Validamycin Inhibits the Synthesis and Metabolism of Trehalose and Chitin in the Oriental Fruit Fly, Bactrocera dorsalis (Hendel)

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a notorious invasive pest that has raised concerns worldwide. Validamycin has been demonstrated to be a very strong inhibitor against trehalase in a variety of organisms. However, whether validamycin can inhibit trehalase activity to suppress trehalose hydrolysis and affect any other relevant physiological pathways in B. dorsalis remains unknown. In this study, the effects of validamycin injection on the synthesis and metabolism of trehalose and chitin were evaluated. The results show that validamycin injection significantly affected trehalase activity and caused trehalose accumulation. In addition, the downstream pathways of trehalose hydrolysis, including the synthesis and metabolism of chitin, were also remarkably affected as the expressions of the key genes in these pathways were significantly regulated and the chitin contents were changed accordingly. Intriguingly, the upstream trehalose synthesis was also affected by validamycin injection due to the variations in the expression levels of key genes, especially BdTPPC1. Moreover, BdTPPC1 was predicted to have a binding affinity to validamycin, and the subsequent in vitro recombinant enzyme activity assay verified the inhibitory effect of validamycin on BdTPPC1 activity for the first time. These findings collectively indicate that validamycin can be considered as a promising potential insecticide for the management of B. dorsalis.

Identification and RNAi-based functional analysis of chitinase family genes in Agrotis ipsilon

BACKGROUND

Chitin is a major component in the extracellular matrix of insects, and its metabolism largely affects insect development and molting. As essential degradative enzymes, chitinases are encoded by multiple genes that differ in size, expression pattern and function in insects. However, our limited knowledge on the functions of different chitinases in Agrotis ipsilon has prevented our application of new technologies to target these genes as new pest management strategies.

RESULTS

We revealed 11 full-length complementary DNA sequences of chitinase genes (AiChts) from A. ipsilon transcriptome. Although the domain architecture of these chitinases varied greatly, they all contained at least one chitinase catalytic domain. Developmental stage- and tissue-dependent expression profiles showed that most AiChts had the highest expression in the pupal stage. Furthermore, AiCht2, AiCht6, AiCht7 and AiCht10 were mainly expressed in the integument, whereas AiCht8 and AiCht-h had the highest expression in the midgut. The RNA interference (RNAi) experiment revealed that knockdown of AiCht10 or the imaginal disc growth factor gene (AiIDGF) induced high larval mortality. Larvae failed to shed the old cuticle during molting after the injection of double-stranded RNA targeting AiCht10 (dsAiCht10), whereas the larval bodies shrunk and blackened after the injection of dsRNA targeting AiIDGF (dsAiIDGF).

CONCLUSION

Our results revealed for the first time the important functions of AiCht10 and AiIDGF in A. ipsilon. These genes are essential for larval development, and can potentially serve as new targets for RNAi-based pest management. © 2022 Society of Chemical Industry.

MicroRNA miR-8 regulates multiple growth factor hormones produced from Drosophila fat cells

Metabolic organs such as the liver and adipose tissue produce several peptide hormones that influence metabolic homeostasis. Fat bodies, the Drosophila counterpart of liver and adipose tissues, have been thought to analogously secrete several hormones that affect organismal physiology, but their identity and regulation remain poorly understood. Previous studies have indicated that microRNA miR-8, functions in the fat body to non-autonomously regulate organismal growth, suggesting that fat body-derived humoral factors are regulated by miR-8. Here, we found that several putative peptide hormones known to have mitogenic effects are regulated by miR-8 in the fat body. Most members of the imaginal disc growth factors and two members of the adenosine deaminase-related growth factors are up-regulated in the absence of miR-8. Drosophila insulin-like peptide 6 (Dilp6) and imaginal morphogenesis protein-late 2 (Imp-L2), a binding partner of Dilp, are also up-regulated in the fat body of miR-8 null mutant larvae. The fat body-specific reintroduction of miR-8 into the miR-8 null mutants revealed six peptides that showed fat-body organ-autonomous regulation by miR-8. Amongst them, only Imp-L2 was found to be regulated by U-shaped, the miR-8 target for body growth. However, a rescue experiment by knockdown of Imp-L2 indicated that Imp-L2 alone does not account for miR-8's control over the insect's growth. Our findings suggest that multiple peptide hormones regulated by miR-8 in the fat body may collectively contribute to Drosophila growth.