Papers by Masanori Tamaoki
Ozone is the main photochemical oxidant that causes leaf damage in many plant species, thereby de... more Ozone is the main photochemical oxidant that causes leaf damage in many plant species, thereby decreasing the productivity of crops and forests. Ozone produces reactive oxygen species suchas superoxide radicals and hydrogen peroxide, which induce phytohormones such as ethylene, salicylic acid and jasmonic acid. Phytohormones are required for plant growth, development and defense response. It is also known that phytohormones regulate the extent of leaf injury in ozone-fumigated plants. In recent years, responses to ozone have been studied using genetic-modified plants and mutants, which have aitered the hormone levels and signaling. From this researches, the role of phytohormones and the complexity of their signaling is being clarified. The present focused on the biosynthesis of phytohormones and their cross-talking effects in ozone-exposed plants.
Plant and Cell Physiology, 1995
Plant and Cell Physiology, 1997
Plant and Cell Physiology, 2005
To clarify the processes involved in plant immunity, we have isolated and characterized a single ... more To clarify the processes involved in plant immunity, we have isolated and characterized a single recessive Arabidopsis mutant, cad1 (constitutively activated cell death 1), which shows a phenotype that mimics the lesions seen in the hypersensitive response (HR). This mutant shows spontaneously activated expression of pathogenesis-related (PR) genes, and leading to a 32-fold increase in salicylic acid (SA). Inoculation of cad1 mutant plants with Pseudomonas syringae pv tomato DC3000 shows that the cad1 mutation results in the restriction of bacterial growth. Cloning of CAD1 reveals that this gene encodes a protein containing a domain with significant homology to the MACPF (membrane attack complex and perforin) domain of complement components and perforin proteins that are involved in innate immunity in animals. Furthermore, cell death is suppressed in transgenic cad1 plants expressing nahG, which encodes an SA-degrading enzyme. We therefore conclude that the CAD1 protein negatively controls the SA-mediated pathway of programmed cell death in plant immunity.
Plant and Cell Physiology, 2008
To understand better the plant response to ozone, we isolated and characterized an ozone-sensitiv... more To understand better the plant response to ozone, we isolated and characterized an ozone-sensitive (ozs1) mutant strain from a set of T-DNA-tagged Arabidopsis thaliana ecotype Columbia. The mutant plants show enhanced sensitivity to ozone, desiccation and sulfur dioxide, but have normal sensitivity to hydrogen peroxide, low temperature and high light levels. The T-DNA was inserted at a single locus which is linked to ozone sensitivity. Identification of the genomic sequences flanking the T-DNA insertion revealed disruption of a gene encoding a transporter-like protein of the tellurite resistance/C 4-dicarboxylate transporter family. Plants with either of two different T-DNA insertions in this gene were also sensitive to ozone, and these plants failed to complement ozs1. Transpiration levels, stomatal conductance levels and the size of stomatal apertures were greater in ozs1 mutant plants than in the wild type. The stomatal apertures of ozs1 mutant plants responded to light fluctuations but were always larger than those of the wild-type plants under the same conditions. The stomata of the mutant and wild-type plants responded similarly to stimuli such as light, abscisic acid, high concentrations of carbon dioxide and ozone. These results suggest that OZS1 helps to close stomata, being not involved in the responses to these signals.
Plant and Cell Physiology, 1998
Pea mutant E135 (syml3) forms ineffective (Fix") nodules that lack nitrogen fixing activity. To d... more Pea mutant E135 (syml3) forms ineffective (Fix") nodules that lack nitrogen fixing activity. To determine the developmental step blocked in E135 nodules we studied the nitrogenase activities in isolated bacteroids and in cell-free extracts of bacteroids, and measured the two components of nitrogenase protein in bacteroids. Bacteroids prepared anaerobically from E135 nodules showed no acetylene reduction activity in the presence and absence of myoglobin. Furthermore, no acetylene reduction activity by cell-free extracts of E135 bacteroids was detected in the presence of ATP-generating system and dithionite. However, immunoblotting analyses revealed the presence of nitrogenase components I and II in E135 nodule bacteroids. These results suggest that a host plant gene is involved in the expression of nitrogenase activity in symbiotic bacteria.
