4 ジャガイモ夏疫病菌Alternaria solaniのsolanapyrone生合成遺伝子クラスター(口頭発表の部)

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Alternaria solani, a causal fungus of potato early blight disease, produces phytotoxic reduced-type polyketides such as solanapyrones and alternaric acid. In the course of our study on fungal polyketide synthases (PKSs), solanapyrone biosynthetic gene cluster was identified in A. solani. Four new PKS gene fragments were amplified from A. solani genomic DNA. Sequences of entire PKS genes and surrounding regions were determined by PCR-based gene walking method. One of the gene clusters contained a gene for a typical iterative type I PKS with C-methyltransferase domain which is necessary for the prosolanapyrone synthesis and five genes for O-methyltransferase, dehydrogenase, transcription factor, FAD-dependent oxidase, and cytochrome P450. These genes were considered to be just enough for solanapyrone biosynthesis, and thus named soil 〜6. The Soil PKS was expressed in Aspergilhts oryzae and its product was identified to be a solanapyrone precursor. desmethylprosolanapyrone I (5). Expression of Sol5 in A. oryzae confirmed its solanapyrone synthase activity to convert prosolanapyrone II (7) to solanapyrone A (1) by oxidation and Diels-Alder cyclization. The purified enzyme from the recombinant Pichia pastoris showed the same stereo-specificity in conversion of (7) to (1) as the native solanapyrone synthase does.
2007-08-24