The effect of group IV chitinase, HaCHT4, on the chitin content of the peritrophic matrix (PM) during larval growth and development of Helicoverpa armigera

Nepenthes chitinase NkChit2b- 1 confers broad-spectrum resistance to chitin-containing pathogens and insects in plants

Chitinases play critical roles in plant-pathogen/insect interactions by degrading chitin, a key structural component of fungal cell walls and insect exoskeletons. However, current research lacks comprehensive studies on the broad-spectrum disease resistance of chitinases, and novel chitinases with higher enzymatic activity remain underexplored. Here, we report the prokaryotic expression and functional characterization of Nepenthes khasiana-derived chitinase NkChit2b-1, demonstrating its capacity to confer broad-spectrum resistance against chitin-containing phytopathogenic fungi and insect pests. Biochemical assays revealed that NkChit2b-1 exhibits high enzymatic activity within the optimal temperature range (28-42°C) for terrestrial plant growth and the pH range (5.0-6.0) encompassing pathogen-induced apoplastic alkalization in plants. This enzymatic profile correlates with its effective inhibition of mycelial growth in major phytopathogens including Sclerotinia sclerotiorum, Botrytis cinerea, and Magnaporthe oryzae. Exogenous application of NkChit2b-1 conferred enhanced resistance to these pathogens in both model species (e.g., Arabidopsis) and crop species (e.g., tobacco, tomato, and rice). Intriguingly, NkChit2b-1 pretreatment suppressed feeding activity of brown planthopper (BPH, Nilaparvata lugens) nymphs on rice phloem sap and induced mortality in adult BPH upon ingestion. Furthermore, NkChit2b-1 accelerated beet armyworm (Spodoptera exigua) egg hatching while delaying larval development. In addition, foliar application of NkChit2b-1 on Arabidopsis leaves conferred antifeedant activity against beet armyworm larvae in dual-choice assays. These results collectively indicate the exceptional potential of NkChit2b-1 as an eco-friendly "green pesticide". The exploration of novel chitinases and combinatorial chitinase strategies may overcome the limitations of single-enzyme formulations, thereby advancing chitinase applications in sustainable agriculture and plant protection.

Exploring the role of CYP6AB328 in spinetoram resistance and growth and development of Phthorimaea absoluta

Phthorimaea absoluta is a major agricultural pest, affecting tomatoes and other solanaceous crops. Insect cytochrome P450 is a key enzyme that metabolizes xenobiotics (insecticides and plant toxins) and regulates endogenous compounds, but the functions of specific CYP genes in P. absoluta remain unclear. This study analyzed the expression pattern of 97 CYP genes in two regional populations of P. absoluta from Xinjiang, China. CYP6AB328 was identified as the most significantly overexpressed in the strain from Yining city (YN) compared to the strain from Alaer city (Ala), its expression level exhibited a positively correlated with the accumulating resistance of spinetoram. Following the cloning and sequence analysis of the target gene, it was named CYP6AB328. Additionally, a leaflet delivery system demonstrated the relatively stable presence of dsCYP6AB328 in the leaves from 12 to 24 h. The expression level of CYP6AB328 was significantly reduced by 68.9 % in 2nd instar larvae treated with 7.5 μg/200 μL dsCYP6AB328 at 48 h. Knockdown CYP6AB328 significantly increased susceptibility to spinetoram in the SPI-S strain (belongs to YN strain) and markedly decreased the spinetoram resistance ratio in the resistant strain (SPI-R: 250.57-fold). Notably, silencing CYP6AB328 inhibited nearly all 1st instar larvae fully mining the leaves, resulting in mortality up to 95.3 %, while in 2nd instar larvae, it prolonged leaf-mining time, reduced leaf damage, extended the development time of 2nd to 4th instar, caused 18 % larval abnormality and achieved an 84.4 % mortality on the 6th day of treatment. In summary, our findings indicate that CYP6AB328 plays an important role in promoting development of spinetoram resistance and growth and development of P. absoluta.