Plant and Cell Physiology, 1997
The shoot apical meristem functions to generate the lateral organs of a plant throughout the vege... more The shoot apical meristem functions to generate the lateral organs of a plant throughout the vegetative and reproductive phases. Homeobox genes play key roles in controlling such developmental programs, but their modes of action have not been well defined. Here we describe isolation and biological functions of a novel tobacco homeobox gene, designated NTH1S (Nicotiana tabacum homeobox 15), from a tobacco shoot apex cDNA library. NTH15 encodes a polypeptide of 342 amino acids, its homeodomain is very similar to the class 1 KNOTTED-type homeodomains. NTH1S mRNA is mainly localized in corpus cells in the tobacco shoot apical meristem, but not in tunica layers nor in differentiated lateral organs. The NTH15 cDNA was fused to the cauliflower mosaic virus 35S promoter and used to generate transgenic tobacco plants. Almost all transgenic tobacco plants showed abnormal leaf and/or flower morphology, and were categorized into three groups depending on severity of the leaf phenotype. In transgenic leaves, drastic decrease of GA, and increase of cytokinin were observed, while the levels of other phytohormones were only slightly changed. Taken together, our results suggest NTH15 is involved in tobacco morphogenesis and abnormal leaf morphology in transgenic plants results from altered hormone levels.
Plant and Cell Physiology, 2012
Legume plants establish a symbiotic association with bacteria called rhizobia, resulting in the f... more Legume plants establish a symbiotic association with bacteria called rhizobia, resulting in the formation of nitrogen-fixing root nodules. A Lotus japonicus symbiotic mutant, sen1, forms nodules that are infected by rhizobia but that do not fix nitrogen. Here, we report molecular identification of the causal gene, SEN1, by map-based cloning. The SEN1 gene encodes an integral membrane protein homologous to Glycine max nodulin-21, and also to CCC1, a vacuolar iron/manganese transporter of Saccharomyces cerevisiae, and VIT1, a vacuolar iron transporter of Arabidopsis thaliana. Expression of the SEN1 gene was detected exclusively in nodule-infected cells and increased during nodule development. Nif gene expression as well as the presence of nitrogenase proteins was detected in rhizobia from sen1 nodules, although the levels of expression were low compared with those from wild-type nodules. Microscopic observations revealed that symbiosome and/or bacteroid differentiation are impaired in the sen1 nodules even at a very early stage of nodule development. Phylogenetic analysis indicated that SEN1 belongs to a protein clade specific to legumes. These results indicate that SEN1 is essential for nitrogen fixation activity and symbiosome/bacteroid differentiation in legume nodules.
Plant and Cell Physiology, 2005
Dehydroascorbate reductase (DHAR) is a key component of the ascorbate recycling system. Three fun... more Dehydroascorbate reductase (DHAR) is a key component of the ascorbate recycling system. Three functional DHAR genes are encoded in the Arabidopsis genome. Ozone exposure increased the expression of the cytosolic DHAR (cytDHAR) gene alone. We characterized an Arabidopsis mutant with a deficient cytDHAR. The mutant completely lacked cytDHAR activity and was highly ozone sensitive. The amounts of total ascorbate and glutathione were similar in both lines, but the amount of apoplastic ascorbate in the mutant was 61.5% lower. These results indicate that the apoplastic ascorbate, which is generated through the reduction of DHA by cytDHAR, is important for ozone tolerance.
Plant and Cell Physiology, 2000
We compared the phenotypes of transgenic tobacco plants over-expressing various knottedl-type cla... more We compared the phenotypes of transgenic tobacco plants over-expressing various knottedl-type classl homeobox genes. All transformants showed abnormal leaf morphology, with the degree of abnormality depending upon the Nicotiana tabacum homeobox (NTH) gene that was over-expressed. Tobacco plants over-expressing NTH1 or NTH9 showed a relatively weak phenotype, while NTH15 and NTH20 over-expressing plants exhibited severe alterations, with occasional ectopic shoot formation on the leaves. Plants over-expressing NTH22 had a relatively severe phenotype, but did not form any ectopic shoots. These results indicate that all of the NTH genes can influence leaf development from the shoot apical meristem, but that the effect varies with the gene. Based on phylogenetic analysis of the NTH genes and comparison of the phenotypes of plants over-expressing them, we suggest that the Ay*/-type classl family can be divided into two subgroups, and that the differences in their ability to induce the abnormal phenotype corresponds to the structures of their conserved domains.
