Emission and biosynthesis of volatile terpenoids from the plasmodial slime mold Physarum polycephalum.

Xinlu Chen,Wangdan Xiong,Feng Chen,Guo Wei,Tobias G Köllner

doi:10.3762/bjoc.15.281

Abstract

Terpene synthases (TPSs) are pivotal enzymes for the production of diverse terpenes, including monoterpenes, sesquiterpenes, and diterpenes. In our recent studies, dictyostelid social amoebae, also known as cellular slime molds, were found to contain TPS genes for making volatile terpenes. For comparison, here we investigated Physarum polycephalum, a plasmodial slime mold also known as acellular amoeba. Plasmodia of P. polycephalum grown on agar plates were found to release a mixture of volatile terpenoids consisting of four major sesquiterpenes (α-muurolene, (E)-β-caryophyllene, two unidentified sesquiterpenoids) and the monoterpene linalool. There were no qualitative differences in terpenoid composition at two stages of young plasmodia. To understand terpene biosynthesis, we analyzed the transcriptome and genome sequences of P. polycephalum and identified four TPS genes designated PpolyTPS1–PpolyTPS4. They share 28–73% of sequence identities. Full-length cDNAs for the four TPS genes were cloned and expressed in Escherichia coli to produce recombinant proteins, which were tested for sesquiterpene synthase and monoterpene synthase activities. While neither PpolyTPS2 nor PpolyTPS3 was active, PpolyTPS1 and PpolyTPS4 were able to produce sesquiterpenes and monoterpenes from the respective substrates farnesyl diphosphate and geranyl diphosphate. By comparing the volatile profile of P. polycephalum plasmodia and the in vitro products of PpolyTPS1 and PpolyTPS4, it was concluded that most sesquiterpenoids emitted from P. polycephalum were attributed to PpolyTPS4. Phylogenetic analysis placed the four PpolyTPSs genes into two groups: PpolyTPS1 and PpolyTPS4 being one group that was clustered with the TPSs from the dictyostelid social amoeba and PpolyTPS2 and PpolyTPS3 being the other group that showed closer relatedness to bacterial TPSs. The biological role of the volatile terpenoids produced by the plasmodia of P. polycephalum is discussed.

Highlights

Volatile organic compounds (VOCs) are used by many living organisms as chemical languages for communication [1,2]
To determine whether P. polycephalum releases volatile terpenoids like dictyostelid social amoebae, plasmodia of P. polycephalum were cultured on agar plates with oak flakes as nutrient source and subjected to volatile profiling at two time points: 8 days and 18 days after the transfer of plasmodia to a fresh agar plate
We have successfully identified and characterized terpene synthase (TPS) genes that are involved in making volatile terpenoids from a plasmodial slime mold Physarum polycephalum

Summary

Introduction

Volatile organic compounds (VOCs) are used by many living organisms as chemical languages for communication [1,2]. The chemical diversity of microbial VOCs is continuingly to be discovered, our understanding of their biosynthesis is . Among the diverse VOCs, terpenoids are the largest group. Terpenoids are biosynthesized from two C5 diphosphate compounds isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP), which are produced by either the mevalonate (MVA) pathway or the methylerythritol phosphate (MEP) pathway [9,10]. Terpene synthases (TPSs) catalyze the conversion of prenyl diphosphates to diverse terpenes [13]. Because all living organisms produce prenyl diphosphates, whether an organism has the ability to produce terpenes depends on whether it contains TPS genes

Results

Discussion

Conclusion