Chapter 14 : Sensing Extracellular Signals in

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The chapter describes the abilities of to sense and adapt to a subset of environmental conditions it encounters. The mechanisms for sensing extracellular signals such as stress, light, nitrogen, carbon dioxide, and oxygen are emerging. There are several future paths toward understanding the light responses of . First, the functions of the opsin and phytochrome in light sensing, if any, are currently unknown. Second, the conformational effects of light on the white collar complex are also unknown in or in detail from any fungal system since the proteins are notoriously difficult to purify in abundance for structural and other studies. Third, the genes that are regulated by light remain to be fully elucidated, although this is being addressed through transcript profiling microarray and genetic screens, particularly since these genes should control ability to proliferate in the wild and cause disease in humans. The current model of the CO-sensing system in suggests that under limiting concentrations this molecule diffuses into the cell and is subsequently hydrated to HCO and fixed inside the cell by the CA Can2p. Analysis of deletion mutants identified two genes in addition to and that were required for full growth under hypoxic conditions. It is of interest to note that mutation of SRE1 and SCP1 leads to an increased sensitivity to ROS, which led Ingavale et al. to propose that there is a link in oxygen sensing between hypoxia, mitochondrial function, and ROS generation.

Citation: Idnurm A, Bahn Y, Shen W, Rutherford J, Mühlschlegel F. 2011. Sensing Extracellular Signals in , p 175-187. In Heitman J, Kozel T, Kwon-Chung K, Perfect J, Casadevall A (ed), . ASM Press, Washington, DC. doi: 10.1128/9781555816858.ch14
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Image of FIGURE 1

Stress-sensing pathways of . Extracellular stresses are sensed and the signal transmitted via signaling pathways. At present only a handful of regulators with overlapping functions are known that enter, or are predicted to enter, the nucleus to alter transcription.

Citation: Idnurm A, Bahn Y, Shen W, Rutherford J, Mühlschlegel F. 2011. Sensing Extracellular Signals in , p 175-187. In Heitman J, Kozel T, Kwon-Chung K, Perfect J, Casadevall A (ed), . ASM Press, Washington, DC. doi: 10.1128/9781555816858.ch14
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Image of FIGURE 2

Light sensing is mediated by homologs of white collar 1 and 2 to control at least three responses in . Deletion of either the or gene renders insensitive to the inhibition of mating by light, increases UV sensitivity, and reduces virulence. (A) Strains of both mating types were cocultured in the light or dark for 2 days at room temperature on Murashige-Skoog medium. (B) Tenfold serial dilutions of wild-type and mutant strains were made on yeast extract peptone dextrose medium, and one set was irradiated with UV (100 J/m). Plates were incubated for 2 days at 30°C. (C) Ten mice were infected with strains, and survival was monitored over time. Data from Idnurm and Heitman ( ).

Citation: Idnurm A, Bahn Y, Shen W, Rutherford J, Mühlschlegel F. 2011. Sensing Extracellular Signals in , p 175-187. In Heitman J, Kozel T, Kwon-Chung K, Perfect J, Casadevall A (ed), . ASM Press, Washington, DC. doi: 10.1128/9781555816858.ch14
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Image of FIGURE 3

Carbon dioxide sensing in . CO affects both capsule biosynthesis and mating. Carbon dioxide diffuses into the cell and is either spontaneously hydrated (elevated environmental concentrations of CO) to bicarbonate or alternatively enzymatically hydrated (low environmental concentrations of CO) by the action of the CA Can2. Bicarbonate stimulates the AC Cac1.

Citation: Idnurm A, Bahn Y, Shen W, Rutherford J, Mühlschlegel F. 2011. Sensing Extracellular Signals in , p 175-187. In Heitman J, Kozel T, Kwon-Chung K, Perfect J, Casadevall A (ed), . ASM Press, Washington, DC. doi: 10.1128/9781555816858.ch14
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Image of FIGURE 4

The fungal AC is a multidomain sensor. Serum, CO, and the quorum sensing molecules farnesol and 3-oxy-C12-homoserine lactone (3OC12HSL) influence AC activity in the fungal pathogen .

Citation: Idnurm A, Bahn Y, Shen W, Rutherford J, Mühlschlegel F. 2011. Sensing Extracellular Signals in , p 175-187. In Heitman J, Kozel T, Kwon-Chung K, Perfect J, Casadevall A (ed), . ASM Press, Washington, DC. doi: 10.1128/9781555816858.ch14
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