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A Nagatani

Publications and source records attributed to A Nagatani.

At least 19 recordsLinked to original sources
PubMed2001

Arabidopsis genomes uncoupled 5 (GUN5) mutant reveals the involvement of Mg-chelatase H subunit in plastid-to-nucleus signal transduction.

A plastid-derived signal plays an important role in the coordinated expression of both nuclear- and chloroplast-localized genes that encode photosynthesis-related proteins. Arabidopsis GUN (genomes uncoupled) loci have been identified as components of plastid-to-nucleus signal transduction. Unlike wild-type plants, gun mutants have nuclear Lhcb1 expression in the absence of chloroplast development. We observed a synergistic phenotype in some gun double-mutant combinations, suggesting there are at least two independent pathways in plastid-to-nucleus signal transduction. There is a reduction of chlorophyll accumulation in gun4 and gun5 mutant plants, and a gun4gun5 double mutant shows an albino phenotype. We cloned the GUN5 gene, which encodes the ChlH subunit of Mg-chelatase. We also show that gun2 and gun3 are alleles of the known photomorphogenic mutants, hy1 and hy2, which are required for phytochromobilin synthesis from heme. These findings suggest that certain perturbations of the tetrapyrrole biosynthetic pathway generate a signal from chloroplasts that causes transcriptional repression of nuclear genes encoding plastid-localized proteins. The comparison of mutant phenotypes of gun5 and another Mg-chelatase subunit (ChlI) mutant suggests a specific function for ChlH protein in the plastid-signaling pathway.

Amino Acid Sequence↗
PubMed2000

Isolation and characterization of an Arabidopsis mutant, fireworks (fiw), which exhibits premature cessation of inflorescence growth and early leaf senescence.

To examine the mechanism underlying the reproductive development in monocarpic plants, we screened for mutants that exhibit premature cessation of inflorescence growth in Arabidopsis. We identified a novel mutant line that exhibited earlier cessation of flower formation and inflorescence stem elongation. This mutant also exhibited accelerated rosette leaf senescence after the cessation of the inflorescence growth. We designated the mutant fireworks (fiw) because flowers and siliques were clustered at the top of the fiw inflorescence. The fiw mutation was a single, recessive mutation and mapped on the lower part of chromosome 4. The fiw phenotype was not observable during vegetative growth, but the inflorescence growth was arrested more than 7 d earlier than the wild type (WT). Microscopic observation revealed that the fiw apical meristem was structurally preserved. The premature arrest of growth was observed not only in the primary inflorescence but also in the lateral inflorescence, which is consistent with the global proliferative arrest observed later in WT. Regardless of such dramatic phenotypic features, the fiw plants bore normal flowers and set fully matured siliques.

Arabidopsis↗
PubMed2000

Light-induced nuclear translocation of endogenous pea phytochrome A visualized by immunocytochemical procedures.

Although the physiological functions of phytochrome A (PhyA) are now known, the distribution of endogenous PhyA has not been examined. We have visualized endogenous PhyA apoprotein (PHYA) by immunolabeling cryosections of pea tissue, using PHYA-deficient mutants as negative controls. By this method, we examined the distribution of PHYA in different tissues and changes in its intracellular distribution in response to light. In apical hook cells of etiolated seedlings, PHYA immunolabeling was distributed diffusely in the cytosol. Exposure to continuous far-red (cFR) light caused a redistribution of the immunolabeling to the nucleus, first detectable after 1.5 hr and greatest at 4.5 hr. During this time, the amounts of spectrally active phytochrome and PHYA did not decline substantially. Exposure to continuous red (cR) light or to a brief pulse of red light also resulted in redistribution of immunolabeling to the nucleus, but this occurred much more rapidly and with a different pattern of intranuclear distribution than it did in response to cFR light. Exposures to cR light resulted in loss of immunolabeling, which was associated with PHYA degradation. These results indicate that the light-induced intracellular location of PHYA is wavelength dependent and imply that this is important for PhyA activity.