Correlative analysis of transcriptome and 16S rDNA in Procambarus clarkii reveals key signaling pathways are involved in Chlorantraniliprole stress response by phosphoinositide 3-kinase (PI3K)

Chlorantraniliprole (CAP), a diamide insecticide, is extensively used in agricultural production. With the increasing adoption of the rice-crayfish integrated farming model, pesticide application has become more frequent. However, the potential risk of CAP to crayfish (Procambarus clarkii) remains unclear. In this study, crayfish were exposed to 30, 60, 90 mg/L CAP for 96 h. As CAP exposure time and concentration increased, crayfish survival rates and total hemocyte counts (THC) decreased. Biochemical indicators revealed that CAP exposure induced oxidative stress and immunosuppression in crayfish, leading to metabolic disorders and reduced ATP content. Additionally, pathological analysis and 16S rDNA sequencing demonstrated that CAP exposure compromised the intestinal barrier of crayfish, altered the intestinal microbial community structure, and caused apoptosis. Differential gene expression analysis showed that CAP exposure significantly suppressed the expression of genes related to immune and energy metabolism pathways, resulting in immune dysfunction and insufficient energy supply, while activating the PI3K/AKT/mTOR signaling pathway. PI3K knockdown reduced antioxidant and digestive activities, increased the expression of proinflammatory and apoptosis genes, and exacerbated CAP-induced intestinal toxicity. This study is the first to explore the characterization and function of PI3K in crustaceans, providing new insights for further research on crustacean antioxidants and defense mechanisms.

Crucial roles of specialized chitinases in elytral and hindwing cuticles construction in Leptinotarsa decemlineata

BACKGROUND

The Colorado potato beetle (CPB), Leptinotarsa decemlineata, is a major potato (Solanum tuberosum) pest, infesting over 16 million km2 and causing substantial economic losses. The insect cuticle forms an apical extracellular matrix (ECM) envelope covering exposed organs to direct morphogenesis and confer structural protection. While select chitinase (Cht) genes have proven essential for larval development, their potential activities directing ECM remodeling underlying adult wing maturation remain undefined.

RESULTS

We investigated the expression patterns and performed an oral RNA interference (RNAi) screen targeting 19 LdChts in late-instar L. decemlineata larvae. Subsequently, we assessed their effects on adult eclosion and wing characteristics. Knockdown of LdCht5, LdCht7, LdCht10, LdIDGF2, and LdIDGF4, as well as others from Group IV (LdCht15, LdCht12, LdCht17, and LdCht13) and Groups VII-X (LdCht2, LdCht11, LdCht1, and LdCht3), resulting in shrunken, misshapen elytra with reduced areal density, as well as transverse wrinkling and impaired wing-tip folding in hindwings. Scanning electron micrographs revealed eroded elytral ridges alongside thinned, ruptured hindwing veins, indicative of mechanical fragility post-LdCht suppression. Spectroscopic analysis uncovered biomolecular alterations underlying the elytral anomalies, including decreases in peaks representing chitin, proteins, and lipids. This loss of essential ECM components provides evidence for the fragility, wrinkling, and shrinkage observed in the RNAi groups.

CONCLUSION

Our findings elucidate the crucial role of chitinases in the turnover of chitinous cuticles on beetle wings, offering insights into RNAi-based control strategies against this invasive pest. © 2024 Society of Chemical Industry.

Function analysis and characterisation of a novel chitinase, MdCht9, in Musca domestica

Insect chitinases have been proposed as potential targets for pest control. In this work, a novel group IV chitinase gene, MdCht9, from Musca domestica was found to have multiple functions in the physiological activity, including chitin regulation, development and antifungal immunity. The MdCht9 gene was cloned and sequenced, its phylogeny was analysed and its expression was determined in normal and 20E treated larvae. Subsequently, RNA interference (RNAi)-mediated MdCht9 knockdown was performed, followed by biochemical assays, morphological observations and transcriptome analysis. Finally, the recombinant protein MdCht9 (rMdCht9) was purified and tested for anti-microbial activity and enzyme characteristics. The results showed that MdCht9 consists of three domains, highly expressed in a larval salivary gland. RNAi silencing of MdCht9 resulted in significant down-regulation of chitin content and expression of 15 chitin-binding protein (CBP) genes, implying a new insight that MdCht9 might regulate chitin content by influencing the expression of CBPs. In addition, more than half of the lethality and partial wing deformity appeared due to the dsMdCht9 treatment. In addition, the rMdCht9 exhibited anti-microbial activity towards Candida albicans (fungus) but not towards Escherichia coli (G-) or Staphylococcus aureus (G+). Our work expands on previous studies of chitinase while providing a potential target for pest management.

