title: A small GTPase activator protein interacts with cytoplasmic phytochromes in regulating root development.
abstract: Phytochromes enable plants to sense light information and regulate developmental responses. Phytochromes interact with partner proteins to transmit light signals to downstream components for plant development. PIRF1 (phytochrome-interacting ROP guanine-nucleotide exchange factor (RopGEF 1)) functions as a light-signaling switch regulating root development through the activation of ROPs (Rho-like GTPase of plant) in the cytoplasm. In vitro pulldown and yeast two-hybrid assays confirmed the interaction between PIRF1 and phytochromes. PIRF1 interacted with the N-terminal domain of phytochromes through its conserved PRONE (plant-specific ROP nucleotide exchanger) region. PIRF1 also interacted with ROPs and activated them in a phytochrome-dependent manner. The Pr form of phytochrome A enhanced the RopGEF activity of PIRF1, whereas the Pfr form inhibited it. A bimolecular fluorescence complementation analysis demonstrated that PIRF1 was localized in the cytoplasm and bound to the phytochromes in darkness but not in light. PIRF1 loss of function mutants (pirf1) of Arabidopsis thaliana showed a longer root phenotype in the dark. In addition, both PIRF1 overexpression mutants (PIRF1-OX) and phytochrome-null mutants (phyA-211 and phyB-9) showed retarded root elongation and irregular root hair formation, suggesting that PIRF1 is a negative regulator of phytochrome-mediated primary root development. We propose that phytochrome and ROP signaling are interconnected through PIRF1 in regulating the root growth and development in Arabidopsis.
authors.affiliation: Graduate School of Biotechnology and Plant Metabolism Research Center, Kyung Hee University, Yongin 446-701.
authors.forename: Dong Ho
authors.initials: DH
authors.lastname: Shin
authors.forename: Man-Ho
authors.initials: MH
authors.lastname: Cho
authors.forename: Tae-Lim
authors.initials: TL
authors.lastname: Kim
authors.forename: Jihye
authors.initials: J
authors.lastname: Yoo
authors.forename: Jeong-Il
authors.initials: JI
authors.lastname: Kim
authors.forename: Yun-Jeong
authors.initials: YJ
authors.lastname: Han
authors.forename: Pill-Soon
authors.initials: PS
authors.lastname: Song
authors.forename: Jong-Seong
authors.initials: JS
authors.lastname: Jeon
authors.forename: Seong Hee
authors.initials: SH
authors.lastname: Bhoo
authors.forename: Tae-Ryong
authors.initials: TR
authors.lastname: Hahn
mesh_terms: D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D035264:Flowers / Q000378:metabolism; D020549:GTP Phosphohydrolase Activators / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008027:Light; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D020549:GTP Phosphohydrolase Activators; D020662:Guanine Nucleotide Exchange Factors; D011993:Recombinant Fusion Proteins; C553927:RopGEF1 protein, Arabidopsis; D010834:Phytochrome; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate