Alem, A. L.; Arce, A. L.; Blanchard, C.; Gomez, M. D.; Carrera, E.; Lamotte, O.; Perez-Amador, M. A.; Capella, M.

Photomorphogenesis allows plants to adjust growth to ambient light conditions and relies on protein quality control to ensure the timely turnover of signaling components. The conserved AAA+ ATPase CDC48, along with its cofactors NPL4 and UFD1, is a crucial regulator of proteasomal degradation. While well characterized in other organisms, its role in plant development remains largely unexplored. Here, we show that CDC48 is required for blue light-mediated photomorphogenesis in Arabidopsis. Under blue light, CDC48A accumulates at the plasma membrane and in the nucleus, and cdc48a mutants fail to repress hypocotyl elongation properly. Similar phenotypes are observed upon inhibition of CDC48 or in npl4 and ufd1 mutants. Genetic and biochemical analyses further reveal that CDC48A negatively regulates gibberellin (GA) signaling. Consistently, UFD1 directly interacts with the GA receptor GID1 to promote its degradation. Together, these findings demonstrate that CDC48A integrates light and hormonal cues through protein homeostasis to regulate photomorphogenic development.