Background-suppressed tumor-targeted photoacoustic imaging using bacterial carriers.

Photoacoustic (PA) imaging offers promise for biomedical applications due to its ability to image deep within biological tissues while providing detailed molecular information; however, its detection sensitivity is limited by high background signals that arise from endogenous chromophores. Genetic reporter proteins with photoswitchable properties enable the removal of background signals through the subtraction of PA images for each light-absorbing form. Unfortunately, the application of photoswitchable chromoproteins for tumor-targeted imaging has been hampered by the lack of an effective targeted delivery scheme; that is, photoswitchable probes must be delivered in vivo with high targeting efficiency and specificity. To overcome this limitation, we have developed a tumor-targeting delivery system in which tumor-homing bacteria (Escherichia coli) are exploited as carriers to affect the point-specific delivery of genetically encoded photochromic probes to the tumor area. To improve the efficiency of the desired background suppression, we engineered a phytochrome-based reporter protein (mDrBphP-PCMm/F469W) that displays higher photoswitching contrast than those in the current state of the art. Photoacoustic computed tomography was applied to achieve good depth and resolution in the context of in vivo (mice) imaging. The present system effectively integrates a genetically encoded phytochrome-based reporter protein, PA imaging, and synthetic biology (GPS), to achieve essentially background-suppressed tumor-targeted PA monitoring in deep-seated tissues. The ability to image tumors at substantial depths may enable target-specific cancer diagnoses to be made with greater sensitivity, fidelity, and specificity.

Coregulation of gene expression by White collar 1 and phytochrome in Ustilago maydis.

Ustilago maydis encodes ten predicted light-sensing proteins. The biological functions of only a few of them are elucidated. Among the characterized ones are two DNA-photolyases and two rhodopsins that act as DNA-repair enzymes or green light-driven proton pumps, respectively. Here we report on the role of two other photoreceptors in U. maydis, namely White collar 1 (Wco1) and Phytochrome 1 (Phy1). We show that they bind flavins or biliverdin as chromophores, respectively. Both photoreceptors undergo a photocycle in vitro. Wco1 is the dominant blue light receptor in the saprophytic phase, controlling all of the 324 differentially expressed genes in blue light. U. maydis also responds to red and far-red light. However, the number of red or far-red light-controlled genes is less compared to blue light-regulated ones. Moreover, most of the red and far-red light-controlled genes not only depend on Phy1 but also on Wco1, indicating partial coregulation of gene expression by both photoreceptors. GFP-fused Wco1 is preferentially located in the nucleus, Phy1 in the cytosol, thus providing no hint that these photoreceptors directly interact or operate within the same complex. This is the first report on a functional characterization and coaction of White collar 1 and phytochrome orthologs in basidiomycetes.

GAF-CaMP3-sfGFP, An Enhanced Version of the Near-Infrared Genetically Encoded Positive Phytochrome-Based Calcium Indicator for the Visualization of Neuronal Activity.

The first generation of near-infrared, genetically encoded calcium indicators (NIR-GECIs) was developed from bacterial phytochrome-based fluorescent proteins that utilize biliverdin (BV) as the chromophore moiety. However, NIR-GECIs have some main drawbacks such as either an inverted response to calcium ions (in the case of NIR-GECO1) or a limited dynamic range and a lack of data about their application in neurons (in the case of GAF-CaMP2-superfolder green fluorescent protein (sfGFP)). Here, we developed an enhanced version of the GAF-CaMP2-sfGFP indicator, named GAF-CaMP3-sfGFP. The GAF-CaMP3-sfGFP demonstrated spectral characteristics, molecular brightness, and a calcium affinity similar to the respective characteristics for its progenitor, but a 2.9-fold larger DF/F response to calcium ions. As compared to GAF-CaMP2-sfGFP, in cultured HeLa cells, GAF-CaMP3-sfGFP had similar brightness but a 1.9-fold larger DF/F response to the elevation of calcium ions levels. Finally, we successfully utilized the GAF-CaMP3-sfGFP for the monitoring of the spontaneous and stimulated activity of neuronal cultures and compared its performance with the R-GECO1 indicator using two-color confocal imaging. In the cultured neurons, GAF-CaMP3-sfGFP showed a linear DF/F response in the range of 0-20 APs and in this range demonstrated a 1.4-fold larger DF/F response but a 1.3- and 2.4-fold slower rise and decay kinetics, respectively, as compared to the same parameters for the R-GECO1 indicator.

