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At least 19 recordsLinked to original sources
PubMed1989

Calcium requirement of phytochrome-mediated fern-spore germination: no direct phytochrome-calcium interaction in the phytochrome-initiated transduction chain.

Phytochrome-mediated germination of fern spores of Dryopteris paleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h of imbibition. For its realization external Ca2+ was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10(-4) M. At concentrations > or = 10(-1) M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La3+, an antagonist of Ca2+. From these results it is concluded that Ca2+ influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca2+ the R-stimulated system remained capable of responding to Ca2+, added as late as 40 h after R. Moreover, Ca2+ was effective even if added after the active form of phytochrome, Pfr, had been abolished by far-red (FR) 24 h after R. Thus, the primary effect of Pfr, that initiates the transduction chain, does not require calcium. "Coupling" of Pfr to subsequent dark reactions has been investigated by R-FR irradiations with various dark intervals. The resulting "escape kinetics" were characterized by a lag phase (6 h) and half-maximal escape from FR reversibility (19 h). These kinetics were not significantly changed by the presence or absence of calcium. Thus, direct interaction of Pfr and calcium is not a step in the transduction chain initiated by the active form of phytochrome.

Calcium↗
PubMed1989

Ubiquitin-phytochrome conjugates. Pool dynamics during in vivo phytochrome degradation.

The plant photoreceptor chromoprotein, phytochrome, is rapidly degraded in vivo after photoconversion from a stable red light-absorbing form (Pr) to a far-red light-absorbing form (Pfr). Previously, we demonstrated that during Pfr degradation in etiolated oat seedlings, ubiquitin-phytochrome conjugates, (Ub-P), appear and disappear suggesting that phytochrome is degraded via a ubiquitin-dependent proteolytic pathway (Shanklin, J., Jabben, M., and Vierstra, R. D. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 359-363). Here, we provide additional kinetic and localization data consistent with this hypothesis by exploiting the unique ability to photoregulate phytochrome degradation in vivo. An assay for the quantitation of Ub-P was developed involving immunoprecipitation of total conjugates with anti-ubiquitin antibodies, followed by the detection of Ub-P with anti-phytochrome antibodies. Using this immunoassay, we found that Ub-P will accumulate to approximately 5% of initial phytochrome during Pfr degradation induced by a saturating red light pulse. Reducing the amount of Pfr produced initially by attenuating the red light pulse, lowered the amount of phytochrome degraded in the following dark period and concomitantly reduced the maximal accumulation of Ub-P. Continuous far-red irradiations that maintained only 4% of phytochrome as Pfr induced rapid phytochrome degradation similar to that induced by a red light pulse converting 86% of Pr to Pfr. The appearance and disappearance of Ub-P were similar for each irradiation indicating that Ub-P accumulation is independent of the level of Pfr provided rapid phytochrome degradation is maintained. Pulse-chase studies employing continuous far-red light followed by darkness showed that Ub-P are continuously synthesized during phytochrome degradation and rapidly disappear once degradation ceases. Ub-P also accumulated during "cycled Pr" degradation induced by the transformation of Pr to Pfr and back to Pr. The commitment to degrade cycled Pr and form Ub-P occurred within seconds after Pfr formation making the cause(s) underlying this phenomenon one of the fastest phytochrome reactions known. Within seconds after Pfr formation, a majority of phytochrome is also known to aggregate in vivo (previously defined as sequestered or pelletable), with aggregated phytochrome preferentially lost during phytochrome degradation. In vitro analysis of aggregated phytochrome indicated that they contain most of the Ub-P. Moreover, the appearance of Ub-P in the aggregated and soluble fractions correlated with the time that phytochrome disappeared from that fraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Edible Grain↗
PubMed1999

Overexpression of rice phytochrome A partially complements phytochrome B deficiency in Arabidopsis.

