Tomohiko Kato

Publications of Tomohiko Kato

• Arabidopsis RPT2a encoding the 26S proteasome subunit is required for various aspects of root meristem maintenance, and regulates gametogenesis redundantly with its homolog, RPT2b.

  Authors: Minako Ueda, Keisuke Matsui, Sumie Ishiguro, Tomohiko Kato, Satoshi Tabata, Masatomo Kobayashi, Motoaki Seki, Kazuo Shinozaki, Kiyotaka Okada

  Plant & cell physiology. 07/2011; 52(9):1628-40.

  The 26S proteasome plays fundamental roles in the degradation of short-lived regulatory proteins, thereby controlling diverse cellular processes. In Arabidopsis, the essential RPT2 subunit is encodedThe 26S proteasome plays fundamental roles in the degradation of short-lived regulatory proteins, thereby controlling diverse cellular processes. In Arabidopsis, the essential RPT2 subunit is encoded by two highly homologous genes: RPT2a and RPT2b. Currently, only RPT2a has been reported to regulate various developmental processes, including the maintenance of the root apical meristem (RAM), although the roles of RPT2a in the RAM are still obscure. Here, we analyzed the cell type-specific requirement for RPT2a. When RPT2a was expressed locally in the rpt2a mutant, pleiotropic defects in the RAM, such as cell death and distorted cellular organization, were rescued differently, suggesting that RPT2a regulates various specific activities, which converge to maintain the RAM. On the other hand, the homologous RPT2b was also expressed in meristems, and the expression of RPT2b protein under the control of the RPT2a promoter complemented the rpt2a RAM defects, although the rpt2b mutant showed no obvious defect in all developmental aspects we examined. These results show that RPT2b might work in the RAM, but is dispensable for RAM maintenance in the presence of RPT2a. In contrast, the rpt2a rpt2b double mutant was lethal in male and female gametophytes, suggesting that RPT2a and RPT2b are redundantly required for gametogenesis. Furthermore, we showed that similar meristematic and gametophytic defects were caused by mutations in other subunit genes, RPT5a and RPT5b, suggesting that proper activity of the proteasome, not an RPT2-specific function, is required. Taken together, our results suggest that RPT2a and RPT2b contribute differently to the proteasome activity required for each developmental context.

• Comparative Genomics and Reverse Genetics Analysis Reveal Indispensable Functions of the Serine Acetyltransferase Gene Family in Arabidopsis.

  Authors: Mutsumi Watanabe, Keiichi Mochida, Tomohiko Kato, Satoshi Tabata, Naoko Yoshimoto, Masaaki Noji, Kazuki Saito

  The Plant cell. 10/2008;

  Ser acetyltransferase (SERAT), which catalyzes O-acetyl-Ser (OAS) formation, plays a key role in sulfur assimilation and Cys synthesis. Despite several studies on SERATs from various plant species,Ser acetyltransferase (SERAT), which catalyzes O-acetyl-Ser (OAS) formation, plays a key role in sulfur assimilation and Cys synthesis. Despite several studies on SERATs from various plant species, the in vivo function of multiple SERAT genes in plant cells remains unaddressed. Comparative genomics studies with the five genes of the SERAT gene family in Arabidopsis thaliana indicated that all three Arabidopsis SERAT subfamilies are conserved across five plant species with available genome sequences. Single and multiple knockout mutants of all Arabidopsis SERAT gene family members were analyzed. All five quadruple mutants with a single gene survived, with three mutants showing dwarfism. However, the quintuple mutant lacking all SERAT genes was embryo-lethal. Thus, all five isoforms show functional redundancy in vivo. The developmental and compartment-specific roles of each SERAT isoform were also demonstrated. Mitochondrial SERAT2;2 plays a predominant role in cellular OAS formation, while plastidic SERAT2;1 contributes less to OAS formation and subsequent Cys synthesis. Three cytosolic isoforms, SERAT1;1, SERAT3;1, and SERAT3;2, may play a major role during seed development. Thus, the evolutionally conserved SERAT gene family is essential in cellular processes, and the substrates and products of SERAT must be exchangeable between the cytosol and organelles.

• Genome Structure of the Legume, Lotus japonicus.

