The article explores the molecular framework for the control of cell elongation in seedlings by light and gibberellins (GAs). Light inhibits hypocotyl growth, promoting cotyledon opening and chloroplast differentiation, while GAs promote etiolated growth. The central role of the *Arabidopsis thaliana* nuclear transcription factor PIF4 in the positive control of genes mediating cell elongation is highlighted. PIF4 is negatively regulated by the light photoreceptor phyB and by DELLA proteins, which are key repressors in GA signaling. The study demonstrates that PIF4 is destabilized by phyB in the light and that DELLA proteins block PIF4 transcriptional activity by binding to its DNA-recognition domain. GAs abrogate this repression by promoting DELLA destabilization, leading to the accumulation of free PIF4 in the nucleus. Intermediate hypocotyl lengths are observed in transgenic plants over-accumulating both DELLA and PIF4. The interaction between phyB and DELLA proteins explains how plants integrate light and GA signals to optimize growth and development in response to changing environments.The article explores the molecular framework for the control of cell elongation in seedlings by light and gibberellins (GAs). Light inhibits hypocotyl growth, promoting cotyledon opening and chloroplast differentiation, while GAs promote etiolated growth. The central role of the *Arabidopsis thaliana* nuclear transcription factor PIF4 in the positive control of genes mediating cell elongation is highlighted. PIF4 is negatively regulated by the light photoreceptor phyB and by DELLA proteins, which are key repressors in GA signaling. The study demonstrates that PIF4 is destabilized by phyB in the light and that DELLA proteins block PIF4 transcriptional activity by binding to its DNA-recognition domain. GAs abrogate this repression by promoting DELLA destabilization, leading to the accumulation of free PIF4 in the nucleus. Intermediate hypocotyl lengths are observed in transgenic plants over-accumulating both DELLA and PIF4. The interaction between phyB and DELLA proteins explains how plants integrate light and GA signals to optimize growth and development in response to changing environments.