The red/far-red reversible phytochromes play a central role in regulating the development of plants in relation to their light environment. Studies on the roles of different members of the phytochrome family have mainly focused on light-labile, phytochrome A and light-stable, phytochrome B. Although these two phytochromes often regulate identical responses, they appear to have discrete photosensory functions. Thus, phytochrome A predominantly mediates responses to prolonged far-red light, as well as acting in a non-red/far-red-reversible manner in controlling responses to light pulses. In contrast, phytochrome B mediates responses to prolonged red light and acts photoreversibly under light-pulse conditions. However, it has been reported that rice (Oryza sativa L.) phytochrome A operates in a classical red/far-red reversible fashion following its expression in transgenic tobacco plants. Thus, it was of interest to determine whether transgenic rice phytochrome A could substitute for loss of phytochrome B in phyB mutants of Arabidopsis thaliana (L.) Heynh. We have observed that ectopic expression of rice phytochrome A can correct the reduced sensitivity of phyB hypocotyls to red light and restore their response to end-of-day far-red treatments. The latter is widely regarded as a hallmark of phytochrome B action. However, although transgenic rice phytochrome A can correct other aspects of elongation growth in the phyB mutant it does not restore other responses to end-of-day far-red treatments nor does it restore responses to low red:far-red ratio. Furthermore, transgenic rice phytochrome A does not correct the early-flowering phenotype of phyB seedlings.

Arabidopsis↗
PubMed1982

Comparative Phytochrome Immunochemistry as Assayed by Antisera against Both Monocotyledonous and Dicotyledonous Phytochrome.

Preparation and characterization of antisera against lettuce (Lactuca sativa L., cv. Grand Rapids) and pea (Pisum sativum L., cv. Alaska) phytochrome is described. These antisera, together with previously obtained antisera against zucchini (Cucurbita pepo L., cv. Black Beauty) and oat (Avena sativa L., cv. Garry) phytochrome, were used to compare by Ouchterlony double immunodiffusion phytochrome isolated from etiolated lettuce, pea, bean (Phaseolus vulgaris L., cv. Taylor Horticultural Bush), zucchini, oat and rye (Secale cereale L., cv. Balbo) seedlings. Cross reactivity between monocotyledonous phytochrome and antidicotyledonous-phytochrome serum and between dicotyledonous phytochrome and antimonocotyledonous-phytochrome serum was always weak or not perceptible by this assay. Among the four dicotyledonous phytochromes examined, pea and bean were the most similar immunochemically as anticipated. Pea and lettuce phytochrome somewhat unexpectedly also exhibited similar immunochemical reactivity. Zucchini phytochrome by contrast was immunochemically distinct from pea, bean, and lettuce phytochrome, although it did react with all three antidicotyledonous-phytochrome sera. Initial attempts to identify immunoglobulins that would recognize phytochrome regardless of its source indicated that they may exist. Such immunoglobulins are of interest because they might react with one or more determinants that could be part of an active site of phytochrome. These immunoglobulins, once isolated, could thus serve as a potential probe for the active site of phytochrome.

Journal Article↗
PubMed1995

An amino-terminal deletion of rice phytochrome A results in a dominant negative suppression of tobacco phytochrome A activity in transgenic tobacco seedlings.

Overexpression of phytochrome A results in an increased inhibition of hypocotyl elongation under red and far-red light. We used this approach to assay for the function of N-terminal mutations of rice (Oryza sativa L.) phytochrome A. Transgenic tobacco seedlings that express the wild-type rice phytochrome A (RW), a rice phytochrome A lacking the first 80 amino acids (NTD) or a rice phytochrome A with a conversion of the first 10 serines into alanine residues (S/A) were compared with untransformed wild-type tobacco (Nicotiana tabacum L. cv. Xanthi) seedlings. Experiments under different fluence rates showed that RW and, even more strongly, S/A increased the response under both red and far-red light, whereas NTD decreased the response under far-red light but hardly altered the response under red light. These results indicate that NTD not only lacks residues essential for an increased response under red light but also distorts the wild-type response under far-red light. Wild-type rice phytochrome A and, even more so, S/A mediate an enhanced phytochrome A as well as phytochrome B function, whereas NTD interferes with the function of endogenous tobacco phytochrome A as well as that of rice phytochrome A when co-expressed in a single host. Experiments with seedlings of different ages and various times of irradiation under far-red light demonstrated that the effect of NTD is dependent on the stage of development. Our results suggest that the lack of the first 80 amino acids still allows a rice phytochrome A to interact with the phytochrome transduction pathway, albeit non-productively in tobacco seedlings.

Base Sequence↗
PubMed1997

Computer analysis of phytochrome sequences and reevaluation of the phytochrome secondary structure by Fourier transform infrared spectroscopy.

