Abstract

A new type III polyketide synthase gene (Ssars) was discovered from the genome of Shiraia sp. Slf14, an endophytic fungal strain from Huperzia serrata. The intron-free gene was cloned from the cDNA and ligated to two expression vectors pET28a and YEpADH2p-URA3 for expression in Escherichia coli BL21(DE3) and Saccharomyces cerevisiae BJ5464, respectively. SsARS was efficiently expressed in E. coli BL21(DE3), leading to the synthesis of a series of polyketide products. Six major products were isolated from the engineered E. coli and characterized as 1,3-dihydroxyphenyl- 5-undecane, 1,3-dihydroxyphenyl-5-cis-6􍿁-tridecene,1,3-dihydroxyphenyl- 5-tridecane, 1,3-dihydroxyphenyl-5-cis-8􍿁- pentadecene, 1,3-dihydroxyphenyl-5-pentadecane, and 1,3- dihydroxyphenyl-5-cis-10􍿁-heptadecene, respectively, based on the spectral data and biosynthetic origin. Expression of SsARS in the yeast also led to the synthesis of the same polyketide products, indicating that this enzyme can be reconstituted in both heterologous hosts. Supplementation of soybean oil into the culture of E. coli BL21(DE3)/SsARS increased the production titers of 1–6 and led to the synthesis of an additional product, which was identified as 5-(8􍿁Z,11􍿁Z-heptadecadienyl) resorcinol. This work thus allowed the identification of SsARS as a 5-alk(en)ylresorcinol synthase with flexible substrate specificity toward endogenous and exogenous fatty acids. Desired resorcinol derivatives may be synthesized by supplying corresponding fatty acids into the culture medium.

• Keywords: Shiraia sp. Slf14; type III polyketide synthase; alk(en)ylresorcinols; substrate flexibility; precursor-directed biosynthesis