Physiologia Plantarum, 2009
Ozone produces reactive oxygen species and induces the synthesis of phytohormones, including ethy... more Ozone produces reactive oxygen species and induces the synthesis of phytohormones, including ethylene and salicylic acid. These phytohormones act as signal molecules that enhance cell death in response to ozone exposure. However, some studies have shown that ethylene and salicylic acid can instead decrease the magnitude of ozone-induced cell death. Therefore, we studied the defensive roles of ethylene and salicylic acid against ozone. Unlike the wild-type, Col-0, Arabidopsis mutants deficient in ethylene signaling (ein2) or salicylic acid biosynthesis (sid2) generated high levels of superoxide and exhibited visible leaf injury, indicating that ethylene and salicylic acid can reduce ozone damage. Macroarray analysis suggested that the ethylene and salicylic acid defects influenced glutathione (GSH) metabolism. Increases in the reduced form of GSH occurred in Col-0 6 h after ozone exposure, but little GSH was detected in ein2 and sid2 mutants, suggesting that GSH levels were affected by ethylene or salicylic acid signaling. We performed gene expression analysis by real-time polymerase chain reaction using genes involved in GSH metabolism. Induction of γ-glutamylcysteine synthetase (GSH1), glutathione synthetase (GSH2), and glutathione reductase 1 (GR1) expression occurred normally in Col-0, but at much lower levels in ein2 and sid2. Enzymatic activities of GSH1 and GSH2 in ein2 and sid2 were significantly lower than in Col-0. Moreover, ozone-induced leaf damage observed in ein2 and sid2 was mitigated by artificial elevation of GSH content. Our results suggest that ethylene and salicylic acid protect against ozone-induced leaf injury by increasing de novo biosynthesis of GSH.
OMICS: A Journal of Integrative Biology, 2003
Light-dependent transcriptional activation of the photolyase gene imparts UVB tolerance to a plan... more Light-dependent transcriptional activation of the photolyase gene imparts UVB tolerance to a plant. In the present study, the cucumber CPD photolyase gene (CsPHR) was isolated from a genomic DNA library and its genomic structure was scrutinized. As a result, putative light-responsive cis-acting elements were found in the CsPHR promoter.
Molecular Genetics and Genomics, 2008
Arabidopsis SUPERMAN (SUP) and members of its family are plant-unique C 2 H 2-type zinc Wnger gen... more Arabidopsis SUPERMAN (SUP) and members of its family are plant-unique C 2 H 2-type zinc Wnger genes that have been implicated in plant growth and development. In this paper, we report that a new SUP-family gene, designated as SA-and ABA-downregulated zinc Wnger gene (SAZ), is involved in the negative regulation of ABA-mediated signaling. SAZ-GUS fusion proteins were predominantly localized in the nuclei when they were transiently expressed in onion epidermal cells. SAZ transcripts were expressed in the leaves and pistils of very young Xower buds. In young seedlings, SAZ expression was downregulated in response to environmental stresses such as drought, salt, ozone and ultraviolet-B irradiation. This downregulation was also observed in response to the phytohormones salicylic acid (SA) and abscisic acid (ABA). SA-responsive downregulation of SAZ was not observed in the npr1-1 mutant, indicating that this regulation is NPR1 dependent. RNAi-mediated knockdown of SAZ (SAZ-kd) resulted in elevated expression of the drought-and ABA-responsive genes rd29B and rab18 under unstressed conditions, and it enhanced the response of these genes to drought and ABA treatment. The expression of several other drought-and/or ABA-responsive genes was not aVected by SAZ-kd. Based on these results, we propose that SAZ plays a role in repressing a subset of the ABA-mediated stress-responsive genes in unstressed conditions.