A repertoire of various methods of computer sequence analysis was applied to phytochromes in order to gain new insights into their structure and function. A statistical analysis of 23 complete phytochrome sequences revealed regions of non-random amino acid composition, which are supposed to be of particular structural or functional importance. All phytochromes other than phyD and phyE from Arabidopsis have at least one such region at the N-terminus between residues 2 and 35. A sequence similarity search of current databases indicated striking homologies between all phytochromes and a hypothetical 84.2-kDa protein from the cyanobacterium Synechocystis. Furthermore, scanning the phytochrome sequences for the occurrence of patterns defined in the PROSITE database detected the signature of the WD repeats of the beta-transducin family within the functionally important 623-779 region (sequence numbering of phyA from Avena) in a number of phytochromes. A multiple sequence alignment performed with 23 complete phytochrome sequences is made available via the IMB Jena World-Wide Web server (http://www.imb-jena.de/PHYTO.html). It can be used as a working tool for future theoretical and experimental studies. Based on the multiple alignment striking sequence differences between phytochromes A and B were detected directly at the N-terminal end, where all phytochromes B have an additional stretch of 15-42 amino acids. There is also a variety of positions with totally conserved but different amino acids in phytochromes A and B. Most of these changes are found in the sequence segment 150-200. It is, therefore, suggested that this region might be of importance in determining the photosensory specificity of the two phytochromes. The secondary structure prediction based on the multiple alignment resulted in a small but significant beta-sheet content. This finding is confirmed by a reevaluation of the secondary structure using FTIR spectroscopy.

Amino Acid Sequence↗
PubMed1994

Pr-specific phytochrome phosphorylation in vitro by a protein kinase present in anti-phytochrome maize immunoprecipitates.

Protein kinase activity has repeatedly been found to co-purify with the plant photoreceptor phytochrome, suggesting that light signals received by phytochrome may be transduced or modulated through protein phosphorylation. In this study immunoprecipitation techniques were used to characterize protein kinase activity associated with phytochrome from maize (Zea mays L.). A protein kinase that specifically phosphorylated phytochrome was present in washed anti-phytochrome immunoprecipitates of etiolated coleoptile proteins. No other substrate tested was phosphorylated by this kinase. Adding salts or detergents to disrupt low-affinity protein interactions reduced background phosphorylation in immunoprecipitates without affecting phytochrome phosphorylation, indicating that the protein kinase catalytic activity is either intrinsic to the phytochrome molecule or associated with it by high-affinity interactions. Red irradiation (of coleoptiles or extracts) sufficient to approach photoconversion saturation reduced phosphorylation of immunoprecipitated phytochrome. Subsequent far-red irradiation reversed the red-light effect. Phytochrome phosphorylation was stimulated about 10-fold by a co-immunoprecipitated factor. The stimulatory factor was highest in immunoprecipitates when Mg2+ was present in immunoprecipitation reactions but remained in the supernatant in the absence of Mg2+. These observations provide strong support for the hypothesis that phytochrome-associated protein kinase modulates light responses in vivo. Since only phytochrome was found to be phosphorylated, the co-immunoprecipitated protein kinase may function to regulate receptor activity.

Antibodies↗
PubMed1975

Phytochrome Characterization by Rabbit Antiserum against High Molecular Weight Phytochrome.

Both small and large sizes of phytochrome purified from Garry oat (Avena sativa L. ev. Garry) as well as large phytochrome purified from Newton oat (A. sativa L. cv. Newton), rye (Secale cereale L. cv. Balbo), barley (Hordeum vulgare L. cv. Harrison), and pea (Pisum sativum L. cv. Alaska) seedlings are characterized by a specific antiserum against large Garry oat phytochrome. A spur is observed by double diffusion assay against large and small Garry oat phytochrome indicating only partial identity. In micro-complement fixation assays, large Garry oat phytochrome yields greater activity than small Garry oat phytochrome. In addition, the peak of activity is shifted to a higher antigen concentration with small phytochrome. Phytochrome, red-absorbing form, and phytochrome, far redabsorbing form, are indistinguishable by both double diffusion and micro-complement fixation assay. The different grass phytochromes are antigenically identical by double diffusion assay. Immunoelectrophoretic analyses of oat and rye large phytochrome, after proteolysis, suggest that there are one or a few regions of the molecule especially susceptible to hydrolysis by a wide variety of endopeptidases.

