Determines thylakoid architecture by inducing membrane curvature. Homo- and heterodimers and trimers. No effect on growth behavior, leaf coloration, grana stacks or photochemical efficiency of photosystem II. Curt1a, curt1b, curt1c and curt1d quadruple mutant shows disorganized thylakoids with extended stretches of unstacked membranes and broader stacks made up of fewer layers. Belongs to the CURT family.