UV-Induced Mutants of Metarhizium anisopliae: Improved Biological Parameters, Resistance to Stressful Factors, and Comparative Transcriptomic Analysis

<i>Metarhizium anisopliae</i>, a well-known species of entomopathogenic fungi with great potential as a biological control agent, is vulnerable to UV damage, which restricts its use in the field. To improve the fungal resistance to UV irradiation, UV-induced mutant strains of <i>M. anisopliae</i> s. l. were screened and compared with the wild-type (WT) strain for heat resistance, growth rate, conidial yield, and virulence. Comparative transcriptomic analysis between the selected UV-resistant mutants and the WT was carried out. The results showed that the five mutants exhibited significantly higher heat resistance and growth rates, while the conidial production remained unchanged. Among them, the mutant MaUV-22 exhibited enhanced tolerance to heat, oxidative, osmotic, and SDS stresses as well as increased virulence against <i>Galleria mellonella</i>. Moreover, the transcriptome analysis of MaUV-22 revealed that the expression of genes associated with the heat shock protein pathway, glutathione S-transferase, and thioredoxin reductase were increased dramatically, while the expression of genes related to the catalase and superoxide dismutase pathways was downregulated. The UV-induction technique is an effective strategy to improve fungal resistance to environmental stresses and affords some other beneficial traits such as better control efficacy of entomopathogenic fungi against pests in the field.