A small GTPase Activator Protein Interacts with cytoplasmic phytochromes in regulating root development.

Phytochromes enable plants to sense light information and regulate the developmental responses. Phytochromes interact with partner proteins to transmit light signals to downstream components for plant development. Phytochrome-interacting ROP (Rho-like GTPase of plant) guanine-nucleotide exchange factor (RopGEF11), PIRF1, functions as a light-signaling switch regulating root development through the activation of ...
ROPs in the cytoplasm. In vitro pull-down 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 (BiFC) analysis demonstrated that PIRF1 was localized in the cytoplasm and bound to the phytochromes in the darkness but not in the 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 signalings are interconnected through PIRF1 in regulating the root growth and development in Arabidopsis.
Mesh Terms:
Circadian Rhythm, Flowers, Gene Expression Profiling, Gene Expression Regulation, Developmental, Gene Expression Regulation, Plant, Immunoblotting, Oryza sativa, Photoperiod, Plant Proteins, RNA, Messenger
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Date: Jun. 15, 2010
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