  Authors: Shusei Sato, Yasukazu Nakamura, Takakazu Kaneko, Erika Asamizu, Tomohiko Kato, Mitsuteru Nakao, Shigemi Sasamoto, Akiko Watanabe, Akiko Ono, Kumiko Kawashima [......] Chika Takahashi, Tsuyuko Wada, Manabu Yamada, Nobuko Ohmido, Makoto Hayashi, Kiichi Fukui, Tomoya Baba, Tomoko Nakamichi, Hirotada Mori, Satoshi Tabata

  DNA research : an international journal for rapid publication of reports on genes and genomes. 06/2008;

  The legume Lotus japonicus has been widely used as a model system to investigate the genetic background of legume-specific phenomena such as symbiotic nitrogen fixation. Here, we report structuralThe legume Lotus japonicus has been widely used as a model system to investigate the genetic background of legume-specific phenomena such as symbiotic nitrogen fixation. Here, we report structural features of the L. japonicus genome. The 315.1-Mb sequences determined in this and previous studies correspond to 67% of the genome (472 Mb), and are likely to cover 91.3% of the gene space. Linkage mapping anchored 130-Mb sequences onto the six linkage groups. A total of 10 951 complete and 19 848 partial structures of protein-encoding genes were assigned to the genome. Comparative analysis of these genes revealed the expansion of several functional domains and gene families that are characteristic of L. japonicus. Synteny analysis detected traces of whole-genome duplication and the presence of synteny blocks with other plant genomes to various degrees. This study provides the first opportunity to look into the complex and unique genetic system of legumes.

• The Arabidopsis OBERON1 and OBERON2 genes encode plant homeodomain finger proteins and are required for apical meristem maintenance.

  Authors: Shunsuke Saiga, Chihiro Furumizu, Ryusuke Yokoyama, Tetsuya Kurata, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Mitsuhiro Suzuki, Yoshibumi Komeda

  Development (Cambridge, England). 06/2008; 135(10):1751-9.

  Maintenance of the stem cell population located at the apical meristems is essential for repetitive organ initiation during the development of higher plants. Here, we have characterized the roles ofMaintenance of the stem cell population located at the apical meristems is essential for repetitive organ initiation during the development of higher plants. Here, we have characterized the roles of OBERON1 (OBE1) and its paralog OBERON2 (OBE2), which encode plant homeodomain finger proteins, in the maintenance and/or establishment of the meristems in Arabidopsis. Although the obe1 and obe2 single mutants were indistinguishable from wild-type plants, the obe1 obe2 double mutant displayed premature termination of the shoot meristem, suggesting that OBE1 and OBE2 function redundantly. Further analyses revealed that OBE1 and OBE2 allow the plant cells to acquire meristematic activity via the WUSCHEL-CLAVATA pathway, which is required for the maintenance of the stem cell population, and they function parallel to the SHOOT MERISTEMLESS gene, which is required for preventing cell differentiation in the shoot meristem. In addition, obe1 obe2 mutants failed to establish the root apical meristem, lacking both the initial cells and the quiescent center. In situ hybridization revealed that expression of PLETHORA and SCARECROW, which are required for stem cell specification and maintenance in the root meristem, was lost from obe1 obe2 mutant embryos. Taken together, these data suggest that the OBE1 and OBE2 genes are functionally redundant and crucial for the maintenance and/or establishment of both the shoot and root meristems.

• Ultrastructural characterization of exine development of the transient defective exine 1 mutant suggests the existence of a factor involved in constructing reticulate exine architecture from sporopollenin aggregates.

  Authors: Tohru Ariizumi, Takahiro Kawanabe, Katsunori Hatakeyama, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Kinya Toriyama

  Plant & cell physiology. 02/2008; 49(1):58-67.

  A male-sterile mutant of Arabidopsis thaliana, in which filament elongation was defective although pollen fertility was normal, was isolated by means of T-DNA tagging. Transmission electronA male-sterile mutant of Arabidopsis thaliana, in which filament elongation was defective although pollen fertility was normal, was isolated by means of T-DNA tagging. Transmission electron microscopy (TEM) analysis revealed that primexine synthesis and probacula formation, which are thought to be the initial steps of exine formation, were defective, and that globular sporopollenin aggregation was randomly deposited onto the microspore at the early uninucleate microspore stage. Sporopollenin aggregation, which failed to anchor to the microspore plasma membrane, was deposited on the locule wall and in the locule at the uninucleate microspore stage. However, visually normal exine with a basic reticulate structure was observed at the middle uninucleate microspore stage, indicating that the exine formation was restored in the mutant. Thus, the mutant was designated transient defective exine 1 (tde1). These results indicated that tde1 mutation affects the initial process of the exine formation, but does not impair any critical processes. Our results also suggest the existence of a certain factor responsible for exine patterning in A. thaliana. The TDE1 gene was found to be identical to the DE-ETIOLATED 2 gene known to be involved in brassinosteroid (BR) biosynthesis, and the tde1 probacula-defective phenotypes were recovered in the presence of BR application. These results suggest that BRs control the rate or efficiency of initial process of exine pattern formation.

