Van de Velde Sam, Thevelein Johan M
Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, and Department ofMolecular Microbiology, VIB, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium.
Eukaryot Cell. 2008 Feb;7(2):286-93. doi: 10.1128/EC.00276-07. Epub 2007 Sep 21.
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 mitogen-activated protein kinase, cyclic AMP-protein kinase A (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 mep2Delta/mep2Delta 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 G-protein-coupled receptor Gpr1, whereas it 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 gene 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.
在特定环境条件下，酿酒酵母可经历形态转变，形成假菌丝生长模式。假菌丝分化通常在葡萄糖存在下通过氮限制诱导进行研究。已知其受多种信号通路控制，包括丝裂原活化蛋白激酶、环磷酸腺苷 - 蛋白激酶A（cAMP - PKA）和Snf1激酶通路。我们发现，α - 葡糖苷糖麦芽糖和麦芽三糖，尤其是蔗糖，比葡萄糖更能有效诱导丝状化。蔗糖甚至能在富氮培养基中以及在铵限制培养基上的mep2Delta/mep2Delta铵通透酶突变体中诱导丝状化。我们证明，葡萄糖还通过一条与cAMP - PKA通路平行的途径抑制丝状化。HXK2基因的缺失将葡萄糖上的假菌丝生长模式转变为蔗糖上的模式，而SNF4基因的缺失则消除了两种糖上的丝状化，表明葡萄糖阻遏起负作用，而Snf1活性在丝状化控制中起正作用。在所有菌株和所有培养基中，蔗糖诱导的丝状化因蔗糖/葡萄糖传感G蛋白偶联受体Gpr1的缺失而大大减弱，而对麦芽糖和麦芽三糖诱导无影响。α - 葡糖苷糖诱导丝状化的能力反映在细胞表面絮凝蛋白基因FLO11表达的增加上。此外，蔗糖是唯一能够以Gpr1依赖方式快速诱导FLO11表达的α - 葡糖苷糖，这反映了Gpr1对这种糖的敏感性及其参与快速蔗糖信号传导。我们的研究确定蔗糖是假菌丝生长最有效的营养诱导物，并表明Snf1激酶信号传导的葡萄糖失活是葡萄糖效力较低的原因。
