Poster: Temperature responses
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P09014: Sumoylation of dimerized RACK1 scaffold protein regulates elevated temperature stress signal transduction pathways in Arabidopsis
WD-40 repeat containing RACK1 (Receptor for Activated C Kinase 1- 36kDa) scaffold protein in metazoan plays a major role in coordinating different signal transduction pathways. As opposed to single gene in non-plant kingdom, Arabidopsis maintains three essentially identical RACK1 genes. In addition to a conserved sumoylation site within the RACK1 proteins from all species, plant RACK1 proteins possess an additional sumoylation site within a plant-specific short C-terminal amino acid block. Sumoylation status regulates protein-protein interaction, targeting, and stability of substrates that in turn predominantly regulate cell signaling and gene expression processes. Using gene knock-out, here we show that Arabidopsis RACK1A gene regulates diverse environmental stress responses and sumoylation status of obligatively dimerized RACK1 proteins mediates elevated heat stress responses. In normal growth temperature, RACK1 potentially gets sumoylated in both sites; however, elevated temperature abolishes/reduces sumoylation from one of the potential sites implying a major site of regulation. Split-ubiquitin based proximity sensor assay conclusively revealed that all three Arabidopsis RACK1 proteins could interact with each other. Dimerization between different members of a protein family can generate considerable functional diversity when different protein combinations have distinct regulatory properties. Screening a split-ubiquitin ready library with RACK1A protein as bait identified intractors in stress pathways. The first report of RACK1 sumoylation should open up intense interest in reevaluation of the scaffold attributes of RACK1 proteins from both plants and animals.