Biological Transport↗
PubMed1999

Light-dependent translocation of a phytochrome B-GFP fusion protein to the nucleus in transgenic Arabidopsis.

Phytochrome is a ubiquitous photoreceptor of plants and is encoded by a small multigene family. We have shown recently that a functional nuclear localization signal may reside within the COOH-terminal region of a major member of the family, phytochrome B (phyB) (Sakamoto, K., and A. Nagatani. 1996. Plant J. 10:859-868). In the present study, a fusion protein consisting of full-length phyB and the green fluorescent protein (GFP) was overexpressed in the phyB mutant of Arabidopsis to examine subcellular localization of phyB in intact tissues. The resulting transgenic lines exhibited pleiotropic phenotypes reported previously for phyB overexpressing plants, suggesting that the fusion protein is biologically active. Immunoblot analysis with anti-phyB and anti-GFP monoclonal antibodies confirmed that the fusion protein accumulated to high levels in these lines. Fluorescence microscopy of the seedlings revealed that the phyB-GFP fusion protein was localized to the nucleus in light grown tissues. Interestingly, the fusion protein formed speckles in the nucleus. Analysis of confocal optical sections confirmed that the speckles were distributed within the nucleus. In contrast, phyB-GFP fluorescence was observed throughout the cell in dark-grown seedlings. Therefore, phyB translocates to specific sites within the nucleus upon photoreceptor activation.

Arabidopsis↗
PubMed1999

Regulation of phytochrome B signaling by phytochrome A and FHY1 in Arabidopsis thaliana.

Phytochrome A (phyA) and phytochrome B (phyB) share the control of many processes but little is known about mutual signaling regulation. Here, we report on the interactions between phyA and phyB in the control of the activity of an Lhcb1*2 gene fused to a reporter, hypocotyl growth and cotyledon unfolding in etiolated Arabidopsis thaliana. The very-low fluence responses (VLFR) induced by pulsed far-red light and the high-irradiance responses (HIR) observed under continuous far-red light were absent in the phyA and phyA phyB mutants, normal in the phyB mutant, and reduced in the fhy1 mutant that is defective in phyA signaling. VLFR were also impaired in Columbia compared to Landsberg erecta. The low-fluence responses (LFR) induced by red-light pulses and reversed by subsequent far-red light pulses were small in the wild type, absent in phyB and phyA phyB mutants but strong in the phyA and fhy1 mutants. This indicates a negative effect of phyA and FHY1 on phyB-mediated responses. However, a pre-treatment with continuous far-red light enhanced the LFR induced by a subsequent red-light pulse. This enhancement was absent in phyA, phyB, or phyA phyB and partial in fhy1. The levels of phyB were not affected by the phyA or fhy1 mutations or by far-red light pre-treatments. We conclude that phyA acting in the VLFR mode (i.e. under light pulses) is antagonistic to phyB signaling whereas phyA acting in the HIR mode (i.e. under continuous far-red light) operates synergistically with phyB signaling, and that both types of interaction require FHY1.

Arabidopsis↗
PubMed1999

Plastidic RNA polymerase sigma factors in Arabidopsis.

In plant cells, plastid DNA is transcribed by at least two types of RNA polymerase, plastid-encoded RNA polymerase (PEP) and nuclear-encoded RNA polymerase (NEP). PEP is homologous to eubacterial transcription machinery, but its regulatory subunit, sigma (sigma) factor, is not encoded on the plastid DNA. We previously cloned the three nuclear-encoded sigma factor genes from Arabidopsis thaliana and designated them as sigA, sigB, and sigC. By means of RFLP mapping, sigA and sigB were mapped on chromosome I and sigC on the chromosome III. Based on comparison of the genomic structure of the three sig genes, intron sites in the 3' half of the genes were shown to be identical between sigB and sigC but divergent in sigA, consistent with the phylogenetic relevance of the three gene products. A transient expression assay of GFP fusions in Arabidopsis protoplasts showed that the N-termini of all three sig gene products functioned as chloroplast-targeting signals. We also constructed transgenic Arabidopsis lines harboring the sigA-promoter or the sigB-promoter uidA fusion. Both the sigA- and sigB-promoters were similarly activated at cotyledons, hypocotyls, rosette leaves, cauline leaves, sepals, and siliques but not at roots, seeds, or other flower organs. In addition, the two promoters were repeatedly activated in young seedlings under continuous light, possibly in an oscillated fashion.

