Regulation of the actin cytoskeleton by ROPs in plants

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Guanine nucleotide binding proteins of the Ras superfamily are involved in many signal transduction and transport processes. The subfamily of Rho proteins regulates reorganization of the actin cytoskeleton in many different biological systems. These pathways and mechanisms have been intensively studied in mammalian and yeast cells. It has been shown that Rho proteins act by binding to effectors, which are defined as proteins binding to the activated (GTP-bound) state of the GNBP. These effectors mediate the signal transduction cascade of Rho proteins by directly interacting with or regulating the activity of components of the actin treadmilling system. Rho homologous proteins (Rops) have been identified in plants (11 in Arabidopsis thaliana) but almost nothing is known of their regulation by GEFs and GAPs. Even less is known about the regulation of the actin cytoskeleton in plants since no homologues of the common effectors have so far been isolated from plants. Here we intend to clone, characterize and analyse biochemically and structurally the pathway leading from activation of Rops to its regulation of the actin cytoskeleton.