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Effects of Cordycepin in Cordyceps militaris during Its Infection to Silkworm Larvae.

ABSTRACT: Cordyceps militaris produces cordycepin, a secondary metabolite that exhibits numerous bioactive properties. However, cordycepin pharmacology in vivo is not yet understood. In this study, the roles of cordycepin in C. militaris during its infection were investigated. After the injection of conidia, C. militaris NBRC100741 killed silkworm larvae more rapidly than NBRC103752. At 96 and 120 h, Cmcns genes (Cmcns1-4), which are part of the cordycepin biosynthesis gene cluster, were expressed in fat bodies and cuticles. Thus, cordycepin may be produced in the infection of silkworm larvae. Further, cordycepin enhanced pathogenicity toward silkworm larvae of Metarhizium anisopliae and Beauveria bassiana, that are also entomopathogenic fungi and do not produce cordycepin. In addition, by RNA-seq analysis, the increased expression of the gene encoding a lipoprotein 30K-8 (Bmlp20, KWMTBOMO11934) and decreased expression of genes encoding cuticular proteins (KWMTBOMO13140, KWMTBOMO13167) and a serine protease inhibitor (serpin29, KWMTBOMO08927) were observed when cordycepin was injected into silkworm larvae. This result suggests that cordycepin may aid the in vivo growth of C. militaris in silkworm larvae by the influence of the expression of some genes in silkworm larvae.

SUBMITTER: Kato T

PROVIDER: S-EPMC8065576 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Hypocrealean entomopathogenic fungi (EPF) (Sordariomycetes, Ascomycota) are natural regulators of insect populations in terrestrial environments. Their obligately-killing life-cycle means that there is likely to be strong selection pressure for traits that allow them to evade the effects of the host immune system. In this study, we quantified the effects of cordycepin (3'-deoxyadenosine), a secondary metabolite produced by Cordyceps militaris (Hypocreales, Cordycipitaceae), on insect susceptibility to EPF infection and on insect immune gene expression. Application of the immune stimulant curdlan (20 µg ml-1, linear beta-1,3-glucan, a constituent of fungal cell walls) to Drosophila melanogaster S2r+ cells resulted in a significant increase in the expression of the immune effector gene metchnikowin compared to a DMSO-only control, but there was no significant increase when curdlan was co-applied with 25 µg ml-1 cordycepin dissolved in DMSO. Injection of cordycepin into larvae of Galleria mellonella (Lepidoptera: Pyralidae) resulted in dose-dependent mortality (LC50 of cordycepin = 2.1 mg per insect 6 days after treatment). Incubating conidia of C. militaris and Beauveria bassiana (Hypocreales, Cordycipitaceae; an EPF that does not synthesize cordycepin) with 3.0 mg ml-1 cordycepin had no effect on the numbers of conidia germinating in vitro. Co-injection of G. mellonella with a low concentration of cordycepin (3.0 mg ml-1) plus 10 or 100 conidia per insect of C. militaris or B. bassiana caused a significant decrease in insect median survival time compared to injection with the EPF on their own. Analysis of predicted vs. observed mortalities indicated a synergistic interaction between cordycepin and the EPF. The injection of C. militaris and B. bassiana into G. mellonella resulted in increased expression of the insect immune effector genes lysozyme, IMPI and gallerimycin at 72 h post injection, but this did not occur when the EPF were co-injected with 3.0 mg ml-1 cordycepin. In addition, we observed increased expression of IMPI and lysozyme at 48 h after injection with C. militaris, B. bassiana and sham injection (indicating a wounding response), but this was also prevented by application of cordycepin. These results suggest that cordycepin has potential to act as a suppressor of the immune response during fungal infection of insect hosts.

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Effects of Cordycepin in Cordyceps militaris during Its Infection to Silkworm Larvae.

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