2.5.1.85 fibrillin 5B FBN5-B, fibrillin 5B specifically interacts with solanesyl diphosphate synthase 1, which biosynthesize the solanesyl moiety of plastoquinone-9. Plants containing defective FBN5-B accumulate less plastoquinone-9 and its cyclized product, plastochromanol-8, but the levels of tocopherols are not affected. Homozygous mutations in FBN5 are seedling-lethal. FBN5-B is required for PQ-9 biosynthesis through its interaction with enzyme SPS. FBN5 binding to the hydrophobic solanesyl moiety, which is generated by SPS1, in FBN5 B/SPS homodimeric complexes stimulates the enzyme activity of SPS1 739297 2.5.1.85 fibrillin 5B FBN5-B, fibrillin 5B specifically interacts with solanesyl diphosphate synthase 2, which biosynthesize the solanesyl moiety of plastoquinone-9. Plants containing defective FBN5-B accumulate less plastoquinone-9 and its cyclized product, plastochromanol-8, but the levels of tocopherols are not affected. Homozygous mutations in FBN5 are seedling-lethal. FBN5-B is required for PQ-9 biosynthesis through its interaction with enzyme SPS. FBN5 binding to the hydrophobic solanesyl moiety, which is generated by SPS2, in FBN5 B/SPS homodimeric complexes stimulates the enzyme activity of SPS2 739297