Journal Article↗
PubMed1993

Mosses do express conventional, distantly B-type-related phytochromes. Phytochrome of Physcomitrella patens (Hedw.).

We have screened a cDNA library of the moss Physcomitrella patens (Hedw.) for phytochrome sequences. The isolated sequences turned out to encode a phytochrome dissimilar to the phytochrome type postulated for the moss Ceratodon [(1992) Plant Mol. Biol. 20, 1003-1017] Physcomitrella phytochrome was completely alignable to fern phytochrome (Selaginella) and phytochromes of higher plants. The frequency of clones encoding this phytochrome indicated that a Ceratodon-like type should only be expressed, if at all, with lower frequencies than the sequenced phytochrome cDNA. Sequence differences between lower plant phytochromes are small as compared to phytochrome types of higher plants.

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↗
PubMed1985

Structure function studies on phytochrome. Identification of light-induced conformational changes in 124-kDa Avena phytochrome in vitro.

Light-mediated conformational changes in highly purified 124-kDa phytochrome preparations from etiolated oat seedlings have been identified by steric exclusion high performance liquid chromatography and limited proteolytic studies. Steric exclusion high performance liquid chromatography studies of oat and rye phytochromes show photoreversible changes in retention times, with the red absorbing form of phytochrome (Pr form) eluting later than the far red absorbing form of phytochrome produced by saturating red light illumination of Pr (Pfr form) in a variety of different mobile phase buffers. Molecular mass calibration with globular protein standards in Tris-glycol buffers provides estimates of 318-349 and 363-366 kDa for the molecular sizes of the Pr and Pfr forms, respectively. These analyses support earlier studies that phytochrome is a nonglobular homodimer of 124-kDa subunits in vitro. Limited proteolytic dissection of phytochrome in nondenaturing buffers with seven different endoproteases provides evidence for two "operational" domains within the 124-kDa subunit with molecular mass values of 69-72 and 52-55 kDa. The larger 69-72-kDa domain contains the site for the chromophore attachment as shown by gel electrophoresis derived enzyme-linked immunosorbent assay utilizing site-directed rabbit antiserum to a synthetic undecapeptide which is homologous with the chromophore binding site on oat phytochrome. This chromophore domain exhibits a compact structure, resistant to further proteolysis except near its N terminus. By contrast, the 52-55-kDa nonchromophore domain contains multiple sites for further proteolytic cleavage as revealed by rapid cleavage to smaller polypeptide fragments. Detailed kinetic analyses of the limited proteolytic cleavage of phytochrome with four endoproteases, subtilisin BPN', thermolysin, trypsin, and clostripain, has mapped specific regions within the 124-kDa subunit that participate in light-induced conformational changes. These include a 4-10-kDa region near the N terminus of the chromophore binding domain and at least two regions within the nonchromophore domain. A comprehensive peptide map of the oat phytochrome subunit is presented, which incorporates the results of these proteolytic studies with the recent, yet unpublished sequence analyses of Avena phytochrome cDNA clones which show the N-terminal localization of the chromophore binding site (Hershey, H. P., Colbert, J. T., Lissemore, J. L., Barker, R. F., and Quail, P. H. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 2332-2336).

Chromatography, High Pressure Liquid↗
PubMed2000

Arabidopsis phytochromes C and E have different spectral characteristics from those of phytochromes A and B.

The red/far-red light absorbing phytochromes play a major role as sensor proteins in photomorphogenesis of plants. In Arabidopsis the phytochromes belong to a small gene family of five members, phytochrome A (phyA) to E (phyE). Knowledge of the dynamic properties of the phytochrome molecules is the basis of phytochrome signal transduction research. Beside photoconversion and destruction, dark reversion is a molecular property of some phytochromes. A possible role of dark reversion is the termination of signal transduction. Since Arabidopsis is a model plant for biological and genetic research, we focussed on spectroscopic characterization of Arabidopsis phytochromes, expressed in yeast. For the first time, we were able to determine the relative absorption maxima and minima for a phytochrome C (phyC) as 661/725 nm and for a phyE as 670/724 nm. The spectral characteristics of phyC and E are strictly different from those of phyA and B. Furthermore, we show that both phyC and phyE apoprotein chromophore adducts undergo a strong dark reversion. Difference spectra, monitored with phycocyanobilin and phytochromobilin as the apoprotein's chromophore, and in vivo dark reversion of the Arabidopsis phytochrome apoprotein phycocyanobilin adducts are discussed with respect to their physiological function.