Amino Acid Sequence↗
PubMed1998

Regulated nuclear targeting.

Extracellular signals are transduced to the nucleus through respective signal transduction pathways. Evidence in animals and yeast indicates the importance of regulated nuclear targeting in these processes. Although little is known about plants in this regard, some plant signaling factors have recently been shown to translocate to the nucleus upon receipt of a signal.

Animals↗
PubMed1998

An Arabidopsis mutant hypersensitive to red and far-red light signals.

A new mutant called psi2 (for phytochrome signaling) was isolated by screening for elevated activity of a chlorophyll a/b binding protein-luciferase (CAB2-LUC) transgene in Arabidopsis. This mutant exhibited hypersensitive induction of CAB1, CAB2, and the small subunit of ribulose-1,5-bisphosphate carboxylase (RBCS) promoters in the very low fluence range of red light and a hypersensitive response in hypocotyl growth in continuous red light of higher fluences. In addition, at high- but not low-light fluence rates, the mutant showed light-dependent superinduction of the pathogen-related protein gene PR-1a and developed spontaneous necrotic lesions in the absence of any pathogen. Expression of genes responding to various hormone and environmental stress pathways in the mutant was not significantly different from that of the wild type. Analysis of double mutants demonstrated that the effects of the psi2 mutation are dependent on both phytochromes phyA and phyB. The mutation is recessive and maps to the bottom of chromosome 5. Together, our results suggest that PSI2 specifically and negatively regulates both phyA and phyB phototransduction pathways. The induction of cell death by deregulated signaling pathways observed in psi2 is reminiscent of retinal degenerative diseases in animals and humans.

Arabidopsis↗
PubMed1997

Characterization of three cDNA species encoding plastid RNA polymerase sigma factors in Arabidopsis thaliana: evidence for the sigma factor heterogeneity in higher plant plastids.

By database search analysis, we identified three Arabidopsis EST (Expression Sequence Tag) entries having similarity to eubacterial RNA polymerase sigma factors. cDNA clones corresponding to these partial sequences were isolated, and the complete nucleotide sequences were determined. All three sequences encode proteins highly homologous to cyanobacterial and plastid sigma factors, and the gene products have N-terminal extensions which are assumed to function as plastid-targeting transit peptides. Thus we have concluded that the gene products are RNA polymerase sigma factors of plastids, and named sigA, sigB and sigC, respectively. Expression of these genes was analyzed by RNA gel-blot analysis and shown to be induced by illumination after a short-term dark adaptation. This strongly suggests that light regulation of the nuclear encoded sigma factor genes is involved in light-dependent activation of plastid promoters.

Amino Acid Sequence↗
PubMed1997

Photoresponses of transgenic Arabidopsis overexpressing the fern Adiantum capillus-veneris PHY1.

The phytochrome gene (PHY1) cDNA from the fern Adiantum capillus-veneris encodes an amino acid sequence that shows equal similarity (50-60%) to all five Arabidopsis phytochromes (PHYA-E). The A. capillus-veneris PHY1 cDNA was transformed into Arabidopsis ecotype Landsberg erecta to investigate its activity in angiosperms. Three of the resulting lines contained at least 8 times more spectrally active phytochrome than the wild type, indicating that A. capillus-veneris phytochrome can incorporate the chromophore of the host plants. Hypocotyl growth inhibition of these transgenic lines was investigated under red and far-red light. The results indicated dominant negative activity of A. capillus-veneris phy1 on the phytochrome A response in the host plants under continuous far-red light. However, the fern phytochrome did not interfere with the red-light repression of hypocotyl growth mediated by endogenous phytochrome B, and it failed to complement a phyB mutant phenotype. These observations suggest that the phy1 phytochrome molecule is too diverged from those of Arabidopsis to be fully functional.

