Chloroplast chaperone required for RuBisCo biogenesis and translational regulation of the RuBisCo large subunit (RbcL) (PubMed:29217567). Stabilizes an end-state assembly intermediate of eight RbcL subunits until the small subunits (RBCSs) become available to produce a complete stable RuBisCo complex containing eight small and eight large subunits (PubMed:29217567). Interacts with the RuBisCo large subunit (RbcL) assembled as an intermediate complex made of eight RbcL and eight BSD2 subunits. Associates with chloroplastic polysomes. Belongs to the BSD2 chaperone family.