• Arabidopsis TRANSPARENT TESTA GLABRA2 is directly regulated by R2R3 MYB transcription factors and is involved in regulation of GLABRA2 transcription in epidermal differentiation.

  Authors: Tetsuya Ishida, Sayoko Hattori, Ryosuke Sano, Kayoko Inoue, Yumiko Shirano, Hiroaki Hayashi, Daisuke Shibata, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Kiyotaka Okada, Takuji Wada

  The Plant cell. 09/2007; 19(8):2531-43.

  Arabidopsis thaliana TRANSPARENT TESTA GLABRA2 (TTG2) encodes a WRKY transcription factor and is expressed in young leaves, trichomes, seed coats, and root hairless cells. An examination of severalArabidopsis thaliana TRANSPARENT TESTA GLABRA2 (TTG2) encodes a WRKY transcription factor and is expressed in young leaves, trichomes, seed coats, and root hairless cells. An examination of several trichome and root hair mutants indicates that MYB and bHLH genes regulate TTG2 expression. Two MYB binding sites in the TTG2 5' regulatory region act as cis regulatory elements and as direct targets of R2R3 MYB transcription factors such as WEREWOLF, GLABRA1, and TRANSPARENT TESTA2. Mutations in TTG2 cause phenotypic defects in trichome development and seed color pigmentation. Transgenic plants expressing a chimeric repressor version of the TTG2 protein (TTG2:SRDX) showed defects in trichome formation, anthocyanin accumulation, seed color pigmentation, and differentiation of root hairless cells. GLABRA2 (GL2) expression was markedly reduced in roots of ProTTG2:TTG2:SRDX transgenic plants, suggesting that TTG2 is involved in the regulation of GL2 expression, although GL2 expression in the ttg2 mutant was similar to that in the wild type. Our analysis suggests a new step in a regulatory cascade of epidermal differentiation, in which complexes containing R2R3 MYB and bHLH transcription factors regulate the expression of TTG2, which then regulates GL2 expression with complexes containing R2R3 MYB and bHLH in the differentiation of trichomes and root hairless cells.

• Sugar-inducible expression of the nucleolin-1 gene of Arabidopsis thaliana and its role in ribosome synthesis, growth and development.

  Authors: Hisae Kojima, Takamasa Suzuki, Takenori Kato, Ken-ichi Enomoto, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Julio Sáez-Vasquez, Manuel Echeverría, Tsuyoshi Nakagawa, Sumie Ishiguro, Kenzo Nakamura

  The Plant journal : for cell and molecular biology. 04/2007; 49(6):1053-63.

  Animal and yeast nucleolin function as global regulators of ribosome synthesis, and their expression is tightly linked to cell proliferation. Although Arabidopsis contains two genes for nucleolin,Animal and yeast nucleolin function as global regulators of ribosome synthesis, and their expression is tightly linked to cell proliferation. Although Arabidopsis contains two genes for nucleolin, AtNuc-L1 is the predominant if not only form of the protein found in most tissues, and GFP-AtNuc-L1 fusion proteins were targeted to the nucleolus. Expression of AtNuc-L1 was strongly induced by sucrose or glucose but not by non-metabolizable mannitol or 2-deoxyglucose. Sucrose also caused enhanced expression of genes for subunits of C/D and H/ACA small nucleolar ribonucleoproteins, as well as a large number of genes for ribosomal proteins (RPs), suggesting that carbohydrate availability regulates de novo ribosome synthesis. In sugar-starved cells, induction of AtNuc-L1 occurred with 10 mM glucose, which seemed to be a prerequisite for resumption of growth. Disruption of AtNuc-L1 caused an increased steady-state level of pre-rRNA relative to mature 25S rRNA, and resulted in various phenotypes that overlap those reported for several RP gene mutants, including a reduced growth rate, prolonged lifetime, bushy growth, pointed leaf, and defective vascular patterns and pod development. These results suggest that the rate of ribosome synthesis in the meristem has a strong impact not only on the growth but also the structure of plants. The AtNuc-L1 disruptant exhibited significantly reduced sugar-induced expression of RP genes, suggesting that AtNuc-L1 is involved in the sugar-inducible expression of RP genes.

• Arabidopsis plasma membrane protein crucial for Ca2+ influx and touch sensing in roots.

  Authors: Yuko Nakagawa, Takeshi Katagiri, Kazuo Shinozaki, Zhi Qi, Hitoshi Tatsumi, Takuya Furuichi, Akio Kishigami, Masahiro Sokabe, Itaru Kojima, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Kazuko Iida, Asuka Terashima, Masataka Nakano, Mitsunobu Ikeda, Takuya Yamanaka, Hidetoshi Iida

  Proceedings of the National Academy of Sciences of the United States of America. 03/2007; 104(9):3639-44.

