Regulatory interaction of PRL1 WD protein with Arabidopsis SNF1-like protein kinases

Mutation of the PRL1 gene, encoding a regulatory WD protein, results in glu cose hypersensitivity and derepression of glucose-regulated genes in Arabid opsis, The yeast SNF1 protein kinase, a key regulator of glucose signaling, and Arabidopsis SNF1 homologs AKIN10 and AKIN11, which can complement the Delta snf1 mutation, were found to interact with an N-terminal domain of th e PRL1 protein in the two-hybrid system and in vitro. AKIN10 and AKIN11 sup press the yeast Delta snf4 mutation and interact with the SNF4p-activating subunit of SNF1. PRL1 and SNF4 bind independently to adjacent C-terminal do mains of AKTN10 and AKIN11, and these protein interactions are negatively r egulated by glucose in yeast. AKIN10 and AKIN11, purified in fusion with gl utathione S-transferase, undergo autophosphorylation and phosphorylate a pe ptide of sucrose phosphate synthase in vitro, The sucrose phosphate synthas e-peptide kinase activity of AKIN complexes detected by immunoprecipitation is stimulated by sucrose in light-grown Arabidopsis plants, In comparison with wild type, the activation level of AKIN immunocomplexes is higher in t he prl1 mutant, suggesting that PRL1 is a negative regulator of Arabidopsis SNF1 homologs, This conclusion is supported by the observation that PRL1 i s an inhibitor of AKIN10 and AKIN11 in vitro.