MGG Molecular & General Genetics, 1996
Transgenic tobacco plants were generated carrying a rice homeobox gene, OSH1, controlled by the p... more Transgenic tobacco plants were generated carrying a rice homeobox gene, OSH1, controlled by the promoter of a gene encoding a tobacco pathogenesis-related protein (PR1a). These lines were morphologically abnormal, with wrinkled and/or lobed leaves. Histological analysis of shoot apex primordia indicates arrest of lateral leaf blade expansion, often resulting in asymmetric and anisotrophic growth of leaf blades. Other notable abnormalities included abnormal or arrested development of leaf lateral veins. Interestingly, OHS1 expression was undetectable in mature leaves with the aberrant morphological features. Thus, OSH1 expression in mature leaves is not necessary for abnormal leaf development. Northern blot and in situ hybridization analyses indicate that PR1a-OSH1 is expressed only in the shoot apical meristem and in very young leaf primordia. Therefore, the aberrant morphological features are an indirect consequence of ectopic OSH1 gene expression. The only abnormality observed in tissues expressing the transgene was periclinal (rather than anticlinal) division in mesophyll cells during leaf blade initiation. This generates thicker leaf blades and disrupts the mesophyll cell layers, from which vascular tissues differentiate. The OSH1 product appears to affect the mechanism controlling the orientation of the plane of cell division, resulting in abnormal periclinal division of mesophyll cell, which in turn results in the gross morphological abnormalities observed in the transgenic lines.
Journal of Plant Research, 2011
Myo-inositol monophosphatase (IMP) catalyzes the dephosphorylation of myo-inositol 3-phosphate in... more Myo-inositol monophosphatase (IMP) catalyzes the dephosphorylation of myo-inositol 3-phosphate in the last step of myo-inositol biosynthesis. IMP is also important in phosphate metabolism and is required for the biosynthesis of cell wall polysaccharides, phytic acid, and phosphatidylinositol. In Arabidopsis, IMP is encoded by VTC4. There are, however, two additional IMP candidate genes, IMPL1 and IMPL2, which have not yet been elucidated. In our genetic studies of Arabidopsis IMP genes, only the loss-of-function mutant impl2 showed embryonic lethality at the globular stage. All IMP genes were expressed in a similar manner both in the vegetative and reproductive organs. In developing seeds, expression of IMP genes was not coupled with the expression of the genes encoding myo-inositol phosphate synthases (MIPSs), which supply the substrate for IMPs in the de novo synthesis pathway. Instead, expression of IMP genes was correlated with expression of the gene for myo-inositol polyphosphate 1-phosphatase (SAL1), which is involved in the myo-inositol salvage pathway, suggesting a possible salvage pathway role in seed development. Moreover, the partial rescue of the impl2 phenotype by histidine application implies that IMPL2 is also involved in histidine biosynthesis during embryo development.
Journal of Plant Research, 2009
Plants have evolved intricate mechanisms to respond and adapt to a wide variety of biotic and abi... more Plants have evolved intricate mechanisms to respond and adapt to a wide variety of biotic and abiotic stresses in their environment. The Arabidopsis DEAR1 (DREB and EAR motif protein 1; At3g50260) gene encodes a protein containing significant homology to the DREB1/CBF (dehydration-responsive element binding protein 1/C-repeat binding factor) domain and the EAR (ethylene response factor-associated amphiphilic repression) motif. We show here that DEAR1 mRNA accumulates in response to both pathogen infection and cold
Journal of Experimental Botany, 2006
Cytokinins and auxins are major phytohormones involved in various aspects of plant growth and dev... more Cytokinins and auxins are major phytohormones involved in various aspects of plant growth and development. These phytohormones are also known to antagonize the effects of abscisic acid (ABA) on stomatal movement, and to affect ethylene biosynthesis. As ethylene has an antagonistic effect on ABAinduced stomatal closure, the possibility that the antagonistic effects of these phytohormones on ABA were mediated through ethylene biosynthesis was investigated. Both the cytokinin, 6-benzyladenine (BA), and the auxin, 1-naphthaleneacetic acid (NAA), antagonized ABA-induced stomatal closure in a manner similar to that following application of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). However, these effects were negated when ethylene signalling, perception, or biosynthesis were blocked. As stomatal aperture is regulated by changes in guard cell volume, ABA application was found to reduce the volume of the guard cell protoplasts (GCP). It was found that BA, NAA, or ACC application compensated perfectly for the reduction in GCP volume by ABA application in WT plants. The above observations suggest that cytokinins and auxins inhibit ABA-induced stomatal closure through the modulation of ethylene biosynthesis, and that ethylene inhibits the ABAinduced reduction of osmotic pressure in the guard cells.
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Papers by Masanori Tamaoki