  Plants can sense and respond to mechanical stimuli, like animals. An early mechanism of mechanosensing and response is speculated to be governed by as-yet-unidentified sensory complexes containing aPlants can sense and respond to mechanical stimuli, like animals. An early mechanism of mechanosensing and response is speculated to be governed by as-yet-unidentified sensory complexes containing a Ca(2+)-permeable, stretch-activated (SA) channel. However, the components or regulators of such complexes are poorly understood at the molecular level in plants. Here, we report the molecular identification of a plasma membrane protein (designated Mca1) that correlates Ca(2+) influx with mechanosensing in Arabidopsis thaliana. MCA1 cDNA was cloned by the functional complementation of lethality of a yeast mid1 mutant lacking a putative Ca(2+)-permeable SA channel component. Mca1 was localized to the yeast plasma membrane as an integral membrane protein and mediated Ca(2+) influx. Mca1 also increased [Ca(2+)](cyt) upon plasma membrane distortion in Arabidopsis. The growth of MCA1-overexpressing plants was impaired in a high-calcium but not a low-calcium medium. The primary roots of mca1-null plants failed to penetrate a harder agar medium from a softer one. These observations demonstrate that Mca1 plays a crucial role in a Ca(2+)-permeable SA channel system that leads to mechanosensing in Arabidopsis. We anticipate our findings to be a starting point for a deeper understanding of the molecular mechanisms of mechanotransduction in plants.

• AHK5 histidine kinase regulates root elongation through an ETR1-dependent abscisic acid and ethylene signaling pathway in Arabidopsis thaliana.

  Authors: Ayako Iwama, Takafumi Yamashino, Yasushi Tanaka, Hitoshi Sakakibara, Tatsuo Kakimoto, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Akira Nagatani, Takeshi Mizuno

  Plant & cell physiology. 03/2007; 48(2):375-80.

  The Arabidopsis thaliana genome encodes a small family of histidine (His) protein kinases, some of which have redundant functions as ethylene receptors, whereas others serve as cytokinin receptors.The Arabidopsis thaliana genome encodes a small family of histidine (His) protein kinases, some of which have redundant functions as ethylene receptors, whereas others serve as cytokinin receptors. The most poorly characterized of these is authentic histidine kinase 5 (AHK5; also known as cytokinin-independent 2, CKI2). Here we characterize three independent ahk5 mutants, and show that they have a common phenotype. Our results suggest that AHK5 His-kinase acts as a negative regulator in the signaling pathway in which ethylene and ABA inhibit the root elongation through ETR1 (an ethylene receptor).

• Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis.

  Authors: Kaori Miyawaki, Petr Tarkowski, Miho Matsumoto-Kitano, Tomohiko Kato, Shusei Sato, Danuse Tarkowska, Satoshi Tabata, Göran Sandberg, Tatsuo Kakimoto

  Proceedings of the National Academy of Sciences of the United States of America. 11/2006; 103(44):16598-603.

  Cytokinins, which are central regulators of cell division and differentiation in plants, are adenine derivatives carrying an isopentenyl side chain that may be hydroxylated. Plants have two classesCytokinins, which are central regulators of cell division and differentiation in plants, are adenine derivatives carrying an isopentenyl side chain that may be hydroxylated. Plants have two classes of isopentenyltransferases (IPTs) acting on the adenine moiety: ATP/ADP isopentenyltransferases (in Arabidopsis thaliana, AtIPT1, 3, 4-8) and tRNA IPTs (in Arabidopsis, AtIPT2 and 9). ATP/ADP IPTs are likely to be responsible for the bulk of cytokinin synthesis, whereas it is thought that cis-zeatin (cZ)-type cytokinins are produced possibly by degradation of cis-hydroxy isopentenyl tRNAs, which are formed by tRNA IPTs. However, these routes are largely hypothetical because of lack of in vivo evidence, because the critical experiment necessary to verify these routes, namely the production and analysis of mutants lacking AtIPTs, has not yet been described. We isolated null mutants for all members of the ATP/ADP IPT and tRNA IPT gene families in Arabidopsis. Notably, our work demonstrates that the atipt1 3 5 7 quadruple mutant possesses severely decreased levels of isopentenyladenine and trans-zeatin (tZ), and their corresponding ribosides, ribotides, and glucosides, and is retarded in its growth. In contrast, these mutants possessed increased levels of cZ-type cytokinins. The atipt2 9 double mutant, on the other hand, lacked isopentenyl- and cis-hydroxy isopentenyl-tRNA, and cZ-type cytokinins. These results indicate that whereas ATP/ADP IPTs are responsible for the bulk of isopentenyladenine- and tZ-type cytokinin synthesis, tRNA IPTs are required for cZ-type cytokinin production. This work clarifies the long-standing questions of the biosynthetic routes for isopentenyladenine-, tZ-, and cZ-type cytokinin production.

