title: The Arabidopsis small G protein ROP2 is activated by light in guard cells and inhibits light-induced stomatal opening.
abstract: ROP small G proteins function as molecular switches in diverse signaling processes. Here, we investigated signals that activate ROP2 in guard cells. In guard cells of Vicia faba expressing Arabidopsis thaliana constitutively active (CA) ROP2 fused to red fluorescent protein (RFP-CA-ROP2), fluorescence localized exclusively at the plasma membrane, whereas a dominant negative version of RFP-ROP2 (DN-ROP2) localized in the cytoplasm. In guard cells expressing green fluorescent protein-ROP2, the relative fluorescence intensity at the plasma membrane increased upon illumination, suggesting that light activates ROP2. Unlike previously reported light-activated factors, light-activated ROP2 inhibits rather than accelerates light-induced stomatal opening; stomata bordered by guard cells transformed with CA-rop2 opened less than controls upon light irradiation. When introduced into guard cells together with CA-ROP2, At RhoGDI1, which encodes a guanine nucleotide dissociation inhibitor, inhibited plasma membrane localization of CA-ROP2 and abolished the inhibitory effect of CA-ROP2 on light-induced stomatal opening, supporting the negative effect of active ROP2 on stomatal opening. Mutant rop2 Arabidopsis guard cells showed phenotypes similar to those of transformed V. faba guard cells; CA-rop2 stomata opened more slowly and to a lesser extent, and DN-rop2 stomata opened faster than wild-type stomata in response to light. Moreover, in rop2 knockout plants, stomata opened faster and to a greater extent than wild-type stomata in response to light. Thus, ROP2 is a light-activated negative factor that attenuates the extent of light-induced changes in stomatal aperture. The inhibition of light-induced stomatal opening by light-activated ROP2 suggests the existence of feedback regulatory mechanisms through which stomatal apertures may be finely controlled.
authors.affiliation: POSTECH-UZH Global Research Laboratories, Division of Molecular Life Sciences, POSTECH, Pohang 790-784, Korea.
authors.forename: Byeong Wook
authors.initials: BW
authors.lastname: Jeon
authors.forename: Jae-Ung
authors.initials: JU
authors.lastname: Hwang
authors.forename: Youngkyu
authors.initials: Y
authors.lastname: Hwang
authors.forename: Won-Yong
authors.initials: WY
authors.lastname: Song
authors.forename: Ying
authors.initials: Y
authors.lastname: Fu
authors.forename: Ying
authors.initials: Y
authors.lastname: Gu
authors.forename: Fang
authors.initials: F
authors.lastname: Bao
authors.forename: Daeshik
authors.initials: D
authors.lastname: Cho
authors.forename: June M
authors.initials: JM
authors.lastname: Kwak
authors.forename: Zhenbiao
authors.initials: Z
authors.lastname: Yang
authors.forename: Youngsook
authors.initials: Y
authors.lastname: Lee
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000528:radiation effects; D004789:Enzyme Activation / Q000528:radiation effects; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008027:Light; D050505:Mutant Proteins / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D054046:Plant Stomata / Q000166:cytology* / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects*; D018526:Plant Transpiration / Q000528:radiation effects; D021381:Protein Transport / Q000528:radiation effects; D013696:Temperature; D031307:Vicia faba / Q000166:cytology / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; D019204:GTP-Binding Proteins; D050505:Mutant Proteins; C499714:AT1G20090 protein, Arabidopsis