UV‐induced mutagenesis of Beauveria bassiana (Hypocreales: Clavicipitaceae) yields two hypervirulent isolates with different transcriptomic profiles

Abstract

BACKGROUND The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) can infest over 300 plant species and cause huge economic losses. Beauveria bassiana (Hypocreales: Clavicipitaceae) is one of the most widely used entomopathogenic fungi (EPF). Unfortunately, the efficacy of B. bassiana against S. frugiperda is quite low. Hypervirulent EPF isolates can be obtained by ultraviolet (UV)‐irradiation. Here we report on the UV‐induced mutagenesis and transcriptomic analysis of B. bassiana. RESULTS The wild‐type (WT) B. bassiana (ARSEF2860) was exposed to UV light to induce mutagenesis. Two mutants (named 6M and 8M) showed higher growth rates, conidial yields, and germination rates compared to the WT strain. The mutants showed higher levels of tolerance to osmotic, oxidative, and UV stresses. The mutants showed higher protease, chitinase, cellulose, and chitinase activities than WT. Both WT and mutants were compatible with the insecticides matrine, spinetoram, and chlorantraniliprole, but incompatible with emamectin benzoate. Insect bioassays showed that both mutants were more virulent against S. frugiperda and the greater wax moth Galleria mellonella. Transcriptomic profiles of the WT and mutants were determined by RNA‐sequencing. The differentially expressed genes (DEGs) were identified. The gene set enrichment analysis (GSEA), protein–protein interaction (PPI) network, and hub gene analysis revealed virulence‐related genes. CONCLUSION Our data demonstrate that UV‐irradiation is a very efficient and economical technique to improve the virulence and stress resistance of B. bassiana. Comparative transcriptomic profiles of the mutants provide insights into virulence genes. These results provide new ideas for improving the genetic engineering and field efficacy of EPF. © 2023 Society of Chemical Industry.

Dual RNA Sequencing of Beauveria bassiana-Infected Spodoptera frugiperda Reveals a Fungal Protease with Entomopathogenic and Antiphytopathogenic Activities

“…Our previous report showed that the insecticidal activity of B. bassiana ARSEF2860 against FAW larvae was rather limited when tested by immersion bioassays . Here, we observed that FAW eggs and pupae were efficiently infected when briefly immersed in Bb2860 conidia (Figure A–E).…”

“…27 Using UV-induced mutagenesis, we obtained two hypervirulent isolates of B. bassiana that exceeded the efficiency of the wild-type strain Bb2860. 21 In this study, the Bb2860 strain can invade FAW eggs and pupae by immersion. Nevertheless, Bb2860 conidia can only infect FAW larvae through injection (Figure 1).…”

“…Our previous report showed that the insecticidal activity of B. bassiana ARSEF2860 against FAW larvae was rather limited when tested by immersion bioassays. 21 Here, we observed that FAW eggs and pupae were efficiently infected when briefly immersed in Bb2860 conidia (Figure 1A−E). Nearly all larvae survived in the immersion bioassay (data not shown), while the intrahemocoel injection of Bb2860 conidia efficiently killed FAW larvae in a dose-dependent manner (Figure 1F−I).…”