Identification of the first steps in phenalenone pigment biosynthesis in Fusarium solani

Most Fusarium species produce bikaverin and aurofusarin for mycelium pigmentation and fusarubins for perithecial pigmentation [1]. However, Fusarium solani produces fusarubins during mycelial growth and another unknown pigment during sexual reproduction. This unknown pigment is predicted to be biosynthesized by a non-reducing polyketide synthase (PKS35 = PKSN [2]). PKS35 encodes a 2106 aa protein and share 52% identity to PhnA from P. herquei, which catalyzes the first step of the herqueinone biosynthetic pathway [3]. Genetic analyses of the PKS35 gene cluster suggests that it contains eleven genes, of which four are present in the herqueinone cluster. Herqueinone contains tricyclic phenalenone core ring structure cyclized by a FAD-dependent monooxygenase. To unravel the biosynthetic products in the PKS35 pathway the intron stripped PKS was cloned and put under control of a galactose inducible promoter in a 2µ vector, which was transformed into a Saccharomyces cerevisiae strain co-expressing a Sfp-Type 4′-Phosphopantetheinyl Transferase (Ppt1). The transformed yeast strain was cultivated under induced conditions in liquid cultures for five days and before production of secondary metabolites
was analyzed by high-resolution mass spectrometry (HRMS). The results showed that the yeast strain was able to produce prephenalenone, which is also the first step of the herqueinone pathway. We also detected dehydroxyprephenalenone, which is formed through spontaneous dehydration [3]. Through heterologous expression of the other genes in the cluster, we will follow the biosynthetic route and ultimately unravel the entire pathway of the perithecial pigment of F. solani.
[1] Studt L, Wiemann P, Kleigrewe K et al (2012): Appl Environ Microbiol, 78: 4468-4480.
[2] Graziani S, Vasnier C, Daboussi MJ (2004): Appl Environ Microbiol, 70: 2984-2988.
[3] Gao SS, Duan A, Xu W et al (2016): J Am Chem Soc, 138: 4249-4259.