Identification of a putative polyketide synthase gene involved in usnic acid biosynthesis in the lichen Nephromopsis pallescens.

Mei Hua,Yi Wang,Xiaolong Yuan,Changtian Li,Changan Geng,Fenghua Tian

doi:10.1371/journal.pone.0199110

Abstract

Usnic acid is a unique polyketide produced by lichens. To characterize usnic acid biosynthesis, the transcriptome of the usnic-acid-producing lichen-forming fungus Nephromopsis pallescens was sequenced using Illumina NextSeq technology. Seven complete non-reducing polyketide synthase genes and nine highly-reducing polyketide synthase genes were obtained through transcriptome analysis. Gene expression results obtained by qPCR and usnic acid detection with LCMS-IT-TOF showed that Nppks7 is probably involved in usnic acid biosynthesis in N. pallescens. Nppks7 is a non-reducing polyketide synthase with a MeT domain that also possesses beta-ketoacyl-ACP synthase, acyl transferase, product template, acyl carrier protein, C-methyltransferase, and Claisen cyclase domains. Phylogenetic analysis shows that Nppks7and other polyketide synthases from lichens form a unique monophyletic clade. Taken together, our data indicate that Nppks7 is a novel PKS in N. pallescens that is likely involved in usnic acid biosynthesis.

Highlights

Usnic acid is a unique natural compound produced by lichens that has antibacterial [1], antiviral[2], and antitumor[3,4] bioactive properties
Chemoenzymatic synthesis analysis has demonstrated that methylphloracetophenone is the precursor of usnic acid [9], and it was hypothesized that usnic acid biosynthesis is associated with non-reducing polyketide synthase (PKS) with a C-methyltransferase (MeT) domain
To obtain the transcriptome of usnic-acid-producing N. pallescens, an RNA sequencing (RNA-Seq) library was constructed from mycelia and sequenced using Illumina Seq

Summary

Introduction

Usnic acid is a unique natural compound produced by lichens that has antibacterial [1], antiviral[2], and antitumor[3,4] bioactive properties. Several reviews of the bioactive properties of usnic acid have highlighted its pharmaceutical value [5,6,7,8]. Chemoenzymatic synthesis analysis has demonstrated that methylphloracetophenone is the precursor of usnic acid [9], and it was hypothesized that usnic acid biosynthesis is associated with non-reducing polyketide synthase (PKS) with a C-methyltransferase (MeT) domain. The biosynthesis of usnic acid remains unclear. As in the analysis of other lichen metabolites, there are several challenges limiting the application of techniques typically applied to other organisms, such as gene knockout or heterologous expression, to revealing mechanisms of lichen metabolite biosynthesis [10].

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Discussion

Conclusion