Required for brassinosteroid- (BR) mediated post-transcriptional and translational regulation in the chloroplast, including accumulation of chloroplast rRNA (PubMed:19919572). Involved in chloroplast differentiation (PubMed:19919572, PubMed:22526496). Binds to chloroplast 16S and 23S ribosomal RNAs. Mostly expressed in stems, petioles, leaves and flowers and, at low levels, also in roots. Induced by light, but repressed by dark (PubMed:19919572, PubMed:22526496). Up-regulated by the specific inhibitor of the biosynthesis of brassinosteroids (BRs) brassinazole (Brz) (PubMed:19919572). Chlorotic dwarf mutant pale green in bpg2-1 and bpg2-2 (PubMed:19919572, PubMed:19889879, PubMed:22526496). Reduced sensitivity in the light to chlorophyll accumulation promoted by brassinazole (Brz), a specific inhibitor of the biosynthesis of brassinosteroids (BRs), via the suppression of Brz-induced chloroplast protein accumulation. Decreased number of stacked grana thylakoids in chloroplast, but more starch grains, and more and larger plastoglobules. Abnormal accumulation of precursors of chloroplast 16S and 23S rRNA (PubMed:19919572). Reduced level of chlorophyll and carotenoid pigmentation in plastids leading to defective photosystem II and altered photosystem I functions (PubMed:22526496). Belongs to the TRAFAC class YlqF/YawG GTPase family.