The G protein-coupled receptor Gpr1 is a nutrient sensor that regulates pseudohyphal differentiation in Saccharomyces cerevisiae

Pseudohyphal differentiation in the budding yeast Saccharomyces cerevisiae is induced in diploid cells in response to nitrogen starvation and abundant fermentable carbon source. Filamentous growth requires at least two signal ing pathways: the pheromone responsive MAP kinase cascade and the Gpa2p-cAM P-PKA signaling pathway. Recent studies have established a physical and fun ctional link between the G alpha protein Gpa2 and the G protein-coupled rec eptor homolog Gpr1. We report here that the Gpr1 receptor is required for f ilamentous and haploid invasive growth and regulates expression of the cell surface flocculin Flo11. Epistasis analysis supports a model in which the Gpr1 receptor regulates pseudohyphal growth via the Gpa2p-cAMP-PKA pathway and independently of both the MAP kinase cascade and the PKA related kinase Sch9. Genetic and physiological studies indicate that die Gpr1 receptor is activated by glucose and other structurally related sugars. Because expres sion of the GPR1 gene is known to be induced by nitrogen starvation, the Gp r1 receptor may serve as a dual sensor of abundant carbon source (sugar lig and) and nitrogen starvation. In summary, our studies reveal a novel G prot ein-coupled receptor senses nutrients and regulates the dimorphic transitio n to filamentous growth via a G alpha protein-cAMP-PKA signal transduction cascade.