Characterization of a novel cotton MYB gene, GhMYB108-like responsive to abiotic stresses.

Transcriptional factors are the major regulators of plant signaling pathways in response to environmental stresses i.e., drought, salinity and cold. Hereby, the GhMYB108-like was characterized to determine whether it regulate these stresses. The GhMYB108-like cDNA consisted of 1107 base pairs (bp) with 807 open reading frame encoded a protein of 268 amino acids. Its isoelectric point and molecular weight are 5.51 and 30.3 kDa respectively. Phylogenetic analysis and online databases revealed that GhMYB108-like proteins are closely related with the Arabidopsis thaliana MYB2. Important cis-elements were detected in the promotor region of GhMYB108-like responding to stresses and phytohormones. The 3D structure of GhMYB108-like protein has been predicted. In addition, various physico-chemical properties of GhMYB108-like have been determined. Subcellular localization confirmed that GhMYB108-like are nuclear localized protein. Quantitative expression analysis showed that polyethylene glycol and salt treatments significantly induced the expression of GhMYB108-like. Overall, our findings suggest that GhMYB108-like is an important gene that would plays important regulatory role in response to drought and salt stresses.

Focusing light inside live tissue using reversibly switchable bacterial phytochrome as a genetically encoded photochromic guide star.

Focusing light deep by engineering wavefronts toward guide stars inside scattering media has potential biomedical applications in imaging, manipulation, stimulation, and therapy. However, the lack of endogenous guide stars in biological tissue hinders its translations to in vivo applications. Here, we use a reversibly switchable bacterial phytochrome protein as a genetically encoded photochromic guide star (GePGS) in living tissue to tag photons at targeted locations, achieving light focusing inside the tissue by wavefront shaping. As bacterial phytochrome-based GePGS absorbs light differently upon far-red and near-infrared illumination, a large dynamic absorption contrast can be created to tag photons inside tissue. By modulating the GePGS at a distinctive frequency, we suppressed the competition between GePGS and tissue motions and formed tight foci inside mouse tumors in vivo and acute mouse brain tissue, thus improving light delivery efficiency and specificity. Spectral multiplexing of GePGS proteins with different colors is an attractive possibility.

Phytohormone priming elevates the accumulation of defense-related gene transcripts and enhances bacterial blight disease resistance in cassava.

Cassava bacterial blight (CBB) disease caused by Xanthomonas axonopodis pv. manihotis (Xam) is a severe disease in cassava worldwide. In addition to causing significant cassava yield loss, CBB disease has not been extensively studied, especially in terms of CBB resistance genes. The present research demonstrated the molecular mechanisms underlining the defense response during Xam infection in two cassava cultivars exhibiting different degrees of disease resistance, Huay Bong60 (HB60) and Hanatee (HN). Based on gene expression analysis, ten of twelve putative defense-related genes including, leucine-rich repeat receptor-like kinases (LRR-RLKs), resistance (R), WRKY and pathogenesis-related (PR) genes, were differentially expressed between these two cassava cultivars during Xam infection. The up-regulation of defense-related genes observed in HB60 may be the mechanism required for the reduction of disease severity in the resistant cultivar. Interestingly, priming with salicylic acid (SA) or methyl jasmonate (MeJA) for 24 h before Xam inoculation could enhance the defense response in both cassava cultivars. The disease severity was decreased 10% in the resistant cultivar (HB60) and was remarkably reduced 21% in the susceptible cultivar (HN) by SA/MeJA priming. Priming with Xam inoculation modulated cassava4.1_013417, cassava4.1_030866 and cassava4.1_020555 (highest similarity to MeWRKY59, MePR1 and AtPDF2.2, respectively) expression and led to enhanced resistance of the susceptible cultivar in the second infection. The putative cis-regulatory elements were predicted in an upstream region of these three defense-related genes. The different gene expression levels in these genes between the two cultivars were due to the differences in cis-regulatory elements in their promoter regions. Taken together, our study strongly suggested that the induction of defense-related genes correlated with defense resistance against Xam infection, and exogenous application of SA or MeJA could elevate the defense response in both cultivars of cassava. This finding should pave the way for management to reduce yield loss from disease and genetic improvement in cassava.

