LAUSR

Abstract Scaffold proteins regulate cellular mechanisms and phenotypic patterns through protein-to-protein interactions. Receptor for Activated C Kinase 1 (RACK1) is a highly conserved protein containing 40 amino acid repeats of tryptophan-aspartic acid dipeptides (WD-repeat). RACK1 regulates environmental stress signaling pathways in plants and has important implications for human diseases (e.g., viral infections, cancer) and organ function (e.g., brain, heart, liver). Three isoforms (RACK1A, RACK1B and RACK1C) in plants are associated with drought, salt uptake, UV and oxidative stress. We characterized the regulatory role of RACK1 in Arabidopsis thaliana and Oryza sativa using gain of function mutants by T-DNA insertion. Wild type A. thaliana normally displays RACK1 promoter activity (GUS staining) only in leaf tips, but GUS staining after oxidative stress (methyl viologen) was dispersed throughout the leaf and elevated in stomata. Overexpression of RACK1 causes a stressed phenotype and retarded growth in heterozygous O. sativa mutants, while a severely stressed phenotype and failure to thrive (within two weeks of germination) was observed in homozygous mutants. Methyl viologen exposure of leaves in RACK1 gain of function O. sativa decreased chlorophyll content and increased reactive oxygen species. Our findings support previous studies indicating that RACK1 regulates ROS production in O. sativa seedlings. Our results provide important baseline data for future fine-scale characterizations of important developmental regulators imposed by the modulation of RACK1 (and other isoforms). Understanding plant-based food security and human disease pathologies (including viral infections) will inform strategies that aim to reduce the negative impacts of each process to sustain society worldwide.