Heat shock effects on second messenger systems of Neurospora crassa

Abstract

Exposure of growing hyphae of Neurospora crassa to heat shock (44 degrees C) or ethanol (2.6 M) for 1 h induced a significant increase in the cAMP level, which reached a maximum approximately 2 min after the beginning of treatment and then decreased to control values despite continued heat or ethanol exposure. A 10-s heat shock or a 5-s ethanol shock also resulted in a transient cAMP increase 2 min after the pulse. Heat shock or ethanol treatment led to an increase in the amount of catalytic subunits of the cAMP-dependent protein kinase A in the nucleus almost synchronously with the increase of cAMP in the cytoplasm. The concentration of cGMP decreased a few seconds after the beginning of heat shock (44 degrees C) or ethanol treatment (2.6 M) to approximately 50% of the control level. Exposure to heat shock (44 degrees C, 1 h) led to an increase in the amount of inositol phosphates 0.5-2 min after the onset of heat shock. Thereafter, inositol phosphate levels dropped to control values despite continued heat exposure. Incubation of growing hyphae with cAMP or 8-Br-cAMP led to a two- to threefold increase of inositol phosphates 10-300 s after the beginning of incubation. Heat treatment furthermore caused a rapid release of calcium from vacuoles as determined by Fura-2 measurement of the calcium content released from isolated vacuoles. These heat-shock-dependent second messenger changes may play a role in the heat-shock-induced phase shifts of the circadian clock and heat-shock-induced conidiation.

An IP3-activated Ca2+ channel regulates fungal tip growth

“…The vacuolar IP3-activated Ca 2+ channel may be important in signaling during environmental stress. Heat shock causes rapid increases in intracellular second Journal of Cell Science 115 (24) messengers, cAMP and inositol phosphates (fivefold), as well as Ca 2+ release from isolated N. crassa vacuoles (Kallies et al, 1998). In addition, vacuoles may regulate the homeostasis of cytosolic Ca 2+ providing a storage reserve or detoxification system to prevent the effects of excessive Ca 2+ in the cytoplasm.…”

“…They failed to demonstrate stimulation of phosphoinositide turnover by a variety of external stimuli. However, Kallies (Kallies et al, 1998) found that normal IP3 concentration within growing hyphae of N. crassa increased two to fivefold to trigger Ca 2+ release during the heat shock response. IP3 signaling may be involved in the regulation of endogenous metabolism and differentiation since inhibitors of phosphoinositide turnover led to lower extension rates and increased hyphal branching (Hosking et al, 1995), including Li + inhibition of inositol metabolism and hyphal growth (Hanson, 1991).…”

Specific domains of plant defensins differentially disrupt colony initiation, cell fusion and calcium homeostasis in Neurospora crassa

“…Calcium plays a major role as a second messenger and transduces a wide range of chemical and physical signals through different intracellular signalling pathways, culminating in a variety of cellular responses (Berridge et al, 2003). In filamentous fungi, Ca 2+ signalling has been implicated in regulating many physiological processes including the cell cycle, spore germination, hyphal tip growth, hyphal orientation, hyphal branching, sporulation and circadian rhythms, as well as responses to osmotic stress, mechanical stimuli, heat shock, oxidative stress and electrical fields (Kallies et al, 1998;Cruz et al, 2001;Shaw and Hoch, 2001;Yang et al, 2001;Green et al, 2002;Joseph and Means, 2002;Nelson et al, 2004;Steinbach et al, 2006;Brand et al, 2007;Kim et al, 2012).…”