Beneficial nutraceutical modulation of cerebral erythropoietin expression and oxidative stress: an experimental study.

The main object of this study is to examine the effect of Klamin®, a nutraceutical containing phenylethylamine, phycocyanins, mycosporine-like aminoacids and aphanizomenon flos aquae-phytochrome on the learning and memory ability, the oxidative status and cerebral erythropoietin and its receptor EPO/EPOR system in prematurely senescent (PS) mice. A total of 28 PS mice, selected according to a prior T-maze test, and 26 non-prematurely senescent mice (NPS) mice were chosen. PS animals were divided into 3 groups and followed for 4 weeks: A) normal chow diet; B) added with Klamin® at 20 mg/kg/day (low dose); C) added with Klamin® at 100mg/kg/day (high dose). A further group of NPS mice given either normal food (group D) or high dose Klamin® (group E) was also considered. The behavioral procedures of spatial learning ability (Morris test) showed that PS mice had significantly longer learning time as compared to their NPS counterpart (p<0.01), but this effect was prevented especially in mice supplemented with high-dose Klamin® (p<0.05) which improved performances in NPS mice (p<0.05). High-dose Klamin® supplementation restored the depleted total thiol concentration in the brain observed in PS mice while normalizing their increased malonildialdehyde level (p<0.05). Moreover, the high-dosage only caused a significant upregulation of EPO/EPOR system both in PS and in NPS animals (p<0.05). Taken together, these data suggest that this specific alga Klamath extract has considerable antioxidant and adaptogenic properties, also through a stimulatory effect of cerebral EPO/EPO system.

PIF genes mediate the effect of sucrose on seedling growth dynamics.

As photoautotrophs, plants can use both the form and amount of fixed carbon as a measure of the light environment. In this study, we used a variety of approaches to elucidate the role of exogenous sucrose in modifying seedling growth dynamics. In addition to its known effects on germination, high-resolution temporal analysis revealed that sucrose could extend the number of days plants exhibited rapid hypocotyl elongation, leading to dramatic increases in ultimate seedling height. In addition, sucrose changed the timing of daily growth maxima, demonstrating that diel growth dynamics are more plastic than previously suspected. Sucrose-dependent growth promotion required function of multiple phytochrome-interacting factors (PIFs), and overexpression of PIF5 led to growth dynamics similar to plants exposed to sucrose. Consistent with this result, sucrose was found to increase levels of PIF5 protein. PIFs have well-established roles as integrators of response to light levels, time of day and phytohormone signaling. Our findings strongly suggest that carbon availability can modify the known photomorphogenetic signaling network.

ELF4 is a phytochrome-regulated component of a negative-feedback loop involving the central oscillator components CCA1 and LHY.

Evidence has been presented that a negative transcriptional feedback loop formed by the genes CIRCADIAN CLOCK ASSOCIATED (CCA1), LATE ELONGATED HYPOCOTYL (LHY) and TIMING OF CAB (TOC1) constitutes the core of the central oscillator of the circadian clock in Arabidopsis. Here we show that these genes are expressed at constant, basal levels in dark-grown seedlings. Transfer to constant red light (Rc) rapidly induces a biphasic pattern of CCA1 and LHY expression, and a reciprocal TOC1 expression pattern over the first 24 h, consistent with initial induction of this synchronous oscillation by the light signal. We have used this assay with wild-type and mutant seedlings to examine the role of these oscillator components, and to determine the function of ELF3 and ELF4 in their light-regulated expression. The data show that whereas TOC1 is necessary for light-induced CCA1/LHY expression, the combined absence of CCA1 and LHY has little effect on the pattern of light-induced TOC1 expression, indicating that the negative regulatory arm of the proposed oscillator is not fully functional during initial seedling de-etiolation. By contrast, ELF4 is necessary for light-induced expression of both CCA1 and LHY, and conversely, CCA1 and LHY act negatively on light-induced ELF4 expression. Together with the observation that the temporal light-induced expression profile of ELF4 is counter-phased to that of CCA1 and LHY and parallels that of TOC1, these data are consistent with a previously unrecognized negative-feedback loop formed by CCA1/LHY and ELF4 in a manner analogous to the proposed CCA1/LHY/TOC1 oscillator. ELF3 is also necessary for light-induced CCA1/LHY expression, but it is neither light-induced nor clock-regulated during de-etiolation. Taken together, the data suggest (a) that ELF3, ELF4, and TOC1 all function in the primary, phytochrome-mediated light-input pathway to the circadian oscillator in Arabidopsis; and (b) that this oscillator consists of two or more interlocking transcriptional feedback loops that may be differentially operative during initial light induction and under steady-state circadian conditions in entrained green plants.

