Involved in the stable assembly of several 4Fe-4S cluster-containing complexes of chloroplasts. May participate in 4Fe-4S cofactor incorporation into psaA and/or psaB during translation. A number of isoforms are produced. According to EST sequences. Expressed at low level. Expressed at higher level in leaves. Expressed at lower level in roots, stems, siliques and flowers. Up-regulated during photomorphogenesis. The APO repeats may provide ligands for 4Fe-4S centers. Plants fail to accumulate significant amounts of the outer antenna subunits of PSI and PSII and to form grana stacks. 2Fe-2S cluster-containing complexes appear to be unaffected. Belongs to the APO family.