Deciphering roles of Rad25, Rad3A, Rad3B and Ssl1 in UV damage recovery and insect-pathogenic lifecycle of Beauveria bassiana

Abstract

Rad25, Rad3 and Ssl1 are subunits of the transcription factor TFIIH required for nucleotide excision repair of UV-induced DNA lesions in budding yeast but remain unexplored in non-yeast fungi. Here, we report essential/similar roles of Rad25 ortholog and Rad3B (one of two Rad3 paralogs) in mediating UVB damage recovery, insect-pathogenic lifecycle and gene expression networks of Beauveria bassiana, a wide-spectrum mycoinsecticide vulnerable to solar UV damage. The recovery depended primarily on photoreactivation of UVB-impaired conidia by 3 h light plus 9 h dark incubation mimicking pre-evening daylight time plus nighttime rather than 12 h dark incubation. The photoreactivation activity arose from direct/indirect links of Rad25 and Rad3B to photolyase and photolyase regulators through multiple protein-protein interactions. Moreover, the Δrad25 and Δrad3B mutants were markedly compromised in insect pathogenicity, multiple stress tolerances, and radial growth on some carbon/nitrogen sources, and shared 2995 dysregulated genes associated with the phenotypic changes. By contrast, Rad3A or orthologous Ssl1 showed limited role in conidial thermotolerance or aerial conidiation alone. These findings unveil pleiotropic effects of Rad25 and Rad3B in the fungal lifecycle and reinforce a biophysical basis to exploit fungal anti-UV photoreactivation activity for optimal mycoinsecticide application in late afternoon on sunny summer days.