Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Juntaro Negi Last modified date:2020.06.18

Associate Professor / Informational biology / Department of Biology / Faculty of Sciences

1. Juntaro Negi, Shintaro Munemasa, Boseok Song, Ryosuke Tadakuma, Mayumi Fujita, Tamar Azoulay-Shemer, Cawas B. Engineer, Kensuke Kusumi, Ikuo Nishida, Julian I. Schroeder, Koh Iba, Eukaryotic lipid metabolic pathway is essential for functional chloroplasts and CO2 and light responses in Arabidopsis guard cells, Proceedings of the National Academy of Sciences of the United States of America, 10.1073/pnas.1810458115, 115, 36, 9038-9043, 2018.09.
2. Kusumi, K.,Hashimura, A., Yamamoto, Y., Negi, J. and Iba, K. , Contribution of the S-type Anion Channel SLAC1 to Stomatal Control and Its Dependence on Developmental Stage in Rice, PLANT AND CELL PHYSIOLOGY, 10.1093/pcp/pcx142, 58, 12, 2085-2094, 2017.12.
3. Takahashi, S., Monda, K., Higaki, T., Negi, J., Hashimoto-Sugimoto, M., Hasezawa, S. and Iba, K., Differential effects of phosphatidylinositol 4-kinase (PI4K) and 3-kinase (PI3K) inhibitors on stomatal responses to environmental signals., Front. Plant Sci., doi: 10.3389/fpls.2017.00677, 8, 677, 2017.05.
4. Mimi Hashimoto-Sugimoto, Juntaro Negi, Keina Monda, Takumi Higaki, Yasuhiro Isogai, Toshiaki Nakano, Seiichiro Hasezawa, Koh Iba, Dominant and recessive mutations in the Raf-like kinase HT1 gene completely disrupt stomatal responses to CO2 in Arabidopsis, JOURNAL OF EXPERIMENTAL BOTANY, 10.1093/jxb/erw134, 67, 11, 3251-3261, 2016.05, [URL], HT1 (HIGH LEAF TEMPERATURE 1) is the first component associated with changes in stomatal aperture in response to CO2 to be isolated by forward genetic screening. The HT1 gene encodes a protein kinase expressed mainly in guard cells. The loss-of-function ht1-1 and ht1-2 mutants in Arabidopsis thaliana have CO2-hypersensitive stomatal closure with concomitant reductions in their kinase activities in vitro. In addition to these mutants, in this study we isolate or obtaine five new ht1 alleles (ht1-3, ht1-4, ht1-5, ht1-6, and ht1-7). Among the mutants, only ht1-3 has a dominant mutant phenotype and has widely opened stomata due to CO2 insensitivity. The ht1-3 mutant has a missense mutation affecting a non-conserved residue (R102K), whereas the other six recessive mutants have mutations in highly conserved residues in the catalytic domains required for kinase activity. We found that the dominant mutation does not affect the expression of HT1 or the ability to phosphorylate casein, a universal kinase substrate, but it does affect autophosphorylation activity in vitro. A 3D structural model of HT1 also shows that the R102 residue protrudes from the surface of the kinase, implying a role for the formation of oligomers and/or interaction with its targets. We demonstrate that both the loss-of-function and gain-of-function ht1 mutants have completely disrupted CO2 responses, although they have normal responses to ABA. Furthermore, light-induced stomatal opening is smaller in ht1-3 and much smaller in ht1-2. Taken together, these results indicate that HT1 is a critical regulator for CO2 signaling and is partially involved in the light-induced stomatal opening pathway..
5. Keina Monda, Hiromitsu Araki, Satoru Kuhara, Genki Ishigaki, Ryo Akashi, Juntaro Negi, Mikiko Kojima, Hitoshi Sakakibara, Sho Takahashi, Mimi Hashimoto-Sugimoto, Nobuharu Goto, Koh Iba, Enhanced Stomatal Conductance by a Spontaneous Arabidopsis Tetraploid, Me-0, Results from Increased Stomatal Size and Greater Stomatal Aperture, PLANT PHYSIOLOGY, 10.1104/pp.15.01450, 170, 3, 1435-1444, 2016.03, [URL], The rate of gas exchange in plants is regulated mainly by stomatal size and density. Generally, higher densities of smaller stomata are advantageous for gas exchange; however, it is unclear what the effect of an extraordinary change in stomatal size might have on a plant’s gas-exchange capacity. We investigated the stomatal responses to CO2 concentration changes among 374 Arabidopsis (Arabidopsis thaliana) ecotypes and discovered that Mechtshausen (Me-0), a natural tetraploid ecotype, has significantly larger stomata and can achieve a high stomatal conductance. We surmised that the cause of the increased stomatal conductance is tetraploidization; however, the stomatal conductance of another tetraploid accession, tetraploid Columbia (Col), was not as high as that in Me-0. One difference between these two accessions was the size of their stomatal apertures. Analyses of abscisic acid sensitivity, ion balance, and gene expression profiles suggested that physiological or genetic factors restrict the stomatal opening in tetraploid Col but not in Me-0. Our results show that Me-0 overcomes the handicap of stomatal opening that is typical for tetraploids and achieves higher stomatal conductance compared with the closely related tetraploid Col on account of larger stomatal apertures. This study provides evidence for whether larger stomatal size in tetraploids of higher plants can improve stomatal conductance..
