cAMP-PKA and Snf1 signaling mechanisms underlie the superior potency of sucrose for induction of filamentation in yeast

Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium

^* To whom correspondence should be addressed. Email: johan.thevelein{at}bio.kuleuven.be.

	Abstract

Under specific environmental conditions, the yeast Saccharomyces cerevisiae can undergo a morphological switch to a pseudohyphal growth pattern. Pseudohyphal differentiation is generally studied upon induction by nitrogen limitation in the presence of glucose. It is known to be controlled by several signaling pathways, including MAP kinase, cAMP-PKA and Snf1 kinase pathways. We show that the alpha-glucoside sugars maltose and maltotriose and especially sucrose are more potent inducers of filamentation than glucose. Sucrose even induces filamentation in nitrogen-rich media and in the mep2/mep2 ammonium permease mutant on ammonium-limiting medium. We demonstrate that glucose also inhibits filamentation by means of a pathway parallel to the cAMP-PKA pathway. Deletion of HXK2 shifted the pseudohyphal growth pattern on glucose to that of sucrose, while deletion of SNF4 abrogated filamentation on both sugars, indicating a negative role of glucose repression and a positive role for Snf1 activity in the control of filamentation. In all strains and in all media, sucrose induction of filamentation is greatly diminished by deletion of the sucrose/glucose sensing GPCR Gpr1 whereas this has no effect on induction by maltose and maltotriose. The competence of alpha-glucoside sugars to induce filamentation is reflected in the increased expression of the cell surface flocculin FLO11. In addition, sucrose is the only alpha-glucoside sugar capable of rapidly inducing FLO11 expression in a Gpr1-dependent manner, reflecting the sensitivity of Gpr1 for this sugar and its involvement in rapid sucrose signaling. Our study identifies sucrose as the most potent nutrient inducer of pseudohyphal growth and shows that glucose inactivation of Snf1 kinase signaling is responsible for the lower potency of glucose.