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Masahiro Kasahara

Publications and source records attributed to Masahiro Kasahara.

10 recordsLinked to original sources
PubMed2005

UV-A induces two calcium waves in Physcomitrella patens.

Our understanding of the role of Ca2+ in blue/UV-A photoreceptor signaling in a single cell is limited. Insight into calcium signaling has now been attained in Physcomitrella patens and its cryptochrome and phototropin knock-outs. Physcomitrella patens caulonemal filaments grow in the dark by apical extension and their apical cells are highly polarized. Fura-2-dextran ratio images of the apical cell from wild type (WT), Ppcry1a/1b and PpphotA2/B1/B2 were obtained immediately following UV-A exposure (30 microW cm(-2) at 340 nm for 1,000 ms plus 30 microW cm(-2) at 380 nm for 1,000 ms) [abbreviated as 1,000 ms (340/380 nm)] and demonstrated two intracellular waves: a Ca2+ wave from the growing apical tip through the apical cap, and a wave from the junction of the neighboring cell through the vacuolar, nuclear and plastid regions. In WT, the UV-A-induced tip wave increase had a magnitude of 454.0 +/- 40 nM, traveled at a rate of 3.4 +/- 0.7 microm s(-1) and was complete within 26.6 +/- 2.3 s, while the basal vacuolar wave had a magnitude of 596.8 +/- 110 nM, a rate of 8.4 +/- 0.8 microm s(-1) and duration of 25.3 +/- 4.9 s. Subsequent Ca2+ spikes of similar magnitude followed these waves. The amplitude of the Ca2+ waves in the apical cap and basal vacuolar regions of Ppcry1a/1b were higher than those in the WT, while the duration of those in PpphotA2/B1/B2 was longer. Subsequent Ca2+ spikes occurred in WT and Ppcry1a/1b but not in PpphotA2/B1/B2. When Mn2+ was added to the culture medium, the [Ca2+](cyt) increase was delayed, did not move as a wave and lasted longer. The results indicate that plants respond to blue light and UV-A radiation by generating a wave of changes in the [Ca2+](cyt). The characteristics of these Ca2+ waves were dependent upon cryptochrome and phototropin. Blue/UV-A signaling in P. patens appears to differ from that in Arabidopsis.

Bryopsida↗
PubMed2004

Phototropins mediate blue and red light-induced chloroplast movements in Physcomitrella patens.

Phototropin is the blue-light receptor that mediates phototropism, chloroplast movement, and stomatal opening in Arabidopsis. Blue and red light induce chloroplast movement in the moss Physcomitrella patens. To study the photoreceptors for chloroplast movement in P. patens, four phototropin genes (PHOTA1, PHOTA2, PHOTB1, and PHOTB2) were isolated by screening cDNA libraries. These genes were classified into two groups (PHOTA and PHOTB) on the basis of their deduced amino acid sequences. Then phototropin disruptants were generated by homologous recombination and used for analysis of chloroplast movement. Data revealed that blue light-induced chloroplast movement was mediated by phototropins in P. patens. Both photA and photB groups were able to mediate chloroplast avoidance, as has been reported for Arabidopsis phot2, although the photA group contributed more to the response. Red light-induced chloroplast movement was also significantly reduced in photA2photB1photB2 triple disruptants. Because the primary photoreceptor for red light-induced chloroplast movement in P. patens is phytochrome, phototropins may be downstream components of phytochromes in the signaling pathway. To our knowledge, this work is the first to show a function for the phototropin blue-light receptor in a response to wavelengths that it does not absorb.

Base Sequence↗
PubMed2004

Interaction of tomato mosaic virus movement protein with tobacco RIO kinase.

Tomato mosaic virus (ToMV) has a regulatory gene encoding a movement protein (MP) that is involved in the cell-to-cell movement of viral RNA through plasmodesmata. To identify the host cell factors interacting with ToMV MP, we used a recombinant MP probe to isolate cDNA clones from a phage expression library of Nicotiana tabacum by a far-Western screening method. One of the cDNA clones encoded an MP-interacting protein, MIP-T7, homologous to the yeast novel protein kinase, Rio1p. We isolated a full-length cDNA by RT-PCR. The putative gene product was designated NtRIO, and shared 33 and 73% amino acid identity with yeast and Arabidopsis RIO kinases, respectively. In vitro analyses using recombinant proteins showed that NtRIO also interacted with a different MP derived from Cucumber mosaic virus. NtRIO had autophosphorylation activity and phosphorylated ToMV MP. Addition of recombinant tobacco casein kinase 2 resulted in a marked increase in the phosphorylation of NtRIO. The interaction between NtRIO and ToMV MP was inhibited by phosphorylation of NtRIO.