6. Yoshiko Yamamoto, Juntaro Negi, Cun Wang, Yasuhiro Isogai, Julian Schroeder, Koh Iba, The Transmembrane Region of Guard Cell SLAC1 Channels Perceives CO2 Signals via an ABA-Independent Pathway in Arabidopsis, PLANT CELL, 10.1105/tpc.15.00583, 28, 2, 557-567, 2016.02, [URL].
7. Sho Takahashi, Keina Monda, Juntaro Negi, Fumitaka Konishi, Shinobu Ishikawa, Mimi Hashimoto-Sugimoto, Nobuharu Goto, Koh Iba, Natural Variation in Stomatal Responses to Environmental Changes among Arabidopsis thaliana Ecotypes, PLOS ONE, 10.1371/journal.pone.0117449, 10, 2, 2015.02, [URL].
8. Takamitsu Kurusu, Katsunori Saito, Sonoko Horikoshi, Shigeru Hanamata, Juntaro Negi, Chikako Yagi, Nobutaka Kitahata, Koh Iba, Kazuyuki Kuchitsu, An S-Type Anion Channel SLAC1 Is Involved in Cryptogein-Induced Ion Fluxes and Modulates Hypersensitive Responses in Tobacco BY-2 Cells., PLOS One , 10.1371, 8, 8, 2013.08, [URL].
9. Mimi Hashimoto-Sugimoto, Takumi Higaki, Takashi Yaeno, Ayako Nagami, Mari Irie, Miho Fujimi, Megumi Miyamoto, Kae Akita, Juntaro Negi, Ken Shirasu, Seiichiro Hasezawa, Koh Iba, A Munc13-like protein in Arabidopsis mediates H+-ATPase translocation that is essential for stomatal responses, Nature Commun. , 10.1038/ncomms3215, 4, 2215, 2013.07, [URL].
10. Juntaro Negi, Kosuke Moriwaki, Mineko Konishi, Ryusuke Yokoyama, Toshiaki Nakano, kensuke kusumi, Mimi Hashimoto-Sugimoto, Julian I. Schroeder, Kazuhiko Nishitani, Shuichi Yanagisawa, Koh Iba, A Dof Transcription Factor, SCAP1, Is Essential for the Development of Functional Stomata in Arabidopsis., Current Biology, 23, 6, 479-484, 2013.03.
11. Benjamin Brandt, Dennis E. Brodsky, Shaowu Xue, Juntaro Negi, Koh Iba, Jaakko Kangasjärvi, Majid Ghassemian, Aaron B. Stephan, Honghong Hu, Julian I. Schroeder, Reconstitution of abscisic acid activation of SLAC1 anion channel by CPK6 and OST1 kinases and branched ABI1 PP2C phosphatase action., Proceedings of the National Academy of Sciences of the United States of America, 109, 26, 10593-10598, 2012.06, The plant hormone abscisic acid (ABA) is produced in response to abiotic stresses and mediates stomatal closure in response to drought via recently identified ABA receptors (pyrabactin resistance/regulatory component of ABA receptor; PYR/RCAR). SLAC1 encodes a central guard cell S-type anion channel that mediates ABA-induced stomatal closure. Coexpression of the calcium-dependent protein kinase 21 (CPK21), CPK23, or the Open Stomata 1 kinase (OST1) activates SLAC1 anion currents. However, reconstitution of ABA activation of any plant ion channel has not yet been attained. Whether the known core ABA signaling components are sufficient for ABA activation of SLAC1 anion channels or whether additional components are required remains unknown. The Ca(2+)-dependent protein kinase CPK6 is known to function in vivo in ABA-induced stomatal closure. Here we show that CPK6 robustly activates SLAC1-mediated currents and phosphorylates the SLAC1 N terminus. A phosphorylation site (S59) in SLAC1, crucial for CPK6 activation, was identified. The group A PP2Cs ABI1, ABI2, and PP2CA down-regulated CPK6-mediated SLAC1 activity in oocytes. Unexpectedly, ABI1 directly dephosphorylated the N terminus of SLAC1, indicating an alternate branched early ABA signaling core in which ABI1 targets SLAC1 directly (down-regulation). Furthermore, here we have successfully reconstituted ABA-induced activation of SLAC1 channels in oocytes using the ABA receptor pyrabactin resistant 1 (PYR1) and PP2C phosphatases with two alternate signaling cores including either CPK6 or OST1. Point mutations in ABI1 disrupting PYR1-ABI1 interaction abolished ABA signal transduction. Moreover, by addition of CPK6, a functional ABA signal transduction core from ABA receptors to ion channel activation was reconstituted without a SnRK2 kinase..
