Phosphatidylinositol phosphates are important regulators of processes such as the cytoskeleton organization, membrane trafficking and gene transcription, which are all crucial for polarized cell growth. In particular, phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] has essential roles in polarized growth as well as in cellular responses to stress. In the yeast Saccharomyces cerevisiae, the sole phosphatidylinositol-4-phosphate 5-kinase (PI4P5K) Mss4p is essential for generating plasma membrane PtdIns(4,5)P2. Here, we show that Mss4p is required for yeast invasive growth in low-nutrient conditions. We isolated specific mss4 mutants that were defective in cell elongation, induction of the Flo11p flocculin, adhesion and cell wall integrity. We show that mss4-f12 cells have reduced plasma membrane PtdIns(4,5)P2 levels as well as a defect in its polarized distribution, yet Mss4-f12p is catalytically active in vitro. In addition, the Mss4-f12 protein was defective in localizing to the plasma membrane. Furthermore, addition of cAMP, but not an activated MAPKKK allele, partially restored the invasive growth defect of mss4-f12 cells. Taken together, our results indicate that plasma membrane PtdIns(4,5)P2 is crucial for yeast invasive growth and suggest that this phospholipid functions upstream of the cAMP-dependent protein kinase A signaling pathway.
Keywords: Invasive growth; PI4P5K; Phospholipids; Polarized growth; PtdIns(4,5)P2; Yeast.