Sensing the environment: lessons from fungi

Key Points G-protein-coupled receptors (GPCRs) function as both pheromone and glucose sensors in fungi, whereas transceptors such as Snf3 and Rgt2 are involved in glucose sensing. Fungi have evolved sophisticated amino-acid-sensing systems including Ssy1–Ptr3–Ssy5 (SPS), Gap1 and GPCRs. The transceptors Pho84 and Pho87 have key roles in phosphate sensing. In eukaryotic organisms, the cyclic AMP–protein kinase A (cAMP–PKA) and TOR pathways transmit nutrient-derived signals to regulate a myriad of common targets that control complex translational and transcriptional programmes to coordinate nutrient availability with cell growth and differentiation. Fungi sense gases, such as CO 2 and ammonia, to control various cellular responses. Carbonic anhydrase maintains CO 2 /HCO 3 − homeostasis and thereby regulates the cAMP–PKA pathway, which in turn controls growth, differentiation and virulence factors of pathogenic fungi. Ammonia gas is an intercolony signalling mediator that has an important role in the growth and survival of multicellular yeast colonies. Opsins, phytochromes and white collar-1 proteins function in light sensing in fungi, with a conserved role for white collar proteins in blue-light sensing in diverse species. The downstream signalling events after light exposure are yet to be fully illuminated. Fungi use evolutionarily conserved signalling pathways, including the p38/Hog1 mitogen-activated protein kinase (MAPK) pathway and the nutrient sensing Tor and cAMP–PKA pathway, to confer cellular responses against various environmental stresses. However, the development of fungal-specific upstream and downstream systems is also evident, as exemplified by the multi-component phosphorelay system. For successful virulence, pathogenic fungi must counteract a plethora of host-specific factors, such as serum and immune cells in animals, and plant hormones, fatty acids and hard mechanical surface in plants. Signalling pathways that are responsible for the fungus–host interaction include the cAMP–PKA pathway and calcineurin pathway, however many aspects of fungal–host interactions remain to be elucidated. All organisms use numerous signal-transduction systems to sense and respond to their environments and survive in a range of biological niches. Here, the authors review the molecular mechanisms used by the fungal kingdom to sense, and adapt in response to, diverse environmental cues. All living organisms use numerous signal-transduction systems to sense and res