Two photolyases repair distinct DNA lesions and reactivate UVB-inactivated conidia of an insect mycopathogen under visible light.

Fungal conidia serve as active ingredients of fungal insecticides but are sensitive to solar UV irradiation, which impairs dsDNA by inducing the production of cytotoxic cyclobutane pyrimidine dimers (CPDs) and (6-4)-pyrimidine-pyrimidine photoproducts (6-4PPs). This study aims to elucidate how CPD photolyase (Phr1) and 6-4PP photolyase (Phr2) repair DNA damage and photoreactivate UVB-inactivated cells in Beauveria bassiana , a main source of fungal insecticides. Both Phr1 and Phr2 are proven to exclusively localize in the fungal nuclei. Despite little influence on growth, conidiation and virulence, singular deletions of phr1 and phr2 resulted in respective reductions of 38% and 19% in conidial tolerance to UVB irradiation, a sunlight component most harmful to formulated conidia. CPDs and 6-4PPs accumulated significantly more in the cells of Δ phr1 and Δ phr2 than in those of a wild-type strain under a lethal UVB irradiation and were largely or completely repaired by Phr1 in Δ phr2 and Phr2 in Δ phr1 after optimal 5-h exposure to visible light. Consequently, UVB-inactivated conidia of Δ phr1 and Δ phr2 were much less efficiently photoreactivated than the wild-type counterparts. In contrast, overexpression of either phr1 or phr2 in the wild-type strain resulted in marked increases in both conidial UVB resistance and photoreactivation efficiency. These findings indicate essential roles of Phr1 and Phr2 in photoprotection of B. bassiana from UVB damage and unveil exploitable values of both photolyase genes for improved UVB resistance and application strategy of fungal insecticides. IMPORTANCE Protecting fungal cells from the damage of solar UVB irradiation is critical for development and application of fungal insecticides but is mechanistically not understood in Beauveria bassiana , a classic insect pathogen. We unveil that two intranuclear photolyases, namely Phr1 and Phr2, play essential roles in repairing UVB-induced dsDNA lesions through respective decomposition of cytotoxic cyclobutane pyrimidine dimers and (6-4)-pyrimidine-pyrimidine photoproducts and hence reactivating UVB-inactivated cells effectively under visible light. Our findings shed light upon high potential of both photolyase genes for use in improving UVB resistance and application strategy of fungal insecticides.