title: Mg-chelatase H subunit affects ABA signaling in stomatal guard cells, but is not an ABA receptor in Arabidopsis thaliana.
abstract: Mg-chelatase H subunit (CHLH) is a multifunctional protein involved in chlorophyll synthesis, plastid-to-nucleus retrograde signaling, and ABA perception. However, whether CHLH acts as an actual ABA receptor remains controversial. Here we present evidence that CHLH affects ABA signaling in stomatal guard cells but is not itself an ABA receptor. We screened ethyl methanesulfonate-treated Arabidopsis thaliana plants with a focus on stomatal aperture-dependent water loss in detached leaves and isolated a rapid transpiration in detached leaves 1 (rtl1) mutant that we identified as a novel missense mutant of CHLH. The rtl1 and CHLH RNAi plants showed phenotypes in which stomatal movements were insensitive to ABA, while the rtl1 phenotype showed normal sensitivity to ABA with respect to seed germination and root growth. ABA-binding analyses using (3)H-labeled ABA revealed that recombinant CHLH did not bind ABA, but recombinant pyrabactin resistance 1, a reliable ABA receptor used as a control, showed specific binding. Moreover, we found that the rtl1 mutant showed ABA-induced stomatal closure when a high concentration of extracellular Ca(2+) was present and that a knockout mutant of Mg-chelatase I subunit (chli1) showed the same ABA-insensitive phenotype as rtl1. These results suggest that the Mg-chelatase complex as a whole affects the ABA-signaling pathway for stomatal movements.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Tomo
authors.initials: T
authors.lastname: Tsuzuki
authors.forename: Koji
authors.initials: K
authors.lastname: Takahashi
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Inoue
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Okigaki
authors.forename: Masakazu
authors.initials: M
authors.lastname: Tomiyama
authors.forename: Mohammad Anowar
authors.initials: MA
authors.lastname: Hossain
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Shimazaki
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Murata
authors.forename: Toshinori
authors.initials: T
authors.lastname: Kinoshita
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002734:Chlorophyll / Q000032:analysis; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test / Q000379:methods; D005822:Genetic Vectors; D018525:Germination; D008190:Lyases / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D010641:Phenotype; D018515:Plant Leaves / Q000254:growth & development; D018517:Plant Roots / Q000254:growth & development; D054046:Plant Stomata / Q000254:growth & development / Q000378:metabolism*; D018526:Plant Transpiration; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D011994:Recombinant Proteins / Q000378:metabolism; D012639:Seeds / Q000254:growth & development; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D002734:Chlorophyll; D000040:Abscisic Acid; D008190:Lyases; C561080:GUN5 protein, Arabidopsis; D002118:Calcium