| WC-1 and WC-2 are essential for most light responses in Neurospora crassa, but the molecular mechanisms underlying gene induction and the roles of other real and putative photoreceptors remain poorly characterized. Unsupervised hierarchical clustering of genome-wide microarrays reveals 5.6% of detectable transcripts, including several novel mediators, that are either early or late light-responsive. White Collar Complex (WCC) regulates both types of light responses. Light-responsive Submerged Protoperithecia-1 (SUB-1), a GATA family transcription factor, is essential for most late light responses. Following a 15-minute light stimulus, the WCC directly binds the sub-1 promoter. Bioinformatics analysis detects many Early Light Response Elements (ELREs), as well as Late Light Response Elements (LLREs). These data provide a global picture of the transcriptional response to light, as well as illuminating the cis and trans-acting elements comprising the regulatory signaling cascade that governs the photobiological response.;Photoadaptation, the ability to attenuate a light response upon prolonged light exposure while remaining sensitive to escalating changes in light intensity, is essential for organisms to appropriately decipher time information, yet the underlying molecular mechanisms are poorly understood. In Neurospora crassa, VVD, a small LOV domain containing photoreceptor protein, is responsible for most photoadaptation responses. We report that there is a physical interaction between VVD and the WCC. Using two previously characterized VVD mutants, we show that the level of interaction is correlated with the level of WCC repression in constant light, and that even light-insensitive VVD is sufficient to regulate photoadaptation in vivo. We provide evidence that a functional GFP-VVD fusion protein accumulates in the nucleus upon light induction but that nuclear localization of VVD does not require light. Constitutively expressed VVD alone is sufficient to change the dynamics of photoadaptation. Thus, our results demonstrate a direct molecular connection between two of the most essential light signaling components in Neurospora, VVD and WCC, illuminating a previously uncharacterized process for light-sensitive eukaryotic cells. |
