6 Nutrient control of dimorphic growth in Saccharomyces cerevisiae

Abstract

In response to an abundant fermentable carbon source and limiting nitrogen, diploid yeast cells differentiate to form pseudohyphae that consist of chains of elongated cells. The G-protein coupled receptor Gpr1 senses extracellular glucose and signals via the coupled Gα subunit Gpa2. Gpa2 then stimulates cAMP production by adenylyl cyclase and activates the cAMP signaling pathway to promote pseudohyphal differentiation in diploid cells. Recently, the kelch repeat proteins Gpb1 and Gpb2 were identified as effectors and Gßsubunit mimics for Gpa2. The Gpr1- Gpa2-Gpb1/2-cAMP signaling cascade also controls a related cellular differentiation process, involving invasive growth that occurs in haploid cells grown on rich medium. Multiple signaling pathways function coordinately with the cAMP signaling pathway to govern both diploid pseudohyphal differentiation and haploid invasive growth. In this chapter, we review the current state of knowledge about the signaling cascades that sense nutrients and effect these alternative developmental cell fates.