• Gene trapping in Arabidopsis reveals genes involved in vascular development.

  Authors: Shingo Nagawa, Shinichirou Sawa, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Hiroo Fukuda

  Plant & cell physiology. 11/2006; 47(10):1394-405.

  The procambium is made up of stem cells that give rise to various vascular cells in plants. To understand the molecular nature of procambium cells, we tried to identify genes that characterizeThe procambium is made up of stem cells that give rise to various vascular cells in plants. To understand the molecular nature of procambium cells, we tried to identify genes that characterize procambium cells using Arabidopsis gene trap lines. Among 26,000 gene trap lines, we found 67 lines in which beta-glucuronidase (GUS) staining occurred along vascular tissues in cotyledons and/or adult leaves. Although four gene trap lines showed procambium-preferential GUS expression, their expression patterns differed from each other during procambium development in root tips and young rosette leaves. Genomic regions flanking the gene trap insertion points in 25 of the 67 lines were determined, including three lines showing preferential GUS staining of the procambium. The three procambium-related genes encoded PINHEAD, katanin and an unknown DUF740 domain-containing protein. We discuss procambium development based on the functions and the differential GUS staining patterns of the procambium-related genes.

• Identification of a Sed5-like SNARE gene LjSYP32-1 that contributes to nodule tissue formation of Lotus japonicus.

  Authors: Ha Thu Mai, Mika Nomura, Kaoru Takegawa, Erika Asamizu, Syusei Sato, Tomohiko Kato, Satoshi Tabata, Shigeyuki Tajima

  Plant & cell physiology. 08/2006; 47(7):829-38.

  We identified a Sed5-like clone LjSYP32-1 which contributes to nodule tissue formation and plant growth in Lotus japonicus. In the L. japonicus expressed sequence tag (EST) clone databases of KazusaWe identified a Sed5-like clone LjSYP32-1 which contributes to nodule tissue formation and plant growth in Lotus japonicus. In the L. japonicus expressed sequence tag (EST) clone databases of Kazusa DNA Research Institute, another syntaxin-related clone (LjSYP32-2) was also detected, and the nucleotide and amino acid sequences of these two clone are very similar to each other. Real-time PCR and promoter analysis indicated that expression of LjSYP32-1 was dominant compared with LjSYP32-2 in the various plant organs. Promoter analysis and in situ hybridization revealed that LjSYP32-1 was expressed significantly in the inner cortex cell layer surrounding the infected zone of young nodules and in the meristem area of developing lateral root. To explore the function and physiological role of LjSYP32-1 in nodules and other plant organs, stable transformation lines of L. japonicus expressing either sense or antisense LjSYP32-1 were prepared. The antisense plants showed a significantly retarded plant growth phenotype, suggesting a role for LjSYP32-1 in supporting plant growth. In the same transgenic lines, the plants were capable of forming nodules, but the acetylene reduction activity was reduced by around 50% per plant. The nodules were much smaller and some nodules were fused to each other by sharing the inner cortex. The rate of occurrence of such irregular nodules was twice that observed in wild-type plants. The data suggest that LjSYP32-1 contributes to the support of plant growth and normal nodule tissue differentiation.

• RNA interference of the Arabidopsis putative transcription factor TCP16 gene results in abortion of early pollen development.

  Authors: Taito Takeda, Kazuo Amano, Masa-aki Ohto, Kenzo Nakamura, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Chiharu Ueguchi

  Plant molecular biology. 06/2006; 61(1-2):165-77.

  Pollen development is a fundamental and essential biological process in seed plants. Pollen mother cells generated in anthers undergo meiosis, which gives rise to haploid microspores. The haploidPollen development is a fundamental and essential biological process in seed plants. Pollen mother cells generated in anthers undergo meiosis, which gives rise to haploid microspores. The haploid cells then develop into mature pollen grains through two mitotic cell divisions. Although several sporophytic and gametophytic mutations affecting male gametogenesis have been identified and analyzed, little is known about the underlying molecular mechanism. In this study, we investigated the function of the TCP16 gene, which encodes a putative transcription factor. Expression analysis of the promoter::GUS fusion gene revealed that TCP16 transcription occurred predominantly in developing microspores. GUS expression began at the tetrad stage and markedly increased in an early unicellular stage. Transgenic plants harboring a TCP16 RNA interference (RNAi) construct generated equal amounts of normal and abnormal pollen grains. The abnormal pollen grains exhibited morphological abnormality and degeneration of genomic DNA. The defective phenotype of the RNAi plants was first detectable at the middle of the unicellular stage. Our results therefore suggest that TCP16, a putative transcription factor, plays a crucial role in early processes in pollen development.