12. Keina Monda, Juntaro Negi, Atsuhiro Iio, kensuke kusumi, Mikiko Kojima, Mimi Hashimoto, Hitoshi Sakakibara, Koh Iba, Environmental regulation of stomatal response in the Arabidopsis Cvi-0 ecotype, PLANTA, 10.1007/s00425-011-1424-x, 234, 3, 555-563, 2011.09, The Arabidopsis Cape Verde Islands (Cvi-0) ecotype is known to differ from other ecotypes with respect to environmental stress responses. We analyzed the stomatal behavior of Cvi-0 plants, in response to environmental signals. We investigated the responses of stomatal conductance and aperture to high [CO₂] in the Cvi-0 and Col-0 ecotypes. Cvi-0 showed constitutively higher stomatal conductance and more stomatal opening than Col-0. Cvi-0 stomata opened in response to light, but the response was slow. Under low humidity, stomatal opening was increased in Cvi-0 compared to Col-0. We then assessed whether low humidity affects endogenous ABA levels in Cvi-0. In response to low humidity, Cvi-0 had much higher ABA levels than Col-0. However, epidermal peels experiments showed that Cvi-0 stomata were insensitive to ABA. Measurements of organic and inorganic ions in Cvi-0 guard cell protoplasts indicated an over-accumulation of osmoregulatory anions (malate and Cl⁻). This irregular anion homeostasis in the guard cells may explain the constitutive stomatal opening phenotypes of the Cvi-0 ecotype, which lacks high [CO₂]-induced and low humidity-induced stomatal closure..
13. Juntaro Negi, Osamu Matsuda, Takashi Nagasawa, Yasuhiro Oba, Hideyuki Takahashi, Maki Kawai-Yamada, Hirofumi Uchimiya, Mimi Hashimoto, Koh Iba, CO2 regulator SLAC1 and its homologues are essential for anion homeostasis in plant cells, Nature, 452, 27, 483-486, 2008.03.
14. Mimi Hashimoto, Juntaro Negi, Jared Young, Maria Israelsson, Julian I. Schroeder, Koh Iba, Arabidopsis HT1 kinase controls stomatal movements in response to CO2., Nature Cell Biology, 8, 391-397, 2006.04, Guard cells, which form stomata in leaf epidermes, sense a multitude of environmental signals and integrate this information to regulate stomatal movements. Compared with the advanced understanding of light and water stress responses in guard cells, the molecular mechanisms that underlie stomatal CO(2) signalling have remained relatively obscure. With a high-throughput leaf thermal imaging CO(2) screen, we report the isolation of two allelic Arabidopsis mutants (high leaf temperature 1; ht1-1 and ht1-2) that are altered in their ability to control stomatal movements in response to CO(2). The strong allele, ht1-2, exhibits a markedly impaired CO(2) response but shows functional responses to blue light, fusicoccin and abscisic acid (ABA), indicating a role for HT1 in stomatal CO(2) signalling. HT1 encodes a protein kinase that is expressed mainly in guard cells. Phosphorylation assays demonstrate that the activity of the HT1 protein carrying the ht1-1 or ht1-2 mutation is greatly impaired or abolished, respectively. Furthermore, dominant-negative HT1(K113W) transgenic plants, which lack HT1 kinase activity, show a disrupted CO(2) response. These findings indicate that the HT1 kinase is important for regulation of stomatal movements and its function is more pronounced in response to CO(2) than it is to ABA or light..