HFR1, a putative bHLH transcription factor, mediates both phytochrome A and cryptochrome signalling.

Plants are very sensitive to their light environment. They use cryptochromes and phytochromes to scan the light spectrum. Those two families of photoreceptors mediate a number of similar physiological responses. The putative bHLH (basic Helix Loop Helix) transcription factor long hypocotyl in far-red (HFR1) is important for a subset of phytochrome A (phyA)-mediated light responses. Interestingly, hfr1 alleles also have reduced de-etiolation responses, including hypocotyl growth, cotyledon opening and anthocyanin accumulation, when grown in blue light. This phenotype is particularly apparent under high fluence rates. The analysis of double mutants between hfr1 and different blue light photoreceptor mutants demonstrates that, in addition to its role in phyA signalling, HFR1 is a component of cryptochrome 1 (cry1)-mediated light signalling. Moreover, HFR1 mRNA levels are high both in blue and in far-red light but low in red light. These results identify HFR1 as a positively acting component of cry1 signalling and indicate that HFR1 integrates light signals from both phyA and cry1.

The Arabidopsis COG1 gene encodes a Dof domain transcription factor and negatively regulates phytochrome signaling.

Light is a critical environmental factor that influences almost all developmental aspects of plants, including seed germination, seedling morphogenesis, and transition to reproductive growth. Plants have therefore developed an intricate network of mechanisms to perceive and process environmental light information. To further characterize the molecular basis of light-signaling processes in plants, we screened an activation tagging pool of Arabidopsis for altered photoresponses. A dominant mutation, cog1-D, attenuated various red (R) and far-red (FR) light-dependent photoresponses. The mutation was caused by overexpression of a gene encoding a member of the Dof family of transcription factors. The photoresponses in Arabidopsis were inversely correlated with the expression levels of COG1 mRNA. When the COG1 gene was overexpressed in transgenic plants, the plants exhibited hyposensitive responses to R and FR light in a manner inversely dependent on COG1 mRNA levels. On the other hand, transgenic lines expressing antisense COG1 were hypersensitive to R and FR light. Expression of the COG1 gene is light inducible and requires phytochrome A (phyA) for FR light-induced expression and phytochrome B (phyB) for R light-induced expression. Thus, the COG1 gene functions as a negative regulator in both the phyA- and phyB-signaling pathways. We suggest that these phytochromes positively regulate the expression of COG1, a negative regulator, as a mechanism for fine tuning the light-signaling pathway.

Light-signalling pathways leading to the co-ordinated expression of HEMA1 and Lhcb during chloroplast development in Arabidopsis thaliana.

During de-etiolation, the co-ordinated synthesis of chlorophyll and the chlorophyll a/b-binding proteins is critical to the development of functional light-harvesting complexes. To understand how this co-ordination is achieved, we have made a detailed study of the light-regulated signalling pathways mediating the expression of the HEMA1 and Lhcb genes encoding glutamyl-tRNA reductase, the first committed enzyme of 5-aminolaevulinic acid formation, and chlorophyll a/b-binding proteins, respectively. To do this, we have screened 7 photoreceptor and 12 light-signalling mutants of Arabidopsis thaliana L. for induction of HEMA1 and Lhcb expression in continuous red, far-red and blue light and following a red pulse. We have categorised these mutants into two groups. The phyA, phyB, phyAphyB, cry1, cry2, cop1, det1, poc1, eid1, and far1 mutations lead to diverse effects on the light regulation of HEMA1, but affect Lhcb expression to a similar degree. The hy1, hy2, hy5, fin219, fhy1, fhy3, spa1, ndpk2, and pat1 mutants also affect light regulation of both HEMA1 and Lhcb expression, but with differences in the relative magnitude of the two responses. The fhy1 and fhy3 mutants show the most significant differences in light regulation between the two genes, with both showing a strong inhibition of HEMA1 expression under continuous red light. These results demonstrate that co-ordinated regulation of HEMA1 and Lhcb is largely achieved through parallel light regulation mediated by shared phytochrome- and cryptochrome-signalling pathways. However, glutamyl-tRNA reductase is also required for the synthesis of other tetrapyrroles and this dual role may account for the observed differences in these light-signalling pathways.

