Blue light adaptation and desensitization of light signal transduction in Neurospora crassa

The ascomycete Neurospora crassa has the capacity of adapting to a given li ght quantity, leading to transient blue light responses under continuous li ght conditions. Here, we present an investigation of this photoadaptation p henomenon. We demonstrated previously that two proteins of the Neurospora b lue light signal transduction chain, WC1 and WC2, are subject to light-depe ndent phosphorylation. WC1 was phosphorylated in parallel with the transien t increase in transcript levels of light-regulated genes. Using the light-d ependent phosphorylation of WC1 as a marker for an active signalling state of WC1, we show that the transiency of Neurospora blue light responses resu lts from desensitization of the photoreceptor and/or the signalling cascade . Furthermore, a Neurospora mutant was characterized that revealed a specif ic defect in photoadaptation. In this mutant, the transient expression of l ight-regulated genes under continuous light, the temporary insensitivity af ter a light pulse and the capability of differentiating between and adaptin g to low and high light intensities were abolished. The corresponding prote in seems to represent a central component of a negative feedback desensitiz ation mechanism. This negative feedback regulation requires continuous and light-dependent protein de novo biosynthesis.