and the spectroscopic properties of "purpurins" are discussed.

Models, Chemical↗
PubMed1992

Production and secretion of a bifunctional staphylococcal protein A::antiphytochrome single-chain Fv fusion protein in Escherichia coli.

A bifunctional molecule was genetically engineered which contained the secretory signal and four Fc-binding domains of Staphylococcus aureus protein A (FcA), fused to a single-chain Fv (scFv) derived from an immunoglobulin (Ig) G1 mouse monoclonal antibody (AS32) directed against the plant regulatory photoreceptor protein, phytochrome. The FcA::AS32scFv sequence was encoded in a single synthetic gene and expressed as a 60-kDa periplasmic protein in Escherichia coli. The bifunctionality of the fusion protein was established by its ability to bind to both IgG-agarose and phytochrome-sepharose. Growth of cultures, producing the FcA::AS32scFv, at 37 degrees C, resulted in a decrease in the periplasmic accumulation of the fusion protein, and an increased accumulation of an assumed degradation product which retained Fc-binding activity. Growth of cultures at lower temperatures favoured the accumulation of undegraded fusion protein. The recombinant fusion protein could be purified to homogeneity by a simple, rapid chromatography procedure.

Animals↗