Final Activity Report Summary - DARK SIGNALING (Dark signaling mechanisms involved in the regulation of the developmental switch from dark to light growth in Arabidopsis seedlings) Historically, plant research has received less attention and funding than animal research, which has resulted in a lack of plant knowledge. Today, understanding how plants work is crucial if we want to solve pressing problems such as food shortages and climate change. Our step in increasing plant knowledge is to study the main plant decision-making headquarters: the plant cell nucleus. The nucleus is the place where important decisions affecting cell and ultimately plant growth are made. For example, after detecting environmental changes like drought or light stress, the nuclei will orchestrate the required response that will allow the plant to adapt. Our strategy is to break into the plant headquarters and reveal its governing members, who are now still largely unknown. In addition, we want to uncover how and when the members act, interact and discuss, and how the members organize themselves into committees where they make decisions and give the appropriate orders to the plant. This knowledge will be central to our success in improving our environment and food supply. The specific objective of this IRG project was to gain insight into the role of the bHLH-type transcription factor PIF3 (for phytochrome-interacting factor 3) as a plant growth regulator. PIF3 interacts with the activated form of the light photoreceptor phytochrome, and it is of critical importance in many aspects of light-regulated plant growth and development. However, its basic mechanism of action remains still largely unknown. Using a combination of (1) microarray analysis to analyse PIF3-regulated expression changes and (2) reverse genetics using mutants of the model plant Arabidopsis, we have identified several PIF3-regulated nuclear factors that are novel regulators of plant growth. This scientific achievement contributes to increase our understanding of how plants work, and further future characterisation of these novel factors will reveal their interactions and their role in the decision-making process of plants to regulate their responses to their environment.