Fundamental contribution of beta-oxidation to polyketide mycotoxin production in planta.
Seed contamination with polyketide mycotoxins, including aflatoxin (AF) and sterigmatocystin (ST) produced by Aspergillus spp., is an agricultural, economic, and medical issue worldwide. Acetyl-CoA, the fundamental building block of all known fungal polyketides, is generated by a large number of biochemical pathways, including beta-oxidation of fatty acids and glycolysis of sugars. We present several lines of evidence to support a major role for seed fatty acids in formation of AF and ST in A. flavus, A. parasiticus, and A. nidulans. Aspergillus strains exhibiting canonical signs of oleic acid-induced peroxisome proliferation, including increased catalase activity, beta-oxidation gene expression, and peroxisomal clustering, also exhibited a marked increase in toxin gene expression and biosynthesis. Furthermore, microscopic observations showed that the ST and AF precursor norsolorinic acid accumulated in peroxisomes of all three Aspergilli. While a peroxisomal beta-oxidation mutation eliminated oleic acid-induced increases in ST in A. nidulans, a mitochondrial beta-oxidation mutation played a larger role in eliminating ST formation on oatmeal medium and on live corn kernels, implicating a fundamental role for both peroxisomal and mitochondrial beta-oxidation in toxin production.
Maggio-Hall
Lori A
LA
Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706, USA.
Wilson
Richard A
RA
Keller
Nancy P
NP
D000348:Aflatoxins / Q000096:biosynthesis*; D000880:Anthraquinones / Q000378:metabolism; D001230:Aspergillus / Q000166:cytology / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D008928:Mitochondria / Q000378:metabolism; D009154:Mutation; D010084:Oxidation-Reduction; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics / Q000378:metabolism; D020675:Peroxisomes / Q000378:metabolism; D010944:Plants / Q000378:metabolism* / Q000382:microbiology*; D013241:Sterigmatocystin / Q000096:biosynthesis*; D014158:Transcription, Genetic
D000348:Aflatoxins; D000880:Anthraquinones; D005227:Fatty Acids; D013241:Sterigmatocystin; D044943:Fatty Acid Desaturases; C021904:Phosphatidylcholine desaturase; D044925:Oxidoreductases Acting on CH-CH Group Donors; C002754:norsolorinic acid