The initiation and establishment of photosynthetic reactions and their regulation is essential for plantdevelopment and survival. These processes involve changes in protein content and composition,pigment accumulation and distribution, and restructuration of membrane systems within the plastids.Indeed, changes of membrane morphology play an important role during chloroplast biogenesis,development, and light acclimation. Nevertheless, the molecular players that regulate these structuraladjustments are still under debate. Previously, a protein family named Curvature Thylakoid 1 (CURT1)has been described. It comprises membrane-anchored proteins localized in the thylakoid membraneswithin the chloroplast, and CURT1 proteins have been proposed as key modulators of thylakoidmorphology by mediating membrane bending, and thus, grana height and grana diameter. However, thebiological contribution of these proteins during plant development remains unknown. In this work, thebiological function of CURT1 proteins during light acclimation and chloroplast biogenesis ischaracterized. Results show that CURT1 proteins contribute to plant fitness by mediating thylakoidplasticity under fluctuating light conditions. Further, they modulate the packing of internal membranesin chloroplast precursors, known as prolamellar bodies (PLBs), and thereby regulating chloroplastbiogenesis. Finally, CURT1 proteins are proposed as a versatile multi-organism tool for proteinscaffolding.