Peroxisomes are involved in biotin biosynthesis in Aspergillus and Arabidopsis

Among the eukaryotes only plants and a number of fungi are able to synthesize biotin. Although initial events leading to the biosynthesisof biotinremain largely unknown, the final steps are known to occur in the mitochondria. Here we deleted the Aopex5 and Aopex7 genes encoding the receptors for peroxisomal targeting signalsPTS1 and PTS2, respectively, in the filamentous fungus Aspergillus oryzae. In addition to exhibiting defects in the peroxisomaltargeting of either PTS1 or PTS2 proteins, the deletion strains also displayed growth defects on minimal medium containing oleic acid as the sole carbon source. Unexpectedly, these peroxisomaltransport-deficient strains also exhibited growth defects on minimal medium containing glucose as the sole carbon source that were remediated by the addition of biotinand its precursors, including 7-keto-8-aminopelargonic acid (KAPA). Genome database searches in fungi and plants revealed that BioF protein/KAPA synthase, one of the biotinbiosynthetic enzymes, has a PTS1 sequence at the C terminus. Fungal ΔbioF strains expressing the fungal and plant BioF proteins lacking PTS1 still exhibited growth defects in the absence of biotin, indicating that peroxisomaltargeting of KAPA synthase is crucial for the biotin biosynthesis. Furthermore, in the plant Arabidopsis thaliana, AtBioF localized to the peroxisomesthrough recognition of its PTS1 sequence, suggesting involvement of peroxisomesin biotin biosynthesisin plants. Taken together we demonstrate a novel role for peroxisomesin biotin biosynthesisand suggest the presence of as yet unidentified peroxisomalproteins that function in the earlier steps of biotin biosynthesis.