HFR1, a phytochrome A-signalling component, acts in a separate pathway from HY5, downstream of COP1 in Arabidopsis thaliana.

HFR1, a basic helix-loop-helix protein, is known to be required for a subset of phytochrome A (phyA)-dependent photoresponses. To investigate the role of HFR1 in light signalling, we have examined the genetic interaction between HFR1 and HY5, a positive regulator of light signalling, and COP1, a repressor of photomorphogenesis. Double mutant analysis suggests that HFR1 mediates phyA-dependent inhibition of hypocotyl elongation independently of HY5. HFR1 was shown to be necessary for a subset of cop1-triggered photomorphogenic phenotypes in the dark, including inhibition of hypocotyl elongation, gravitropic hypocotyl growth, and expression of the light-inducible genes CAB and RBCS. Phenotypic analysis of the triple mutant cop1hy5hfr1 indicated that both HFR1 and HY5 are required for cop1-mediated photomorphogenic seedling development in darkness, consistent with their additive roles in phyA-dependent signalling. Taken together, these results suggest that HFR1 might act downstream of COP1, in a separate pathway from HY5, to mediate photomorphogenesis in Arabidopsis.

Negative interference of endogenous phytochrome B with phytochrome A function in Arabidopsis.

To study negative interactions between phytochromes, phytochrome B (phyB) overexpressor lines, the mutants phyA-201, phyB-4, phyB-5, phyD-1, phyA-201 phyB-5, phyA-201 phyD-1, and phyB-5 phyD-1 of Arabidopsis were used. Endogenous phyB, but not phytochrome D (phyD), partly suppressed phytochrome A (phyA)-dependent inhibition of hypocotyl elongation in far-red light (FR). Dichromatic irradiation demonstrated that the negative effect of phyB was largely independent of the photoequilibrium, i.e. far-red light absorbing form of phytochrome formation. Moreover, phyB-4, a mutant impaired in signal transduction, did not show a loss of inhibition of phyA by phyB. Overexpression of phyB, conversely, resulted in an enhanced inhibition of phyA function, even in the absence of supplementary carbohydrates. However, overexpression of a mutated phyB, which cannot incorporate the chromophore, had no detectable effect on phyA action. In addition to seedling growth, accumulation of anthocyanins in FR, another manifestation of the high irradiance response, was strongly influenced by phyB holoprotein. Induction of seed germination by FR, a very low fluence response, was suppressed by both endogenous phyB and phyD. In conclusion, we show that both classical response modes of phyA, high irradiance response, and very low fluence response are subject to an inhibitory action of phyB-like phytochromes. Possible mechanisms of the negative interference are discussed.

GIGANTEA is a nuclear protein involved in phytochrome signaling in Arabidopsis.

In a genetic screen of available T-DNA-mutagenized Arabidopsis populations for loci potentially involved in phytochrome (phy) signaling, we identified a mutant that displayed reduced seedling deetiolation under continuous red light, but little if any change in responsiveness to continuous far-red light. This behavior suggests disruption of phyB, but not phyA signaling. We have cloned the mutant locus by using the T-DNA insertion and found that the disrupted gene is identical to the recently described GIGANTEA (GI) gene identified as being involved in control of flowering time. The encoded GI polypeptide has no sequence similarity to any known proteins in the database. However, by using beta-glucuronidase-GI and green fluorescent protein-GI fusion constructs, we have shown that GI is constitutively targeted to the nucleus in transient transfection assays. Optical sectioning by using the green fluorescent protein-GI fusion protein showed green fluorescence throughout the nucleoplasm. Thus, contrary to previous computer-based predictions that GI would be an integral plasma membrane-localized polypeptide, the data here indicate that it is a nucleoplasmically localized protein. This result is consistent with the proposed role in phyB signaling, given recent evidence that early phy signaling events are nuclear localized.

Phytochrome regulates gibberellin biosynthesis during germination of photoblastic lettuce seeds.

