LAUSR

The filamentous fungus Aspergillus oryzae has 27 putative iterative type I polyketide synthase (PKS) gene clusters, but the secondary metabolites produced by them are mostly unknown. Here, we focused on eight clusters that were reported to be expressed at relatively high levels in a transcriptome analysis. By comparing metabolites between an octuple‐deletion mutant of these eight PKS gene clusters and its parent strain, we found that A. oryzae produced 2,4′‐dihydroxy‐3′‐methoxypropiophenone (1) and its precursor, 4′‐hydroxy‐3′‐methoxypropiophenone (3) in a specific liquid medium. Furthermore, an iterative type I PKS (PpsB) encoded by AO090102000166 and an acetyl‐CoA ligase (PpsA) encoded downstream from ppsB were shown to be essential for their biosynthesis. PpsC, encoded upstream from ppsB, was shown to have 3‐binding activity (Kd=26.0±6.2 μM) and is suggested to be involved in the conversion of 3 to 1. This study deepens our understanding of cryptic secondary metabolism in A. oryzae.