Early detection of dry bubble disease in Agaricus bisporus using volatile compounds

Lecanicillium fungicola is a pathogen of the commercial white button mushroom (Agaricus bisporus) and is the causal agent of dry bubble disease, which can cause severe economic losses to mushroom growers. Volatile compounds were measured by GC/MS techniques over pure cultures of mycelia on agars, over microcosms of growing mushrooms, and over harvested mushrooms to identify compounds that might give an early warning of the disease. The mushroom strain tested was Agaricus bisporus, strain Sylvan A15; either deliberately infected with L. fungicola or water as a control. Over microcosms, the appearance of β-copaene, β-cubebene, and α-cedrene coincided with, but did not precede, the earliest visual signs of the disease. Mushrooms with dry bubble symptoms also had high levels of β-barbatene and an unknown diterpene (UK 1821). Over some harvested mushroom sets, high levels of cis-α-bisabolene developed as a defence reaction to infection.

Transcriptome Analysis and Identification of Sesquiterpene Synthases in Liverwort Jungermannia exsertifolia

The liverwort Jungermannia exsertifolia is one of the oldest terrestrial plants and rich in structurally specific sesquiterpenes. There are several sesquiterpene synthases (STSs) with non-classical conserved motifs that have been discovered in recent studies on liverworts; these motifs are rich in aspartate and bind with cofactors. However, more detailed sequence information is needed to clarify the biochemical diversity of these atypical STSs. This study mined J. exsertifolia sesquiterpene synthases (JeSTSs) through transcriptome analysis using BGISEQ-500 sequencing technology. A total of 257,133 unigenes was obtained, and the average length was 933 bp. Among them, a total of 36 unigenes participated in the biosynthesis of sesquiterpenes. In addition, the in vitro enzymatic characterization and heterologous expression in Saccharomyces cerevisiae showed that JeSTS1 and JeSTS2 produced nerolidol as the major product, while JeSTS4 could produce bicyclogermacrene and viridiflorol, suggesting a specificity of J. exsertifolia sesquiterpene profiles. Furthermore, the identified JeSTSs had a phylogenetic relationship with a new branch of plant terpene synthases, the microbial terpene synthase-like (MTPSL) STSs. This work contributes to the understanding of the metabolic mechanism for MTPSL-STSs in J. exsertifolia and could provide an efficient alternative to microbial synthesis of these bioactive sesquiterpenes.

Ancient defensive terpene biosynthetic gene clusters in the soft corals

Diterpenes are major defensive small molecules that enable soft corals to survive without a tough exterior skeleton, and, until now, their biosynthetic origin has remained intractable. Furthermore, biomedical application of these molecules has been hampered by lack of supply. Here, we identify and characterize coral-encoded terpene cyclase genes that produce the eunicellane precursor of eleutherobin and cembrene, representative precursors for the >2,500 terpenes found in octocorals. Related genes are found in all sequenced octocorals and form their own clade, indicating a potential ancient origin concomitant with the split between the hard and soft corals. Eleutherobin biosynthetic genes are colocalized in a single chromosomal region. This demonstrates that, like plants and microbes, animals also harbor defensive biosynthetic gene clusters, supporting a recombinational model to explain why specialized or defensive metabolites are adjacently encoded in the genome.

Contrasting nitrogen and phosphorus fertilization effects on soil terpene exchanges in a tropical forest

Production, emission, and absorption of biogenic volatile organic compounds (BVOCs) in ecosystem soils and associated impacts of nutrient availability are unclear; thus, predictions of effects of global change on source-sink dynamic under increased atmospheric N deposition and nutrition imbalances are limited. Here, we report the dynamics of soil BVOCs under field conditions from two undisturbed tropical rainforests from French Guiana. We analyzed effects of experimental soil applications of nitrogen (N), phosphorus (P), and N + P on soil BVOC exchanges (in particular of total terpenes, monoterpenes, and sesquiterpenes), to determine source and sink dynamics between seasons (dry and wet) and elevations (upper and lower elevations corresponding to top of the hills (30 m high) and bottom of the valley). We identified 45 soil terpenoids compounds emitted to the atmosphere, comprising 26 monoterpenes and 19 sesquiterpenes; of these, it was possible to identify 13 and 7 compounds, respectively. Under ambient conditions, soils acted as sinks of these BVOCs, with greatest soil uptake recorded for sesquiterpenes at upper elevations during the wet season (-282 μg m^-2 h^-1). Fertilization shifted soils from a sink to source, with greatest levels of terpene emissions recorded at upper elevations during the wet season, following the addition of N (monoterpenes: 406 μg m^-2 h^-1) and P (sesquiterpenes: 210 μg m^-2 h^-1). Total soil terpene emission rates were negatively correlated with total atmospheric terpene concentrations. These results indicate likely shifts in tropical soils from sink to source of atmospheric terpenes under projected increases in N deposition under global change, with potential impacts on regional-scale atmospheric chemistry balance and ecosystem function.