Germination of lettuce (Lactuca sativa L.) seed is regulated by phytochrome. The requirement for red light is circumvented by the application of gibberellin (GA). We have previously shown that the endogenous content of GA1, the main bioactive GA in lettuce seeds, increases after red-light treatment. To clarify which step of GA1 synthesis is regulated by phytochrome, cDNAs encoding GA 20-oxidases (Ls20ox1 and Ls20ox2, for L. sativa GA 20-oxidase) and 3beta-hydroxylases (Ls3h1 and Ls3h2 for L. sativa GA 3beta-hydroxylase) were isolated from lettuce seeds by reverse-transcription polymerase chain reaction. Functional analysis of recombinant proteins expressed in Escherichia coli confirmed that the Ls20ox and Ls3h encode GA 20-oxidases and 3beta-hydroxylases, respectively. Northern-blot analysis showed that Ls3h1 expression was dramatically induced by red-light treatment within 2 h, and that this effect was canceled by a subsequent far-red-light treatment. Ls3h2 mRNA was not detected in seeds that had been allowed to imbibe under any light conditions. Expression of the two Ls20ox genes was induced by initial imbibition alone in the dark. The level of Ls20ox2 mRNA decreased after the red-light treatment, whereas that of Ls20ox1 was unaffected by light. These results suggest that red light promotes GA1 synthesis in lettuce seeds by inducing Ls3h1 expression via phytochrome action.

Abscisic acid signaling through cyclic ADP-ribose in plants.

Abscisic acid (ABA) is the primary hormone that mediates plant responses to stresses such as cold, drought, and salinity. Single-cell microinjection experiments in tomato were used to identify possible intermediates involved in ABA signal transduction. Cyclic ADP-ribose (cADPR) was identified as a signaling molecule in the ABA response and was shown to exert its effects by way of calcium. Bioassay experiments showed that the amounts of cADPR in Arabidopsis thaliana plants increased in response to ABA treatment and before ABA-induced gene expression.

The interaction of light and abscisic acid in the regulation of plant gene expression.

Extended dark treatments of light-grown plants of both Lemna gibba and Arabidopsis thaliana resulted in substantial increases in abscisic acid (ABA) concentrations. The concentration of ABA could be negatively regulated by phytochrome action in Lemna. As has been noted in other species, ABA treatment reduced Lemna rbcS and Lhcb RNA levels, which are positively regulated by phytochrome in many species. In view of these observations, the possibility that phytochrome effects on gene expression may be mediated primarily by changes in ABA was tested using a transient assay in intact plants. The phytochrome responsiveness of the Lemna Lhcb2*1 promoter was still apparent in the presence of exogenous ABA. Additionally, when 2-bp mutations were introduced into this promoter so that phytochrome responsiveness was lost, a response to exogenous ABA was still present. We conclude that phytochrome- and ABA-response elements are separable in the Lhcb2*1 promoter. We tested whether the effects of ABA on RNA abundance could be inhibited by treatment with gibberellin and found no evidence for such an inhibition. We have also found that the ABA-responsive Em promoter of wheat can be negatively regulated by phytochrome action. It is likely that this regulation is mediated at least in part by phytochrome-induced changes in ABA levels. Our results demonstrate that it is essential to take into account that dark treatments and the phytochrome system can affect ABA levels when interpreting studies of light-regulated genes.

Functional dissection of circadian clock- and phytochrome-regulated transcription of the Arabidopsis CAB2 gene.

Both the circadian clock and phytochrome regulate expression of the Arabidopsis genes encoding the light-harvesting chlorophyll a/b-binding proteins (CAB genes). Phytochrome activates CAB transcription, and it has been proposed that the circadian clock negatively regulates CAB transcription. The tobacco nuclear proteins CUF-1 (CAB upstream factor 1) and CGF-1 (CAB GATA factor 1) bind the Arabidopsis CAB2 promoter, and the CGF-1 binding site is contained within a minimal clock- and phytochrome-regulated region of the promoter. We have used in vivo cab2::luciferase gene bioluminescence markers containing site-directed mutations in the CUF-1 and CGF-1 binding sites to define the role of these proteins in CAB2 regulation and to further delineate the terminal genomic targets of the phytochrome and circadian clock signal transduction pathways. Results from these studies confirm that CUF-1 is not required to generate the circadian clock- or phytochrome-responsive CAB2 expression pattern but rather functions as a positive factor to increase CAB2 expression levels. CGF-1 interaction with the CAB2 promoter mediates the acute increase in CAB2 expression in response to phytochrome activation and contributes to the light-induced high-amplitude circadian oscillation in CAB2 expression.