• Distinct and overlapping roles of two gibberellin 3-oxidases in Arabidopsis development.

  Authors: Melissa G Mitchum, Shinjiro Yamaguchi, Atsushi Hanada, Ayuko Kuwahara, Yasushi Yoshioka, Tomohiko Kato, Satoshi Tabata, Yuji Kamiya, Tai-ping Sun

  The Plant journal : for cell and molecular biology. 04/2006; 45(5):804-18.

  Gibberellin (GA) 3-oxidase, a class of 2-oxoglutarate-dependent dioxygenases, catalyzes the conversion of precursor GAs to their bioactive forms, thereby playing a direct role in determining theGibberellin (GA) 3-oxidase, a class of 2-oxoglutarate-dependent dioxygenases, catalyzes the conversion of precursor GAs to their bioactive forms, thereby playing a direct role in determining the levels of bioactive GAs in plants. Gibberellin 3-oxidase in Arabidopsis is encoded by a multigene family consisting of at least four members, designated AtGA3ox1 to AtGA3ox4. It has yet to be investigated how each AtGA3ox gene contributes to optimizing bioactive GA levels during growth and development. Using quantitative real-time PCR analysis, we have shown that each AtGA3ox gene exhibits a unique organ-specific expression pattern, suggesting distinct developmental roles played by individual AtGA3ox members. To investigate the sites of synthesis of bioactive GA in plants, we generated transgenic Arabidopsis that carried AtGA3ox1-GUS and AtGA3ox2-GUS fusions. Comparisons of the GUS staining patterns of these plants with that of AtCPS-GUS from previous studies revealed the possible physical separation of the early and late stages of the GA pathway in roots. Phenotypic characterization and quantitative analysis of the endogenous GA content of ga3ox1 and ga3ox2 single and ga3ox1/ga3ox2 double mutants revealed distinct as well as overlapping roles of AtGA3ox1 and AtGA3ox2 in Arabidopsis development. Our results show that AtGA3ox1 and AtGA3ox2 are responsible for the synthesis of bioactive GAs during vegetative growth, but that they are dispensable for reproductive development. The stage-specific severe GA-deficient phenotypes of the ga3ox1/ga3ox2 mutant suggest that AtGA3ox3 and AtGA3ox4 are tightly regulated by developmental cues; AtGA3ox3 and AtGA3ox4 are not upregulated to compensate for GA deficiency during vegetative growth of the double mutant.

• Genetics of symbiosis in Lotus japonicus: recombinant inbred lines, comparative genetic maps, and map position of 35 symbiotic loci.

  Authors: Niels Sandal, Thomas Rørby Petersen, Jeremy Murray, Yosuke Umehara, Bogumil Karas, Koji Yano, Hirotaka Kumagai, Makoto Yoshikawa, Katsuharu Saito, Masaki Hayashi [......] Shingo Hata, Norio Suganuma, Hiroshi Kouchi, Shinji Kawasaki, Satoshi Tabata, Makoto Hayashi, Martin Parniske, Krzysztof Szczyglowski, Masayoshi Kawaguchi, Jens Stougaard

  Molecular plant-microbe interactions : MPMI. 02/2006; 19(1):80-91.

  Development of molecular tools for the analysis of the plant genetic contribution to rhizobial and mycorrhizal symbiosis has provided major advances in our understanding of plant-microbeDevelopment of molecular tools for the analysis of the plant genetic contribution to rhizobial and mycorrhizal symbiosis has provided major advances in our understanding of plant-microbe interactions, and several key symbiotic genes have been identified and characterized. In order to increase the efficiency of genetic analysis in the model legume Lotus japonicus, we present here a selection of improved genetic tools. The two genetic linkage maps previously developed from an interspecific cross between L. japonicus Gifu and L. filicaulis, and an intraspecific cross between the two ecotypes L. japonicus Gifu and L. japonicus MG-20, were aligned through a set of anchor markers. Regions of linkage groups, where genetic resolution is obtained preferentially using one or the other parental combination, are highlighted. Additional genetic resolution and stabilized mapping populations were obtained in recombinant inbred lines derived by a single seed descent from the two populations. For faster mapping of new loci, a selection of reliable markers spread over the chromosome arms provides a common framework for more efficient identification of new alleles and new symbiotic loci among uncharacterized mutant lines. Combining resources from the Lotus community, map positions of a large collection of symbiotic loci are provided together with alleles and closely linked molecular markers. Altogether, this establishes a common genetic resource for Lotus spp. A web-based version will enable this resource to be curated and updated regularly.

