9416027 Soll Gravity is one of the primary environmental signals determining the orientation of root and shoot growth in many plant species. The gravitropic response involves perception of the gravity signal, transmission of the signal, and execution of a response program that re-orients growth. Thus gravitropism constitutes a plant signal transduction pathway. This pathway is known to depend on tranport and reception of the plant hormone auxin. This research is designed to identify and characterize genes involved in the gravitropic response in Arabidopsis thaliana. Several mutants with defects in gravitropism have already been isolated. The focus here will be on the anlysis of two especially promising mutants, rgr1 and rcn1. The data indicates that the RCN1 gene encodes a phosphoprotein phosphatase, suggesting a specific role for RCN1 in gravitropic signal transduction; the role of RGR1 remains unknown. Work will continue on physiological and genetic characterization of the mutants, to establish the functions of the RGR1 and RCN1 genes. Molecular cloning and characterization of wild-type alleles will further define these roles. Wild-type clones will be re-introduced into Arabidopsis by Agrobacterium-mediated stable transformation to test for complementation of mutant phenotypes. Stable transformation experiemtns also will be used to demonstrate the biological effects of altering the normal expression pattersn of these genes. Genetic and molecular approaches will be used to elucidate interactions of the RGR1 and RCN1 genes with each other and with other genes involved in gravitropism. This work will provide new insights into the molecular mechanisms of gravitropism and of auxin-mediated signal transduction in plants. ***
