Alternaria solani, a causal fungus of early blight disease to potato, produces reduced-type polyketides such as solanapyrone and alternaric acid. From this fungus, we cloned iterative type I polyketide synthase (iPKS) genes and related gene clusters. The alt gene cluster contains 5 genes alt1~5. Homology search indicated that the alt1, 2, and 3 code for cytochrome P450s and the alt4 for a FAD-dependent oxygenase/oxidase. The alt5 encodes an iPKS with a methyltransferase domain, named PKSN. To identify its function, the alt5 was expressed in Aspergillus oryzae. The transformant produced a new polyketide compound, named alternapyrone. Feeding experiments confirmed that alternapyrone is a decaketide with octa-methylation from methionine on every C2 unit derived from malonyl-CoA except the third one. An iPKS gene, named pksF, was also cloned from A. solani. The A. oryzae transformant with pksF produced two new polyene products, named aslanipyrone and aslaniol, with additioonal more than 9 polyene compounds with different carbon-lengths and cyclization. To clone the iPKS for solanapyrone biosynthesis, we continued a molecular genetic approach with newly designed degenerate primers and cloned four additional iPKS gene fragments AS1~4 from the fungus. Genomic walking from the AS2 fragment identified the presence of biosynthetic gene cluster for reduced-type polyketide consisting of sol1~6 genes. Since the A. oryzae transformant with sol1 for iPKS produced desmethylprosolanapyrone I, a biosynthetic precursor of solanapyrone, the sol gene cluster was identified to be a gene cluster for solanapyrone biosynthesis.