Fatty acid synthase (FAS) is a key enzyme in the lipid synthesis pathway, however, its roles in insects remain largely unknown. Here, we firstly identified two FAS genes from the transcriptome dataset of the general cutworm Spodoptera litura, which is a destructive insect pest of many crops. Both SlFAS1 and SlFAS2 were highly expressed in third instar larvae and in their fat bodies. Then, we successfully silenced SlFAS1 in third instar larvae and the content of α-linolenic acid and triglyceride was significantly decreased. Besides that, the effect of FAS on the metamorphic development in S. litura was evaluated. The results indicate that after silencing SlFAS1, the survival rates of S. litura larvae decreased significantly compared to the control groups. Silencing SlFAS1 in fifth instar larvae resulted in more malformed pupae and adults, and the emergence rates were significantly reduced. Furthermore, the ecdysone content in the haemolymph of fifth instar larvae was significantly decreased after silencing SlFAS1. In addition, knocking down SlFAS1 significantly alters the expression of other key genes in the lipogenesis pathway, implying that FAS has an impact on the lipogenesis pathway. The present study deepens the understanding of FAS in insects and provides novel potential targets for managing insect pests.

The high cell density, immobilization and stability of biofilms are ideal characteristics for bacteria in resisting antibiotic therapy. CsgD is a transcription activating factor that regulates the synthesis of curly fimbriae and cellulose in Escherichia coli, thereby enhancing bacterial adhesion and promoting biofilm formation. To investigate the role of CsgD in biofilm formation and stress resistance in bacteria, the csgD deletion mutant ΔcsgD was successfully constructed from the engineered strain E. coli BL21(DE3) using the CRISPR/Cas9 gene-editing system. The results demonstrated that the biofilm of ΔcsgD decreased by 70.07% (p < 0.05). Additionally, the mobility and adhesion of ΔcsgD were inhibited due to the decrease in curly fimbriae and extracellular polymeric substances. Furthermore, ΔcsgD exhibited a significantly decreased resistance to acid, alkali and osmotic stress conditions (p < 0.05). RNA-Seq results revealed 491 differentially expressed genes between the parent strain and ΔcsgD, with enrichment primarily observed in metabolism-related processes as well as cell membrane structure and catalytic activity categories. Moreover, CsgD influenced the expression of biofilm and stress response genes pgaA, motB, fimA, fimC, iraP, ompA, osmC, sufE and elaB, indicating that the CsgD participated in the resistance of E. coli by regulating the expression of biofilm and stress response. In brief, the transcription factor CsgD plays a key role in the stress resistance of E. coli, and is a potential target for treating and controlling biofilm.

Glyphodes pyloalis Walker (G. pyloalis) is a serious pest on mulberry. Due to the increasing pesticide resistance, the development of new and effective environmental methods to control G. pyloalis is needed. Trehalase is an essential enzyme in trehalose hydrolysis and energy supply, and it has been considered a promising target for insect pest control. However, the specific function of trehalase in G. pyloalis has not been reported. In this study, two trehalase genes (GpTre1 and GpTre2) were identified from our previous transcriptome database. The functions of the trehalase in chitin metabolism were studied by injecting larvae with dsRNAs and trehalase inhibitor, Validamycin A. The open reading frames (ORFs) of GpTre1 and GpTre2 were 1,704 bp and 1,869 bp, which encoded 567 and 622 amino acid residues, respectively. Both of GpTre1 and GpTre2 were mainly expressed in the head and midgut. The highest expression levels of them were in 5th instar during different development stages. Moreover, knockdown both of GpTre1 and GpTre2 by the dsRNAs led to significantly decreased expression of chitin metabolism pathway-related genes, including GpCHSA, GpCDA1, GpCDA2, GpCHT3a, GpCHT7, GpCHSB, GpCHT-h, GpCHT3b, GpPAGM, and GpUAP, and abnormal phenotypes. Furthermore, the trehalase inhibitor, Validamycin A, treatment increased the expressions of GpTre1 and GpTre2, increased content of trehalose, and decreased the levels of glycogen and glucose. Additionally, the inhibitor caused a significantly increased cumulative mortality of G. pyloalis larvae on the 2nd (16%) to 6th (41.3%) day, and decreased the rate of cumulative pupation (72.3%) compared with the control group (95.6%). After the activities of trehalase were suppressed, the expressions of 6 integument chitin metabolism-related genes decreased significantly at 24 h and increased at 48 h. The expressions of GpCHSB and GpCHT-h, involved in chitin metabolism pathway of peritrophic membrane in the midgut, increased at 24 h and 48 h, and there were no changes to GpCHT3b and GpPAGM. These results reveal that GpTre1 and GpTre2 play an essential role in the growth of G. pyloalis by affecting chitin metabolism, and this provides useful information for insect pest control in the future.