UV-B perception by the photoreceptor UVR8 initiates a signaling cascade that leads to UV-B acclimation. Several components of the UV-B signaling pathway have been identified and characterized in the last decade and significant insight into the perception mechanism was obtained. However, our understanding on how UV-B photoreception by UVR8 leads to transcriptional changes is far from being coherent and complete. UV-B signal transduction within the UV-B signaling pathway involves the interaction of photoactivated UVR8 with its signaling partner COP1 and an activity of the transcription factor HY5 at UV-B-responsive promoters. In this work I aimed to gain insight into the molecular events bridging the gap from UVR8-COP1 interaction to HY5-mediated UV-B-responsive gene expression. I addressed the following questions: 1) How does HY5 regulate gene expression in response to UV-B? 2) Is there a function of UVR8 at the chromatin level? 3) What other proteins are regulating UVR8-COP1-mediated UV-B signaling pathway?