ON THE COVER

Using a range of approaches, Schreier et al. (pages 1745–1769) show that the plastid-localized malate dehydrogenase pdNAD-MDH is needed for the proper development of chloroplasts during embryogenesis. Surprisingly, the authors found that the enzymatic activity of pdNAD-MDH is not required in these processes, but only the pdNAD-MDH protein itself. They show that the pdNAD-MDH protein appears to have a second, “moonlighting” function, distinct from its enzymatic activity, that functions in stabilizing the FtsH12 complex at the chloroplast inner envelope membrane. The cover image shows a close-up photograph of the meristematic zone of a 4-week-old Arabidopsis pdnad-mdh mutant, rescued by the expression of plastidial NAD-dependent malate dehydrogenase (pdNAD-MDH) exclusively during embryo development (pdnad-mdh knockout mutants are otherwise embryo-lethal).