Light and gibberellins (GAs) regulate essential plant developmental processes, including hypocotyl elongation, cotyledon opening, and light-responsive gene expression in Arabidopsis thaliana. DELLA proteins, which are GA-signaling repressors, accumulate in the absence of GA and inhibit the activity of the light-responsive transcription factor PIF3, thereby suppressing light-induced hypocotyl elongation. In the presence of GA, GID1 proteins (GA receptors) interact with DELLA proteins in the nucleus, leading to their ubiquitination and proteasome-mediated degradation, which releases PIF3 and allows it to regulate gene expression. This interaction is crucial for the coordination of GA and light signaling in plant development. The study shows that DELLA proteins are under negative control by GA and the proteasome. When GA is present, DELLA proteins are degraded, releasing PIF3 and allowing it to promote hypocotyl elongation in light. Conversely, in the absence of GA, DELLA proteins accumulate and inhibit PIF3, preventing hypocotyl elongation. The interaction between DELLA proteins and PIF3 is regulated by GA and light, with GA promoting the degradation of DELLA proteins and thus releasing PIF3. This interaction is essential for the coordinated control of hypocotyl growth by light and GA. The study also demonstrates that DELLA proteins inhibit PIF3 function by protein-protein interaction and sequestration, which at least partly explains their effect on gene expression and the coordinated control of hypocotyl growth by light and GA. The results support a model where GA signaling is initiated when GA molecules, whose biosynthesis is induced by light, are sensed and bound by nuclear GID1 proteins. This leads to the degradation of DELLA proteins, releasing PIF3 and allowing it to regulate gene expression. PIF3 belongs to a transcription factor family defined by a conserved bHLH domain, which is involved in DNA binding and dimerization. DELLA proteins also interact with the DNA-binding bHLH domain of PIF3, consistent with the observation that RGA–PIF3 and PIF3–promoter interactions are mutually exclusive. Through modulating multiple phytochrome-interacting transcription factors, DELLA proteins play a key part in integrating the regulatory effect of light and GA on gene expression and plant development. The study provides a detailed understanding of the molecular mechanisms underlying the coordination of GA and light signaling in Arabidopsis thaliana.Light and gibberellins (GAs) regulate essential plant developmental processes, including hypocotyl elongation, cotyledon opening, and light-responsive gene expression in Arabidopsis thaliana. DELLA proteins, which are GA-signaling repressors, accumulate in the absence of GA and inhibit the activity of the light-responsive transcription factor PIF3, thereby suppressing light-induced hypocotyl elongation. In the presence of GA, GID1 proteins (GA receptors) interact with DELLA proteins in the nucleus, leading to their ubiquitination and proteasome-mediated degradation, which releases PIF3 and allows it to regulate gene expression. This interaction is crucial for the coordination of GA and light signaling in plant development. The study shows that DELLA proteins are under negative control by GA and the proteasome. When GA is present, DELLA proteins are degraded, releasing PIF3 and allowing it to promote hypocotyl elongation in light. Conversely, in the absence of GA, DELLA proteins accumulate and inhibit PIF3, preventing hypocotyl elongation. The interaction between DELLA proteins and PIF3 is regulated by GA and light, with GA promoting the degradation of DELLA proteins and thus releasing PIF3. This interaction is essential for the coordinated control of hypocotyl growth by light and GA. The study also demonstrates that DELLA proteins inhibit PIF3 function by protein-protein interaction and sequestration, which at least partly explains their effect on gene expression and the coordinated control of hypocotyl growth by light and GA. The results support a model where GA signaling is initiated when GA molecules, whose biosynthesis is induced by light, are sensed and bound by nuclear GID1 proteins. This leads to the degradation of DELLA proteins, releasing PIF3 and allowing it to regulate gene expression. PIF3 belongs to a transcription factor family defined by a conserved bHLH domain, which is involved in DNA binding and dimerization. DELLA proteins also interact with the DNA-binding bHLH domain of PIF3, consistent with the observation that RGA–PIF3 and PIF3–promoter interactions are mutually exclusive. Through modulating multiple phytochrome-interacting transcription factors, DELLA proteins play a key part in integrating the regulatory effect of light and GA on gene expression and plant development. The study provides a detailed understanding of the molecular mechanisms underlying the coordination of GA and light signaling in Arabidopsis thaliana.