Functional importance of groups I and II chitinases, CHT5 and CHT10, in turnover of chitinous cuticle during embryo hatching and post-embryonic molting in the red flour beetle, Tribolium castaneum

Chitinases (CHT) comprise a large gene family in insects and have been classified into at least eleven subgroups. Many studies involving RNA interference (RNAi) have demonstrated that depletion of group I (CHT5s) and group II (CHT10s) CHT transcripts causes lethal molting arrest in several insect species including the red flour beetle, Tribolium castaneum, presumably due to failure of degradation of chitin in their old cuticle. In this study we investigated the functions of CHT5 and CHT10 in turnover of chitinous cuticle in T. castaneum during embryonic and post-embryonic molting stages. RNAi and transmission electron microscopic (TEM) analyses indicate that CHT10 is required for cuticular chitin degradation at each molting period analyzed, while CHT5 is essential for pupal-adult molting only. We further analyzed the functions of these genes during embryogenesis in T. castaneum. Real-time qPCR analysis revealed that peak expression of CHT10 occurred prior to that of CHT5 during embryonic development as has been observed at post-embryonic molting periods in several other insect species. With immunogold-labeling TEM analysis using a fluorescein isothiocyanate-conjugated chitin-binding domain protein (FITC-CBD) probe, chitin was detected in the serosal cuticle but not in any other regions of the eggshell including the chorion and vitelline membrane layers. Injection of double-stranded RNA (dsRNA) for CHT5 (dsCHT5), CHT10 (dsCHT10) or their co-injection (dsCHT5/10) into mature adult females had no effect on their fecundity and the resulting embryos developed normally inside the egg. There were no obvious differences in the morphology of the outer chorion, inner chorion and vitelline membrane among eggs from these dsRNA-treated females. However, unlike dsCHT5 eggs, dsCHT10 and dsCHT5/10 eggs exhibited failure of turnover of the serosal cuticle in which the horizontal chitinous laminae remained intact, resulting in lethal embryo hatching defects. These results indicate that group I CHT5 is essential for pupal-adult molting, whereas group II CHT10 plays an essential role in cuticular chitin degradation in T. castaneum during both embryonic hatching and all of the post-embryonic molts. CHT10 can serve in place of CHT5 in chitin degradation, except during the pupal-adult molt when both enzymes are indispensable to complete eclosion.

Disruption of peritrophic matrix chitin metabolism and gut immune by chlorantraniliprole results in pathogenic bacterial infection in Bombyx mori

Chlorantraniliprole (CAP) is widely used in pest control, and its environmental residues affect the disease resistance of non-target insect silkworms. Studies have demonstrated that changes in gut microbial communities of insects are associated with susceptibility to pathogens. In the present study, we examined the effects of CAP exposure on the immune system and gut microbial community structure of silkworms. The results showed that after 96 h of exposure to low-concentration CAP, the peritrophic matrix (PM) of silkworm larvae was disrupted, and pathogenic bacteria invaded hemolymph. The trehalase activity in the midgut was significantly decreased, while the activities of chitinase, β-N-acetylglucosaminidase, and chitin deacetylase were increased considerably, resulting in decreased chitin content in PM. In addition, exposure to CAP reduced the expressions of key genes in the Toll, IMD, and JAK/STAT pathways, ultimately leading to the downregulation of antimicrobial peptides (AMPs) genes and alterations in the structure of the gut microbial community. Therefore, after infection with the conditional pathogen Enterobacter cloacae (E. cloacae), CAP-exposed individuals exhibited significantly lower body weight and higher mortality. These findings showed that exposure to low-concentration CAP impacted the biological defense system of silkworms, changed the gut microbial community structure, and increased silkworms' susceptibility to bacterial diseases. Collectively, these findings provided a new perspective for the safety evaluation of low-concentration CAP exposure in sericulture.