Characterization of a New Insecticidal Anthraquinone Derivative from an Endophyte of Acremonium vitellinum against Helicoverpa armigera

Endophytic
fungi have proven to be prolific producers of bioactive
secondary metabolites with agricultural applications. In this study,
bioassay-guided isolation of the endophytic fungus Acremonium vitellinum yielded four anthraquinone
derivatives (compounds 1–4), including
a previously undescribed dimethylated derivative of bipolarin, 6,8-di-O-methylbipolarin (1). Their structures were
determined by 1D and 2D nuclear magnetic resonance analysis as well
as high-resolution electrospray ionization mass spectrometry data,
and the absolute configuration of 1 was established by
comparing the calculated and experimental electronic circular dichroism
spectra. The insecticidal activity of the isolated compounds against
the cotton bollworm Helicoverpa armigera was evaluated. The new compound 1 showed the strongest
larvicidal activity against the 3rd instar larvae of H. armigera with an LC50 value of 0.72
mg/mL. In addition, transcriptome sequencing was performed to evaluate
the molecular mechanism of the insecticidal activity. In total, 5732
differentially expressed genes were found, among which 2904 downregulated
genes and 2828 upregulated genes were mainly involved in cell autophagy,
apoptosis, and DNA mismatch repair and replication. The results presented
in this study reveal how 1 exerts its insecticidal effects
against H. armigera via genome-wide
differential gene expression analyses. Our findings suggest that anthraquinone
derivatives are potential biopesticides for cotton bollworm control.