Amino Acid Sequence↗
PubMed2004

The genome sequence of silkworm, Bombyx mori.

We performed threefold shotgun sequencing of the silkworm (Bombyx mori) genome to obtain a draft sequence and establish a basic resource for comprehensive genome analysis. By using the newly developed RAMEN assembler, the sequence data derived from whole-genome shotgun (WGS) sequencing were assembled into 49,345 scaffolds that span a total length of 514 Mb including gaps and 387 Mb without gaps. Because the genome size of the silkworm is estimated to be 530 Mb, almost 97% of the genome has been organized in scaffolds, of which 75% has been sequenced. By carrying out a BLAST search for 50 characteristic Bombyx genes and 11,202 non-redundant expressed sequence tags (ESTs) in a Bombyx EST database against the WGS sequence data, we evaluated the validity of the sequence for elucidating the majority of silkworm genes. Analysis of the WGS data revealed that the silkworm genome contains many repetitive sequences with an average length of <500 bp. These repetitive sequences appear to have been derived from truncated transposons, which are interspersed at 2.5- to 3-kb intervals throughout the genome. This pattern suggests that silkworm may have an active mechanism that promotes removal of transposons from the genome. We also found evidence for insertions of mitochondrial DNA fragments at 9 sites. A search for Bombyx orthologs to Drosophila genes controlling sex determination in the WGS data revealed 11 Bombyx genes and suggested that the sex-determining systems differ profoundly between the two species.

Animals↗
PubMed2004

Function analysis of phototropin2 using fern mutants deficient in blue light-induced chloroplast avoidance movement.

Gametophytes of the fern Adiantum capillus-veneris L. were mutagenized by heavy ion beam irradiation and screened for mutants lacking chloroplast avoidance movement under high intensity blue light. Mutants recovered include several with small deletions in the AcPHOT2 gene. The avoidance movement response in these mutants could be restored by transient expression of non-mutant AcPHOT2 cDNA, indicating that the chloroplast avoidance movement in this fern is mediated by the Acphot2 protein. Further functional analyses of the Acphot2 protein were performed using this transient assay for chloroplast avoidance movement. The results obtained suggest that the LOV2, but not the LOV1, domain of Acphot2 is essential for avoidance movement, and that several residues in the C-terminus of the kinase domain contribute to the avoidance response. The rate of dark reversion of the photo-activated LOV2 domain, which was calculated photometrically, was too fast to account for the lifetime of phot2 signal estimated from physiological responses. However, the rate of dark reversion of the combined domains of LOV1 and LOV2 did correspond to the lifetime of the signal, suggesting that LOV1 might have some function in this response, although it is not essential for playing a role as a photoreceptor.

Adiantum↗
PubMed2003

Chloroplast unusual positioning1 is essential for proper chloroplast positioning.

The intracellular distribution of organelles is a crucial aspect of effective cell function. Chloroplasts change their intracellular positions to optimize photosynthetic activity in response to ambient light conditions. Through screening of mutants of Arabidopsis defective in chloroplast photorelocation movement, we isolated six mutant clones in which chloroplasts gathered at the bottom of the cells and did not distribute throughout cells. These mutants, termed chloroplast unusual positioning (chup), were shown to belong to a single genetic locus by complementation tests. Observation of the positioning of other organelles, such as mitochondria, peroxisomes, and nuclei, revealed that chloroplast positioning and movement are impaired specifically in this mutant, although peroxisomes are distributed along with chloroplasts. The CHUP1 gene encodes a novel protein containing multiple domains, including a coiled-coil domain, an actin binding domain, a Pro-rich region, and two Leu zipper domains. The N-terminal hydrophobic segment of CHUP1 was expressed transiently in leaf cells of Arabidopsis as a fusion protein with the green fluorescent protein. The fusion protein was targeted to envelope membranes of chloroplasts in mesophyll cells, suggesting that CHUP1 may localize in chloroplasts. A glutathione S-transferase fusion protein containing the actin binding domain of CHUP1 was found to bind F-actin in vitro. CHUP1 is a unique gene identified that encodes a protein required for organellar positioning and movement in plant cells.

Amino Acid Sequence↗
PubMed2002

Photochemical properties of the flavin mononucleotide-binding domains of the phototropins from Arabidopsis, rice, and Chlamydomonas reinhardtii.

