title: Roles of the different components of magnesium chelatase in abscisic acid signal transduction.
abstract: The H subunit of Mg-chelatase (CHLH) was shown to regulate abscisic acid (ABA) signaling and the I subunit (CHLI) was also reported to modulate ABA signaling in guard cells. However, it remains essentially unknown whether and how the Mg-chelatase-catalyzed Mg-protoporphyrin IX-production differs from ABA signaling. Using a newly-developed surface plasmon resonance system, we showed that ABA binds to CHLH, but not to the other Mg-chelatase components/subunits CHLI, CHLD (D subunit) and GUN4. A new rtl1 mutant allele of the CHLH gene in Arabidopsis thaliana showed ABA-insensitive phenotypes in both stomatal movement and seed germination. Upregulation of CHLI1 resulted in ABA hypersensitivity in seed germination, while downregulation of CHLI conferred ABA insensitivity in stomatal response in Arabidopsis. We showed that CHLH and CHLI, but not CHLD, regulate stomatal sensitivity to ABA in tobacco (Nicotiana benthamiana). The overexpression lines of the CHLD gene showed wild-type ABA sensitivity in Arabidopsis. Both the GUN4-RNA interference and overexpression lines of Arabidopsis showed wild-type phenotypes in the major ABA responses. These findings provide clear evidence that the Mg-chelatase-catalyzed Mg-ProtoIX production is distinct from ABA signaling, giving information to understand the mechanism by which the two cellular processes differs at the molecular level.
authors.affiliation: MOE Systems Biology and Bioinformatics Laboratory, School of Life Sciences, Tsinghua University, Beijing, China.
authors.forename: Shu-Yuan
authors.initials: SY
authors.lastname: Du
authors.forename: Xiao-Feng
authors.initials: XF
authors.lastname: Zhang
authors.forename: Zekuan
authors.initials: Z
authors.lastname: Lu
authors.forename: Qi
authors.initials: Q
authors.lastname: Xin
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wu
authors.forename: Tao
authors.initials: T
authors.lastname: Jiang
authors.forename: Yan
authors.initials: Y
authors.lastname: Lu
authors.forename: Xiao-Fang
authors.initials: XF
authors.lastname: Wang
authors.forename: Da-Peng
authors.initials: DP
authors.lastname: Zhang
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D017343:Genes, Plant; D008190:Lyases / Q000378:metabolism*; D011485:Protein Binding; D015398:Signal Transduction; D015854:Up-Regulation
chemical_list: D000040:Abscisic Acid; D008190:Lyases; C086788:magnesium chelatase