Immune Defense Mechanism of Reticulitermes chinensis Snyder (Blattodea: Isoptera) against Serratia marcescens Bizio

A comprehensive analysis of the defense responses of Odontotermes formosanus (Shiraki) provides insights into the changes during Serratia marcescens infection

BACKGROUND

Odontotermes formosanus (Shiraki) is a highly damaging agroforestry pest. Serratia marcescens is a broad-spectrum insecticidal pathogen and is highly lethal to O. formosanus. However, little is known about the mechanism between them. To improve the biological control of pests, a more in-depth analysis of the interactions between the pests and the pathogens is essential.

RESULTS

We used RNA-seq, enzyme activity assays and real-time fluorescent quantitative PCR (qPCR) to explore the defense responses of O. formosanus against SM1. RNA-seq results showed that 1,160, 2,531 and 4,536 genes were differentially expressed at 3, 6 and 12 h after SM1 infection, and Kyoto Encyclopedia of Genes and Genomes (KEGG) results indicated that immune response and energy metabolism were involved in the defense of O. formosanus against SM1. Reactive oxygen species (ROS) levels and ROS synthesis genes were significantly elevated, and the antioxidant system were induced in O. formosanus after SM1 infection. In addition, the cellular immune genes were affected, and the Toll, immune deficiency (Imd), Janus kinase/signal transducer and activator of transcription (JAK/STAT), c-Jun N-terminal Kinase (JNK) and melanization pathways were activated. In vitro, Oftermicin, an antimicrobial peptide, had a significantly inhibitory effect on SM1. Furthermore, the expression levels and enzyme activities of phosphofructokinase (PFK), lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) and isocitrate dehydrogenase (IDH) in glycolysis and tricarboxylic acid (TCA) cycles were increased.

CONCLUSIONS

Our results clearly demonstrated that O. formosanus defended against SM1 by activating the antioxidant system, innate immunity and energy metabolism. This study would provide useful information for the development of biological controls of O. formosanus.

Molecular mechanism of Serratia marcescens Bizio infection in Reticulitermes chinensis Snyder based on full-length SMRT transcriptome sequencing

Reticulitermes chinensis Snyder is an important pest in forestry and construction and is widely distributed in China. We found that Serratia marcescens Bizio strain SM1 has insecticidal activity to R. chinensis, but the pathogenic mechanism of SM1 to R. chinensis is not clear. Therefore, full-length transcriptome sequencing was performed on R. chinensis infected with SM1 and the control group. A total of 230 differentially expressed genes were identified by comparing SM1 infection group and the control group, among which 103 were downregulated and 127 were upregulated. We found downregulated genes in nine metabolic pathway categories, among which carbohydrate metabolism had the most downregulated genes, followed by energy metabolism and amino acid metabolism. We also found that some downregulated genes were related to pattern recognition receptors, cellular immunity, and humoral immunity, indicating that R. chinensis immunity was negatively affected by SM1 infection. In addition, some genes in signal transduction and genetic information processing pathways were downregulated. In this study, high-throughput full-length transcriptome analysis was used to analyse the pathogenic mechanism of SM1 to R. chinensis. The results of this study provide useful information for exploring the relationship between SM1 and R. chinensis, and provide theoretical support for the future application of SM1 and the prevention and treatment of R. chinensis.

Genome-wide identification of Coptotermes formosanus immune genes and their potential roles in termite control

In recent years, the use of microbes to control termites has attracted increasing attention. It was found that pathogenic bacteria, nematodes, and fungi effectively control termites under laboratory conditions. However, their effects have not been replicated in the field, and one reason for this is the complex immune defense mechanisms of termites, which are mainly regulated by immune genes. Therefore, altering the expression of immune genes may have a positive influence on the biocontrol efficacy of termites. Coptotermes formosanus Shiraki is one of the most economically important termite pests worldwide. Currently, the large-scale identification of immune genes in C. formosanus is primarily based on cDNA library or transcriptome data rather than at the genomic level. In this study, we identified the immune genes of C. formosanus according to genome-wide analysis. In addition, our transcriptome analysis showed that immune genes were significantly downregulated when C. formosanus was exposed to the fungus Metarhizium anisopliae or nematodes.. Finally, we found that injecting dsRNA to inhibit three immune genes (CfPGRP-SC1, CfSCRB3, and CfHemocytin), which recognize infectious microbes, significantly increased the lethal effect of M. anisopliae on termites. These immune genes show great potential for C. formosanus management based on RNAi. These results also increase the number of known immune genes in C. formosanus which will provide a more comprehensive insight into the molecular basis of immunity in termites.