Apoproteins↗
PubMed1994

Phytochrome B and at Least One Other Phytochrome Mediate the Accelerated Flowering Response of Arabidopsis thaliana L. to Low Red/Far-Red Ratio.

We have investigated the involvement of phytochrome B in the early-flowering response of Arabidopsis thaliana L. seedlings to low red:far-red (R/FR) ratio light conditions. The phytochrome B-deficient hy3 (phyB) mutant is early flowering, and in this regard it resembles the shade-avoidance phenotype of its isogenic wild type. Seedlings carrying the hy2 mutation, resulting in a deficiency of phytochrome chromophore and hence of active phytochromes, also flower earlier than wild-type plants. Whereas hy3 or hy2 seedlings show only a slight acceleration of flowering in response to low R/FR ratio, seedlings that are doubly homozygous for both mutations flower earlier than seedlings carrying either phytochrome-related mutation alone. This additive effect clearly indicates the involvement of one or more phytochrome species in addition to phytochrome B in the flowering response as well as indicating the presence of some functional phytochrome B in hy2 seedlings. Seedlings that are homozygous for the hy3 mutation and one of the fca, fwa, or co late-flowering mutations display a pronounced early-flowering response to low R/FR ratio. A similar response to low R/FR ratio is displayed by seedlings doubly homozygous for the hy2 mutation and any one of the late-flowering mutations. Thus, placing the hy3 or hy2 mutations into a late-flowering background has the effect of uncovering a flowering response to low R/FR ratio. Seedlings that are triply homozygous for the hy3, hy2 mutations and a late-flowering mutation flower earlier than the double mutants and do not respond to low R/FR ratio. Thus, the observed flowering responses to low R/FR ratio in phytochrome B-deficient mutants can be attributed to the action of at least one other phytochrome species.

Journal Article↗
PubMed1980

Phytochrome Pelletability Induced by Irradiation in Vivo: TEST FOR IN VITRO BINDING OF ADDED [S]PHYTOCHROME.

Undegraded, highly purified [(35)S]phytochrome was immunoaffinity-purified either from dark control oat (cv. Garry) shoots or from etiolated oat shoots that were previously irradiated first with red and then with far-red light so that, if proper extraction conditions had been utilized, about 60% of the total phytochrome would have been pelletable. When [(35)S]phytochrome was added to extraction buffer immediately prior to homogenization of etiolated oat shoots, pelletability assays indicated that there was no preferential binding of [(35)S]phytochrome regardless of (a) whether it was purified from dark control or irradiated shoots, (b) whether it was added as phytochrome-red-absorbing form or phytochrome-far-red-absorbing form, or (c) whether it was added to dark control or red-irradiated shoots. Similarly, binding of [(35)S]phytochrome to resuspended pellets obtained from crude oat extracts was not specific for the source of [(35)S]phytochrome, for its form, or for the irradiation treatment given to intact shoots used to prepare the resuspended pellets. No evidence was obtained to support the hypothesis that phytochrome binds with specificity to particulate material in vitro under conditions used to assay for light-enhanced, in vivo-induced phytochrome pelletability.

Journal Article↗
PubMed1995

Phytochrome A overexpression in transgenic tobacco. Correlation of dwarf phenotype with high concentrations of phytochrome in vascular tissue and attenuated gibberellin levels.

Phytochromes are a family of related chromoproteins that regulate photomorphogenesis in plants. Ectopic overexpression of the phytochrome A in several plant species has pleiotropic effects, including substantial dwarfing, increased pigmentation, and delayed leaf senescence. We show here that the dwarf response is related to a reduction in active gibberellins (GAs) in tobacco (Nicotiana tabacum) overexpressing oat phytochrome A under the control of the cauliflower mosaic virus (CaMV) 35S promoter and can be suppressed by foliar applications of gibberellic acid. In transgenic seedlings, high concentrations of oat phytochrome A were detected in stem and petiole vascular tissue (consistent with the activity of the CaMV 35S promoter), implicating vascular tissue as a potential site of phytochrome A action. To examine the efficacy of this cellular site, oat phytochrome A was also expressed using Arabidopsis chlorophyll a/b-binding protein (CAB) and the Arabidopsis ubiquitin (UBQ1) promoters. Neither promoter was as effective as CaMV 35S in expressing phytochrome in vascular tissue or in inducing the dwarf phenotype. Collectively, these data indicate that the spatial distribution of ectopic phytochrome is important in eliciting the dwarf response and suggest that the phenotype is invoked by elevated levels of the far-red-absorbing form of phytochrome within vascular tissue repressing GA biosynthesis.