A Cryptic Plant Terpene Cyclase Producing Unconventional 18- and 14-Membered Macrocyclic C25 and C20 Terpenoids with Immunosuppressive Activity

A versatile terpene synthase (LcTPS2) producing unconventional macrocyclic terpenoids was characterized from Leucosceptrum canum. Engineered Escherichia coli and Nicotiana benthamiana expressing LcTPS2 produced six 18-/14-membered sesterterpenoids including five new ones and two 14-membered diterpenoids. These products represent the first macrocyclic sesterterpenoids from plants and the largest sesterterpenoid ring system identified to date. Two variants F516A and F516G producing approximately 3.3- and 2.5-fold, respectively, more sesterterpenoids than the wild-type enzyme were engineered. Both 18- and 14-membered ring sesterterpenoids displayed significant inhibitory activity on the IL-2 and IFN-γ production of T cells probably via inhibition of the MAPK pathway. The findings will contribute to the development of efficient biocatalysts to create bioactive macrocyclic sesterterpenoids, and also herald a new potential in the well-trodden territory of plant terpenoid biosynthesis.

Mechanistic Investigations on Microbial Type I Terpene Synthases through Site-Directed Mutagenesis

During the past three decades many terpene synthases have been characterised from all kingdoms of life. Enzymes of type I, from bacteria, fungi and protists, commonly exhibit several highly conserved motifs and single residues, and the available crystal structures show a shared α-helical fold, while the overall sequence identity is generally low. Several enzymes have been studied by site-directed mutagenesis, giving valuable insights into terpene synthase catalysis and the intriguing mechanisms of terpene synthases. Some mutants are also preparatively useful and give higher yields than the wild type or a different product that is otherwise difficult to access. The accumulated knowledge obtained from these studies is presented and discussed in this review.

1 Introduction

2 Residues for Substrate Binding and Catalysis

3 Residues with Structural Function

4 Residues Contouring the Active Site Cavity

5 Other Residues

6 Conclusions

Targeting active site residues and structural anchoring positions in terpene synthases

The sesterterpene synthase SmTS1 from Streptomyces mobaraensis contains several unusual residues in positions that are otherwise highly conserved. Site-directed mutagenesis experiments for these residues are reported that showed different effects, resulting in some cases in an improved catalytic activity, but in other cases in a loss of enzyme function. For other enzyme variants a functional switch was observed, turning SmTS1 from a sesterterpene into a diterpene synthase. This article gives rational explanations for these findings that may generally allow for protein engineering of other terpene synthases to improve their catalytic efficiency or to change their functions.

Microbial volatile organic compounds in intra-kingdom and inter-kingdom interactions

Microorganisms produce and excrete a versatile array of metabolites with different physico-chemical properties and biological activities. However, the ability of microorganisms to release volatile compounds has only attracted research attention in the past decade. Recent research has revealed that microbial volatiles are chemically very diverse and have important roles in distant interactions and communication. Microbial volatiles can diffuse fast in both gas and water phases, and thus can mediate swift chemical interactions. As well as constitutively emitted volatiles, microorganisms can emit induced volatiles that are triggered by biological interactions or environmental cues. In this Review, we highlight recent discoveries concerning microbial volatile compounds and their roles in intra-kingdom microbial interactions and inter-kingdom interactions with plants and insects. Furthermore, we indicate the potential biotechnological applications of microbial volatiles and discuss challenges and perspectives in this emerging research field.