• Cell-to-cell movement of the CAPRICE protein in Arabidopsis root epidermal cell differentiation.

  Authors: Tetsuya Kurata, Tetsuya Ishida, Chie Kawabata-Awai, Masahiro Noguchi, Sayoko Hattori, Ryosuke Sano, Ryoko Nagasaka, Rumi Tominaga, Yoshihiro Koshino-Kimura, Tomohiko Kato, Shusei Sato, Satoshi Tabata, Kiyotaka Okada, Takuji Wada

  Development (Cambridge, England). 01/2006; 132(24):5387-98.

  CAPRICE (CPC), a small, R3-type Myb-like protein, is a positive regulator of root hair development in Arabidopsis. Cell-to-cell movement of CPC is important for the differentiation of epidermal cellsCAPRICE (CPC), a small, R3-type Myb-like protein, is a positive regulator of root hair development in Arabidopsis. Cell-to-cell movement of CPC is important for the differentiation of epidermal cells into trichoblasts (root hair cells). CPC is transported from atrichoblasts (hairless cells), where it is expressed, to trichoblasts, and generally accumulates in their nuclei. Using truncated versions of CPC fused to GFP, we identified a signal domain that is necessary and sufficient for CPC cell-to-cell movement. This domain includes the N-terminal region and a part of the Myb domain. Amino acid substitution experiments indicated that W76 and M78 in the Myb domain are critical for targeted transport, and that W76 is crucial for the nuclear accumulation of CPC:GFP. To evaluate the tissue-specificity of CPC movement, CPC:GFP was expressed in the stele using the SHR promoter and in trichoblasts using the EGL3 promoter. CPC:GFP was able to move from trichoblasts to atrichoblasts but could not exit from the stele, suggesting the involvement of tissue-specific regulatory factors in the intercellular movement of CPC. Analyses with a secretion inhibitor, Brefeldin A, and with an rhd3 mutant defective in the secretion process in root epidermis suggested that intercellular CPC movement is mediated through plasmodesmata. Furthermore, the fusion of CPC to tandem-GFPs defined the capability of CPC to increase the size exclusion limit of plasmodesmata.

• An important role of phosphatidic acid in ABA signaling during germination in Arabidopsis thaliana.

  Authors: Takeshi Katagiri, Kanako Ishiyama, Tomohiko Kato, Satoshi Tabata, Masatomo Kobayashi, Kazuo Shinozaki

  The Plant journal : for cell and molecular biology. 08/2005; 43(1):107-17.

  Phosphatidic acid (PA) functions as a lipid signaling molecule in plants. Physiological analysis showed that PA triggers early signal transduction events that lead to responses to abscisic acid (ABA)Phosphatidic acid (PA) functions as a lipid signaling molecule in plants. Physiological analysis showed that PA triggers early signal transduction events that lead to responses to abscisic acid (ABA) during seed germination. We measured PA production during seed germination and found increased PA levels during early germination. To investigate the role of PA during seed germination, we focused on the PA catabolic enzyme lipid phosphate phosphatase (LPP). LPP catalyzes the conversion of PA to diacylglycerol (DAG). There are 4 LPP genes in the Arabidopsis genome. Among them, AtLPP2 and AtLPP3 are expressed during seed germination. Two AtLPP2 T-DNA insertional mutants (lpp2-1 and lpp2-2) showed hypersensitivity to ABA and significant PA accumulation during germination. Furthermore, double-mutant analysis showed that ABA-insensitive 4 (ABI4) is epistatic to AtLPP2 but ABA-insensitive 3 (ABI3) is not. These results suggest that PA is involved in ABA signaling and that AtLPP2 functions as a negative regulator upstream of ABI4, which encodes an AP2-type transcription factor, in ABA signaling during germination.

• Roles of Arabidopsis AtREV1 and AtREV7 in translesion synthesis.

  Authors: Shinya Takahashi, Ayako Sakamoto, Shusei Sato, Tomohiko Kato, Satoshi Tabata, Atsushi Tanaka

  Plant physiology. 07/2005; 138(2):870-81.

