High photoreactivation activities of Rad2 and Rad14 in recovering insecticidal Beauveria bassiana from solar UV damage

Abstract

Anti-ultraviolet (UV) roles of Rad2 and Rad14 depend on nucleotide excision repair (NER) of UV-induced DNA lesions in budding yeast but remain unexplored yet in filamentous fungi. Here, nucleus-specific Rad2 and Rad14 orthologs are shown to recover Beauveria bassiana, a main source of wide-spectrum mycoinsecticides, from solar UV damage through photorepair-depending photoreactivation. As a photorepair index, photoreactivation (germination) rates of lethal UVB dose-irradiated conidia via a 3- or 5-h light plus 9- or 7-h dark incubation at 25 °C were drastically reduced in the Δrad2 and Δrad14 mutants versus a wild-type strain. As an NER index, nighttime-mimicking 12-h dark reactivation rates of low UVB dose-impaired conidia decreased sharply compared to the corresponding photoreactivation rates in the presence or absence of either ortholog, indicating that its extant NER activity was limited to recovering light UVB damage in the field. The high photoreactivation activity of either Rad2 or Rad14 was derived from its tight link to a large protein complex formed by photolyase regulators and other anti-UV proteins through multiple protein-protein interactions revealed by yeast two-hybrid assays. Therefore, Rad2 and Rad14 recover B. bassiana from solar UV damage through photoreactiovation in vivo that depends primarily on photorepair, although they contribute little to the fungal lifecycle-related phenotypes. These findings unveil a novel scenario distinguished from the NER-depending anti-UV roles of Rad2 and Rad14 in the model yeast and broaden a biological basis crucial for rational application of fungal insecticides to improve pest control efficacy via feasible recovery of solar UV damage.

Keywords: Anti-UV proteins; Dark reactivation; Fungal insecticides; Photoreactivation; Solar UV damage.