Arabidopsis↗
PubMed1996

Action spectra for phytochrome A- and B-specific photoinduction of seed germination in Arabidopsis thaliana.

We have examined the seed germination in Arabidopsis thaliana of wild type (wt), and phytochrome A (PhyA)- and B (PhyB)-mutants in terms of incubation time and environmental light effects. Seed germination of the wt and PhyA-null mutant (phyA) was photoreversibly regulated by red and far-red lights of 10-1,000 micromol m-2 when incubated in darkness for 1-14 hr, but no germination occurred in PhyB-null mutant (phyB). When wt seeds and the phyB mutant seeds were incubated in darkness for 48 hr, they synthesized PhyA during dark incubation and germinated upon exposure to red light of 1-100 nmol m-2 and far-red light of 0.5-10 micromol m-2, whereas the phyA mutant showed no such response. The results indicate that the seed germination is regulated by PhyA and PhyB but not by other phytochromes, and the effects of PhyA and PhyB are separable in this assay. We determined action spectra separately for PhyA- and PhyB-specific induction of seed germination at Okazaki large spectrograph. Action spectra for the PhyA response show that monochromatic 300-780 nm lights of very low fluence induced the germination, and this induction was not photoreversible in the range examined. Action spectra for the PhyB response show that germination was photoreversibly regulated by alternate irradiations with light of 0.01-1 mmol m-2 at wavelengths of 540-690 nm and 695-780 nm. The present work clearly demonstrated that PhyA photoirreversibly triggers the germination upon irradiations with ultraviolet, visible and far-red light of very low fluence, while PhyB controls the photoreversible effects of low fluence.

Antibodies, Monoclonal↗
PubMed1996

Over-expression of a C-terminal region of phytochrome B.

In an attempt to identify domains directly involved in the signal transduction of phytochrome B (phyB), we over-expressed the achromophoric C-terminal half of phyB under control of the CaMV-35S promoter in transgenic Arabidopsis. In three independent transgenic lines, we detected accumulation of the introduced protein of predicted size at levels higher than that of the endogenous phyB by immunoblot analysis. Although these transgenic plants did not show any phenotype in the dark, enhancement of the phyB-dependent inhibition of hypocotyl elongation and reduction of the phytochrome A (phyA)-dependent inhibition were observed.

Arabidopsis↗
PubMed1996

Nuclear localization activity of phytochrome B.

Phytochromes are soluble red/far-red-light photoreceptor proteins which mediate various photomorphogenic responses of plants. Despite much effort, the signal transduction mechanism of phytochrome has remained obscure. Phytochromes are encoded by a small multigene family in Arabidopsis. Among the members of the family, phytochrome A (phyA) and B (phyB) are the best characterized. PhyB contains putative nuclear localization signals within its C-terminal region. Transgenic Arabidopsis plants were produced with expressed a fusion protein consisting of GUS and C-terminal fragments of phyB. GUS staining from the fusion protein in these transgenic plants was observed in the nucleus, which suggests that the nuclear localization signal of the fragment is functional. Next, it was examined whether the endogenous phyB was detected in the nucleus. Nuclei were isolated from the light-grown wild-type Arabidopsis leaves and subjected to the immunoblot analysis. The result indicated that a substantial fraction of total phyB was recovered in the isolated nuclei. This result was further confirmed by the immunocytochemical analysis of the protoplasts. Finally, the effects of light treatments on the levels of phyB in the isolated nuclei were examined. Dark adaptation of the plants before the nuclear isolation reduced the levels of phyB. The reduction was accelerated by irradiation of plants with far-red light before the transfer to darkness. Thus, nuclear localization of phyB was suggested to be light-dependent.

Arabidopsis↗
PubMed1995

Far-red light-insensitive, phytochrome A-deficient mutants of tomato.

