Essential for plastoquinone-9 (PQ-9) biosynthesis (PubMed:26432861, PubMed:29741733). Interacts with the diphosphate synthases SPS1 and SPS2, and binds to the hydrophobic solanesyl moiety, which is generated by SPS1 and SPS2, in FBN5-SPS homodimeric complexes to stimulate the enzyme activity of SPS1 and SPS2 (PubMed:26432861). Interacts with SPS1 and SPS2. Expressed in developing roots, developing leaves, young stems and sepals. Seedling lethality (PubMed:26432861, PubMed:28751900). Severe reduced growth, strong reduction of levels of plastoquinone-9 (PQ-9), and loss of plastochromanol-8 (PC-8) in leaves when grown on MS medium supplemented with sucrose (PubMed:26432861, PubMed:28751900). Severe decrease of photosynthetic performance and higher levels of reactive oxygen species (ROS) under cold stress (PubMed:26432861, PubMed:29741733). Belongs to the PAP/fibrillin family.