Isolation and characterization of gut bacteria associated with the degradation of host-specific terpenoids in Pagiophloeus tsushimanus (Coleoptera: Curculionidae) larvae.

Insect intestinal bacteria play an important role in resisting defensive substances of host plants. Pagiophloeus tsushimanus (Coleoptera: Curculionidae) feeds exclusively on camphor trees (Cinnamomum camphora, Laurales: Lauraceae) in China, causing substantial economic and ecological losses. It is unclear how the larvae of P. tsushimanus outcome the main secondary metabolites of C. camphora such as D-camphor, eucalyptol, and linalool. In this study, we isolated terpenoid-degrading bacteria from the gut of P. tsushimanus larvae by using selective culture medium. Maximum likelihood phylogenetic analyses were performed with 16S rDNA sequences to identify the bacteria, and results showed ten strains belonged to four genera, including Pseudomonas, Enterobacter, Serratia, and Corynebacterium. Then, gas chromatography was employed to determine the degradability of D-camphor, eucalyptol, and linalool by the isolated strains, results showed that Z5 strain (i.e., Corynebacterium variabile, Actinomycetales: Corynebacteriaceae), F1 strain (i.e., Pseudomonas aeruginosa, Pseudomonadales: Pseudomonaceae), and A3 strain (i.e., Serratia marcescens, Enterobacterales: Enterobacteriaceae) had the highest degradation rates of D-camphor, linalool, and eucalyptol, respectively. The intestinal bacteria were capable of terpenoid degradation in vitro, which suggested that these gut bacteria associated with P. tsushimanus play an important role in overcoming host plant secondary metabolite defense, thereby facilitating the host specialization of this pest.

Qiao H ，Zhu H ，Li H ，Chen H ，Li S ，Chen C ，Hao D ... -  《JOURNAL OF INSECT SCIENCE》

Tolerance to dietary linalool primarily involves co-expression of cytochrome P450s and cuticular proteins in Pagiophloeus tsushimanus (Coleoptera: Curculionidae) larvae using SMRT sequencing and RNA-seq.

Pagiophloeus tsushimanus (Coleoptera: Curculionidae), an emerging forest pest exclusively infesting camphor trees, has recently caused severe ecological and economic damage in localized areas in China. Its population outbreak depends largely on the capacity to overcome the pressure of terpenoid-derived metabolites (e.g. linalool) from camphor trees. At present, the molecular basis of physiological adaptation of P. tsushimanus to dietary linalool is poorly understood, and there is no available reference genome or transcriptome. Herein, we constructed the transcriptome profiling of P. tsushimanus larvae reared on linalool-infused diets using RNA sequencing and single-molecule real-time sequencing. A total of 20,325 high-quality full-length transcripts were identified as a reference transcriptome, of which 14,492 protein-coding transcripts including 130 transcription factors (TFs), and 5561 long non-coding RNAs (lncRNAs) were detected. Also, 30 alternative splicing events and 8049 simple sequence repeats were captured. Gene ontology enrichment of differential expressed transcripts revealed that overall up-regulation of both cytochrome P450s (CYP450s) and cuticular proteins (CPs), was the primary response characteristic against dietary linalool. Other physiological effects possibly caused by linalool exposure, such as increase in Reactive Oxygen Species (ROS) and hormetic stimulation, were compensated by a handful of induced genes encoding antioxidases, heat shock proteins (HSPs), juvenile hormone (JH) epoxide hydrolases, and digestive enzymes. Additionally, based on co-expression networks analysis, a diverse array of hub lncRNAs and TFs co-expressed with CYP450s and CPs were screened as the potential gene regulators. Temporal expression of candidate transcripts determined by quantitative real-time PCR also indicated a cooperative relationship between the inductions of CYP450s and CPs upon exposure to linalool. Our present study provides an important transcriptome resource of P. tsushimanus, and lays a valuable foundation for understanding how this specialist pest copes with chemical challenges in its specific host environments.

Li S ，Li H ，Chen C ，Hao D ... -  《BMC GENOMICS》

The Key Phytochemical Cue Camphor Is a Promising Lure for Traps Monitoring the New Monophagous Camphor Tree Borer Pagiophloeus tsushimanus (Coleoptera: Curculionidae).

Chen C ，Xu T ，Li S ，Xue M ，Deng Y ，Fan B ，Yang C ，Hao D ... -  《-》

Identification of algicidal monoterpenoids from four chemotypes of Cinnamomum camphora and their algicidal mechanisms on Microcystis aeruginosa.

Cyanobacterial blooms cause serious environmental issues, and plant secondary metabolites are considered as new algaecide for controlling them. Cinnamomum camphora produces a wide spectrum of terpenoids and has 4 main chemotypes, including linalool, camphor, eucalyptol and borneol chemotype. To develop the new cyanobacterial algaecide by using suitable chemotype of Cinnamomum camphora and the main terpenoids, we analyzed the terpenoid composition in the 4 chemotype extracts, evaluated the algicidal effects of the extracts and their typical monoterpenoids on Microcystis aeruginosa, and investigated the algicidal mechanism of the stronger algicidal agents. Among the 4 chemotypes, eucalyptol and borneol chemotype extracts exhibited stronger algicidal effects. In the 4 chemotype extracts, monoterpenoids were the main compounds, of which linalool, camphor, eucalyptol and borneol were the typical components. Among the 4 typical monoterpenoids, eucalyptol and borneol showed stronger algicidal effects, which killed 78.8% and 100% M. aeruginosa cells, respectively, at 1.2 mM after 48 h. In 1.2 mM eucalyptol and borneol treatments, the reactive oxygen species levels markedly increased, and the caspase-3-like activity also raised. With prolonging the treatment time, M. aeruginosa cells gradually shrank and wrinkled, and the cell TUNEL fluorescence intensity and DNA degradation gradually enhanced, indicating that the lethal mechanism is causing apoptosis-like programmed cell death (PCD). Therefore, eucalyptol and borneol chemotype extracts and their typical monoterpenoids have the potential for developing as algaecides to control cyanobacteria through triggering apoptosis-like PCD.

Huang T ，Lai M ，Lin Z ，Luo R ，Xiang X ，Xu H ，Pan N ，Zuo Z ... -  《-》

Correction to: Isolation and characterization of gut bacteria associated with the degradation of host-specific terpenoids in Pagiophloeus tsushimanus (Coleoptera: Curculionidae) larvae.

《JOURNAL OF INSECT SCIENCE》