We have selected two recessive mutants of tomato with slightly longer hypocotyls than the wild type, one under low fluence rate (3 mumol/m2/s) red light (R) and the other under low fluence rate blue light. These two mutants were shown to be allelic and further analysis revealed that hypocotyl growth was totally insensitive to far-red light (FR). We propose the gene symbol fri (far-red light insensitive) for this locus and have mapped it on chromosome 10. Immunochemically detectable phytochrome A polypeptide is essentially absent in the fri mutants as is the bulk spectrophotometrically detectable labile phytochrome pool in etiolated seedlings. A phytochrome B-like polypeptide is present in normal amounts and a small stable phytochrome pool can be readily detected by spectrophotometry in the fri mutants. Inhibition of hypocotyl growth by a R pulse given every 4 h is quantitatively similar in the fri mutants and wild type and the effect is to a large extent reversible if R pulses are followed immediately by a FR pulse. After 7 days in darkness, both fri mutants and the wild type become green on transfer to white light, but after 7 days in FR, the wild-type seedlings that have expanded their cotyledons lose their capacity to green in white light, while the fri mutants de-etiolate. Adult plants of the fri mutants show retarded growth and are prone to wilting, but exhibit a normal elongation response to FR given at the end of the daily photoperiod. The inhibition of seed germination by continuous FR exhibited by the wild type is normal in the fri mutants.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosome Mapping↗
PubMed1995

Effects of gibberellins on seed germination of phytochrome-deficient mutants of Arabidopsis thaliana.

Experiments were carried out to explore the involvement of gibberellins (GAs) in the light-induced germination of Arabidopsis thaliana (L.) Heynh, using wild type (WT) and phytochrome-deficient mutants (phyA, phyB and phyAphyB deficient in phytochrome A, B and A plus B, respectively). Seed germination of WT and phytochrome-deficient mutants was inhibited by uniconazole (an inhibitor of an early step in biosynthesis of GA, the oxidation of ent-kaurene) and prohexadione (an inhibitor of late steps, namely, 2 beta- and 3 beta-hydroxylation). This inhibition was overcome by simultaneous application of 10(-5) M GA4. The relative activity of GAs for promoting germination of uniconazole-treated seeds was GA4 > GA1 = GA9 > GA20. The wild type and the phyA and phyB mutants had an increased response to a red light pulse in the presence of GA1, GA4, GA9, GA20 and GA24 but there were no significant differences in activity of each GA between the mutants. Therefore, neither phytochrome A nor hytochrome B appears to regulate GA biosynthesis from GA12 to GA4 during seed germination, since the conversion of GA12 to GA9 is regulated by one enzyme (GA 20-oxidase). However, GA responsiveness appears to be regulated by phytochromes other than phytochromes A and B, since the phyAphyB double mutant retains the photoreversible increased response to GAs after a red light pulse.

Arabidopsis↗
PubMed1993

Identification of photo-inactive phytochrome A in etiolated seedlings and photo-active phytochrome B in green leaves of the aurea mutant of tomato.

The contents of spectrophotometrically measurable phytochrome A (PhyA) and phytochrome B (PhyB) and the corresponding immunochemically detectable apoproteins (PHYA and PHYB) were examined in dark- and light-grown tissues of the aurea mutant of tomato and its wild-type (WT). The amount of PHYA in etiolated aurea seedlings was found to be about 20% of that in the WT; this PHYA showed no photo-reversible changes in absorbance, no downregulation of the level of PHYA in light-grown seedlings, and no differential proteolysis of Pr and Pfr species in vitro which was seen in the case of the WT. By contrast, the amount of PHYB in aurea seedlings was not significantly different from that in WT seedlings. Phytochrome isolated from green leaves of the aurea mutant and purified by ion-exchange chromatography showed a red/far-red reversible spectral change, and its elution profile during chromatography was essentially similar to that of PHYB. The results indicate that aurea is a mutant that is deficient in photoactive PhyA at the etiolated stage, when it contains a spectrally inactive PHYA. However, the mutant contains spectrally active PhyB in its green tissue as does the WT.

Enzyme Activation↗