Phototropins (phot1 and phot2, formerly designated nph1 and npl1) are blue-light receptors that mediate phototropism, blue light-induced chloroplast relocation, and blue light-induced stomatal opening in Arabidopsis. Phototropins contain two light, oxygen, or voltage (LOV) domains at their N termini (LOV1 and LOV2), each a binding site for the chromophore flavin mononucleotide (FMN). Their C termini contain a serine/threonine protein kinase domain. Here, we examine the kinetic properties of the LOV domains of Arabidopsis phot1 and phot2, rice (Oryza sativa) phot1 and phot2, and Chlamydomonas reinhardtii phot. When expressed in Escherichia coli, purified LOV domains from all phototropins examined bind FMN tightly and undergo a self-contained photocycle, characterized by fluorescence and absorption changes induced by blue light (T. Sakai, T. Kagawa, M. Kasahara, T.E. Swartz, J.M. Christie, W.R. Briggs, M. Wada, K. Okada [2001] Proc Natl Acad Sci USA 98: 6969-6974; M. Salomon, J.M. Christie, E. Knieb, U. Lempert, W.R. Briggs [2000] Biochemistry 39: 9401-9410). The photocycle involves the light-induced formation of a cysteinyl adduct to the C(4a) carbon of the FMN chromophore, which subsequently breaks down in darkness. In each case, the relative quantum efficiencies for the photoreaction and the rate constants for dark recovery of LOV1, LOV2, and peptides containing both LOV domains are presented. Moreover, the data obtained from full-length Arabidopsis phot1 and phot2 expressed in insect cells closely resemble those obtained for the tandem LOV-domain fusion proteins expressed in E. coli. For both Arabidopsis and rice phototropins, the LOV domains of phot1 differ from those of phot2 in their reaction kinetic properties and relative quantum efficiencies. Thus, in addition to differing in amino acid sequence, the phototropins can be distinguished on the basis of the photochemical cycles of their LOV domains. The LOV domains of C. reinhardtii phot also undergo light-activated spectral changes consistent with cysteinyl adduct formation. Thus, the phototropin family extends over a wide evolutionary range from unicellular algae to higher plants.

Animals↗
PubMedDate not supplied

Chloroplast avoidance movement reduces photodamage in plants.

When plants are exposed to light levels higher than those required for photosynthesis, reactive oxygen species are generated in the chloroplasts and cause photodamage. This can occur even under natural growth conditions. To mitigate photodamage, plants have developed several protective mechanisms. One is chloroplast avoidance movement, in which chloroplasts move from the cell surface to the side walls of cells under high light conditions, although experimental support is still awaited. Here, using different classes of mutant defective in chloroplast avoidance movement, we show that these mutants are more susceptible to damage in high light than wild-type plants. Damage of the photosynthetic apparatus and subsequent bleaching of leaf colour and necrosis occur faster under high light conditions in the mutants than in wild-type plants. We conclude that chloroplast avoidance movement actually decreases the amount of light absorption by chloroplasts, and might therefore be important to the survival of plants under natural growth conditions.

Antioxidants↗
PubMedDate not supplied

A phytochrome-like protein AphC triggers the cAMP signaling induced by far-red light in the cyanobacterium Anabaena sp. strain PCC7120.

In the filamentous, nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, red light (630 nm) decreased, whereas far-red light (720 nm) increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content. To find a red and far-red light photoreceptor that triggers the cAMP signal cascade, we disrupted 10 open reading frame having putative chromophore-binding GAF domains. The response of the cellular cAMP concentration to red and far-red light in each open reading frame disruptant was determined. It was found that only the mutant of the gene all2699 failed to respond to far-red light. The open reading frame named as aphC encoded a protein with 920 amino acids including GAF domains similar to those involved in Cph2, a photoreceptor of Synechocystis sp. PCC6803. To determine which adenylate cyclase (AC) is responsible for far-red light signal, we disrupted all AC genes and found that CyaC was the candidate. The enzymatic activity of CyaC might be controlled by a far-red light photoreceptor through the phosphotransfer reaction. The site-specific mutant of the Asp59 residue of the receiver (R1) domain of CyaC lost its light-response capability. It was suggested that the far-red light signal was received by AphC and then transferred to the N-terminal response regulator domain of CyaC. Then its catalytic activity was stimulated, which increased the cellular cAMP concentration and drove the subsequent signal transduction cascade.

Adenylyl Cyclases↗