Chitin synthesis inhibitors： old molecules and new developments

Chitin is the most abundant natural aminopolysaccharide and serves as a structural component of extracellular matrices. It is found in fungal septa, spores, and cell walls, and in arthropod cuticles and peritrophic matrices, squid pens, mollusk shells, nematode egg shells, and some protozoan cyst walls. As prokaryotes, plants and vertebrates including humans do not produce chitin, its synthesis is considered as an attractive target site for fungicides, insecticides, and acaricides. Although no chitin synthesis inhibitor has been developed into a therapeutic drug to treat fungal infections in humans, a larger number of compounds have been successfully launched worldwide to combat arthropod pests in agriculture and forestry. This review summarizes the latest advances on the mode of action of chitin synthesis inhibitors with a special focus on those molecules that act on a postcatalytic step of chitin synthesis.

Validamycin treatment significantly inhibits the glycometabolism and chitin synthesis in the common cutworm,Spodoptera litura

Validamycin,as a broadly applied antibiotic,has been used to control rice sheath blight disease.Furthermore,validamycin was considered as an insecticide to control agricultural pests.Insight into the mechanism of validamycin’s action on insects can provide molecular targets for the control of agricultural pests.In this study,a toxicological test analysis revealed that Spodoptera litura larval growth and development was significantly inhibited and the pupation rate was significantly reduced with the increase of the concentration of validamycin.According to the NMR-based metabolomic analysis,a total of 15 metabolites involved in glycolysis and tricarboxylic acid cycle(TCA)pathways were identified.Additionally,trehalase activities,glucose and chitin contents were significantly downregulated,but the trehalose content was upregulated after exposure to validamycin.Reverse transcription quantitative PCR analysis revealed that the expression level of genes involved in glycolysis,TCA and chitin synthesis were upregulated after treating with validamycin.Further chitin staining also confirmed that chitin content was downregulated at 12 h after validamycin treatment.Our results indicated that validamycin worked via two different molecular mechanisms,one through inhibiting glycometabolism and the other by inhibiting chitin synthesis in S.litura.The information lays a theoretical foundation for further control of S.litura.

Identification of LmUAP1 as a 20-hydroxyecdysone response gene in the chitin biosynthesis pathway from the migratory locust, Locusta migratoria

In Locusta migratoria, we found that two chitin biosynthesis genes, UDP N-acetylglucosamine pyrophosphorylase gene LmUAP1 and chitin synthase gene Lm- CHS1, are expressed mainly in the integument and are responsible for cuticle formation. However, whether these genes are regulated by 20-hydroxyecdysone （20E） is still largely unclear. Here, we showed the developmental expression pattern ofLmUAP1, LmCHS1 and the corresponding 20E titer during the last instar nymph stage of locust. RNA interference （RNAi） directed toward a common region of the two isoforms of LmEcR （LmEcRcom） reduced the expression level of LmUAP1, while there was no difference in the expression of LmCHS1. Meantime, injection of 20E in vivo induced the expression of LmUAP1 but not LmCHS1. Further, we found injection-based RNAi of LmEcRcom resulted in 100% mortality. The locusts failed to molt with no apolysis, and maintained in the nymph stage until death. In conclusion, our preliminary results indicated that LmUAP1 in the chitin biosynthesis pathway is a 20E late-response gene and LmEcR plays an essential role in locust growth and development, which could be a good potential target for RNAi-based pest control.

Characterization and functional analysis of chitinase family genes involved in nymph-adult transition of Sogatella furcifera

Chitinase degrades chitin in the old epidermis or peritrophic matrix of insects,which ensures normal development and metamorphosis.In our previous work,we comprehensively studied the function of SfCht7 in Sogatella furcifera.However,the number and function of chitinase genes in S.furcifera remain unknown.Here,we identified 12 full-length chitinase transcripts from S.furcifera,which included nine chitinase(Cht),two imaginal disc growth factor(IDGF),and one endo-β-N-acetylglucosaminidase(ENGase)genes.Expression analysis results revealed that the expression levels of eight genes(SfCht3,SfCht5,SfCht6-1,SfCht6-2,SfCht7,SfCht8,SfCht10,and SfIDGF2)with similar transcript levels peaked prior to molting of each nymph and were highly expressed in the integument.Based on RNA interference(RNAi),description of the functions of each chitinase gene indicated that the silencing of SfCht5,SfCht10,and SfIDGF2 led to molting defects and lethality.RNAi inhibited the expressions of SfCht5,SfCht7,SfCht10,and SfIDGF2,which led to downregulated expressions of chitin synthase 1(SfCHS1,SfCHS1a,and SfCHS1b)and four chitin deacetylase genes(SfCDA1,SfCDA2,SfCDA3,and SfCDA4),and caused a change in the expression level of two trehalase genes(TRE1 and TRE2).Furthermore,silencing of SfCht7 induced a significant decrease in the expression levels of three wing development-related genes(SfWG,SfDpp,and SfHh).In conclusion,SfCht5,SfCht7,SfCht10,and SfIDGF2 play vital roles in nymph–adult transition and are involved in the regulation of chitin metabolism,and SfCht7 is also involved in wing development;therefore,these genes are potential targets for control of S.furcifera.