title: Dominant and recessive mutations in the Raf-like kinase HT1 gene completely disrupt stomatal responses to CO2 in Arabidopsis.
abstract: 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.
authors.affiliation: Department of Biology, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Mimi
authors.initials: M
authors.lastname: Hashimoto-Sugimoto
authors.affiliation: Department of Biology, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Juntaro
authors.initials: J
authors.lastname: Negi
authors.affiliation: Department of Biology, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Keina
authors.initials: K
authors.lastname: Monda
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha Kashiwa, Chiba 277-8562, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Higaki
authors.affiliation: Department of Biotechnology, Faculty of Engineering, Biotechnology Research Center, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Isogai
authors.affiliation: Department of Biology, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha Kashiwa, Chiba 277-8562, Japan.
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Hasezawa
authors.affiliation: Department of Biology, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan. iba.koh.727@m.kyushu-u.ac.jp.
authors.forename: Koh
authors.initials: K
authors.lastname: Iba
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002245:Carbon Dioxide / Q000378:metabolism*; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D054046:Plant Stomata / Q000201:enzymology / Q000502:physiology; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D002245:Carbon Dioxide; C000610355:HT1 protein, Arabidopsis; D011494:Protein Kinases
keywords: ABA; Arabidopsis; CO2 response; HIGH LEAF TEMPERATURE 1; Light; MAPKKK; Raf-like kinase; stomatal control.