  Plants have mechanisms for repairing and tolerating detrimental effects by various DNA damaging agents. A tolerance pathway that has been predicted to be present in higher plants is translesionPlants have mechanisms for repairing and tolerating detrimental effects by various DNA damaging agents. A tolerance pathway that has been predicted to be present in higher plants is translesion synthesis (TLS), which is catalyzed by polymerases. In Arabidopsis (Arabidopsis thaliana), however, the only gene known to be involved in TLS is the Arabidopsis homolog of REV3, AtREV3, which is a putative catalytic subunit of Arabidopsis DNA polymerase zeta. A disrupted mutant of AtREV3, rev3, was previously found to be highly sensitive to ultraviolet-B (UV-B) and various DNA damaging agents. REV1 and REV7 are thought to be components of translesion synthesis in plants. In this study, we identified the Arabidopsis homologs of REV1 and REV7 (AtREV1 and AtREV7). Several mutants carrying disrupted AtREV1 and AtREV7 genes were isolated from Arabidopsis T-DNA-inserted lines. An AtREV1-disrupted mutant, rev1, was found to be moderately sensitive to UV-B and DNA cross-linkers. A rev1rev3 double mutant, like rev3, showed high sensitivity to UV-B, gamma-rays, and DNA cross-linkers. An AtREV7-disrupted mutant, rev7, was possibly sensitive to cis-diamminedichloroplatinum(II), a kind of DNA cross-linker, but it was not sensitive to acute UV-B and gamma-ray irradiation. On the other hand, the aerial growth of rev7, like the aerial growth of rev1 and rev3, was inhibited by long-term UV-B. These results suggest that a TLS mechanism exists in a higher plant and show that AtREV1 and AtREV7 have important roles in tolerating exposure to DNA-damaging agents.

• Arabidopsis Rad51B is important for double-strand DNA breaks repair in somatic cells.

  Authors: Keishi Osakabe, Kiyomi Abe, Hiroaki Yamanouchi, Toshio Takyuu, Terutaka Yoshioka, Yuji Ito, Tomohiko Kato, Satoshi Tabata, Shunsuke Kurei, Yasushi Yoshioka, Yasunori Machida, Motoaki Seki, Masatomo Kobayashi, Kazuo Shinozaki, Hiroaki Ichikawa, Seiichi Toki

  Plant molecular biology. 05/2005; 57(6):819-33.

  Rad51 paralogs belong to the Rad52 epistasis group of proteins and are involved in homologous recombination (HR), especially the assembly and stabilization of Rad51, which is a homolog of RecA inRad51 paralogs belong to the Rad52 epistasis group of proteins and are involved in homologous recombination (HR), especially the assembly and stabilization of Rad51, which is a homolog of RecA in eukaryotes. We previously cloned and characterized two RAD51 paralogous genes in Arabidopsis, named AtRAD51C and AtXRCC3, which are considered the counterparts of human RAD51C and XRCC3, respectively. Here we describe the identification of RAD51B homologue in Arabidopsis, AtRAD51B. We found a higher expression of AtRAD51B in flower buds and roots. Expression of AtRAD51B was induced by genotoxic stresses such as ionizing irradiation and treatment with a cross-linking reagent, cisplatin. Yeast two-hybrid analysis showed that AtRad51B interacted with AtRad51C. We also found and characterized T-DNA insertion mutant lines. The mutant lines were devoid of AtRAD51B expression, viable and fertile. The mutants were moderately sensitive to gamma-ray and hypersensitive to cisplatin. Our results suggest that AtRAD51B gene product is involved in the repair of double-strand DNA breaks (DSBs) via HR.

• A vacuolar processing enzyme, deltaVPE, is involved in seed coat formation at the early stage of seed development.

  Authors: Satoru Nakaune, Kenji Yamada, Maki Kondo, Tomohiko Kato, Satoshi Tabata, Mikio Nishimura, Ikuko Hara-Nishimura

  The Plant cell. 04/2005; 17(3):876-87.

  Vacuolar processing enzyme (VPE) is a Cys proteinase responsible for the maturation of vacuolar proteins. Arabidopsis thaliana deltaVPE, which was recently found in the database, was specifically andVacuolar processing enzyme (VPE) is a Cys proteinase responsible for the maturation of vacuolar proteins. Arabidopsis thaliana deltaVPE, which was recently found in the database, was specifically and transiently expressed in two cell layers of the seed coat (ii2 and ii3) at an early stage of seed development. At this stage, cell death accompanying cell shrinkage occurs in the ii2 layer followed by cell death in the ii3 layer. In a deltaVPE-deficient mutant, cell death of the two layers of the seed coat was delayed. Immunocytochemical analysis localized deltaVPE to electron-dense structures inside and outside the walls of seed coat cells that undergo cell death. Interestingly, deltaVPE in the precipitate fraction from young siliques exhibits caspase-1-like activity, which has been detected in various types of plant cell death. Our results suggest that, at the early stage of seed development, deltaVPE is involved in cell death of limited cell layers, the purpose of which is to form a seed coat.