Arabidopsis Proteins↗
PubMed2005

Phytochrome-specific type 5 phosphatase controls light signal flux by enhancing phytochrome stability and affinity for a signal transducer.

Environmental light information such as quality, intensity, and duration in red (approximately 660 nm) and far-red (approximately 730 nm) wavelengths is perceived by phytochrome photoreceptors in plants, critically influencing almost all developmental strategies from germination to flowering. Phytochromes interconvert between red light-absorbing Pr and biologically functional far-red light-absorbing Pfr forms. To ensure optimal photoresponses in plants, the flux of light signal from Pfr-phytochromes should be tightly controlled. Phytochromes are phosphorylated at specific serine residues. We found that a type 5 protein phosphatase (PAPP5) specifically dephosphorylates biologically active Pfr-phytochromes and enhances phytochrome-mediated photoresponses. Depending on the specific serine residues dephosphorylated by PAPP5, phytochrome stability and affinity for a downstream signal transducer, NDPK2, were enhanced. Thus, phytochrome photoreceptors have developed an elaborate biochemical tuning mechanism for modulating the flux of light signal, employing variable phosphorylation states controlled by phosphorylation and PAPP5-mediated dephosphorylation as a mean to control phytochrome stability and affinity for downstream transducers.

Arabidopsis↗
PubMed1993

Analysis of genes negatively regulated by phytochrome action in Lemna gibba and identification of a promoter region required for phytochrome responsiveness.

As a step to understanding how the photoreceptor phytochrome acts to change the transcription of specific nuclear genes in Lemna gibba, we wish to compare promoter elements involved in negative regulation by phytochrome with those involved in positive regulation. We have isolated three genes negatively regulated by phytochrome, designated NR (negatively phytochrome regulated) genes (P.A. Okubara, E.M. Tobin [1991] Plant Physiol 96:1237-1245), and we have now sequenced two of these. The promoters of both contain some sequence motifs that are identical with motifs from other genes. We used a transient assay in L. gibba to demonstrate that approximately 1.7 kb pairs of the NPR1 promoter and 1.1 kb pairs of the NPR2 promoter could confer negative phytochrome regulation to a luciferase reporter gene. Deletion analysis of the NPR2 promoter showed that sequences between -208 and -82 from the transcription start were necessary for negative phytochrome regulation. However, this region was not sufficient to confer negative regulation by phytochrome to another promoter. Additionally, we noted that this region showed no similarity to a region identified as important for the negative regulation of the oat phyA promoter (W.B. Bruce, X.-W. Deng, P.H. Quail [1991] EMBO J 10:3015-3024), but it does contain a sequence element found in several other kinds of genes, including ones positively regulated by phytochrome. The deduced amino acid sequences of NPR1 and NPR2 were found to share similarities with many abscisic acid-induced or seed-abundant proteins. Thus, these genes, like other phytochrome-regulated genes, might respond to multiple regulatory signals.

Amino Acid Sequence↗
PubMed1970

Studies on phytochrome. Some properties of electrophoretically pure phytochrome.

1. Phytochrome was purified from etiolated oat (Avena sativa) seedlings either by gel-filtration chromatography and ion-exchange chromatography or by gel-filtration chromatography and calcium phosphate chromatography. Differences were observed in the spectral properties of phytochrome isolated by the two methods. 2. Electrophoresis of pure phytochrome at pH values between 9.0 and 6.0 showed the tendency of phytochrome to form different molecular species. Studies in the ultracentrifuge did not show a corresponding change in the sedimentation coefficient with the change in pH. 3. Tryptic digestion of electrophoretically pure phytochrome gave 17 peptides and a photoactive core. The amino acid composition of the core is reported and compared with the analysis of whole phytochrome. 4. Some properties of phytochrome isolated from Pisum sativum are compared with those of phytochrome from A. sativa. 5. The properties of phytochrome purified by other workers are compared with our findings.

Amino Acids↗