Two white collar proteins protect fungal cells from solar UV damage by their interactions with two photolyases in Metarhizium robertsii

Abstract

The photolyases PHR1 and PHR2 enable photorepair of fungal DNA lesions in the forms of UV-induced cyclobutane pyrimidine dimer (CPD) and (6-4)-pyrimidine-pyrimidone (6-4PP) photoproducts, but their regulation remains mechanistically elusive. Here, we report that the white collar proteins WC1 and WC2 mutually interacting to form a light-responsive transcription factor regulate photolyase expression required for fungal UV resistance in the insect-pathogenic fungus Metharhizum robertsii. Conidial UVB resistance decreased by 54% in Δwc1 and 67% in Δwc2. Five-hour exposure of UVB-inactivated conidia to visible light resulted in photoreactivation rates of 30% and 9% for the Δwc1 and Δwc2 mutants, contrasting to 79%-82% for wild-type and complemented strains. Importantly, abolished transcription of phr1 in Δwc-2 and of phr2 in Δwc1 resulted in incapable photorepair of CDP and 6-4PP DNA lesions in UVB-impaired Δwc2 and Δwc1 cells respectively. Yeast two-hybrid assays revealed interactions of either WC protein with both PHR1 and PHR2. Therefore, the essential roles for WC1 and WC2 in both photorepair of UVB-induced DNA lesions and photoreactivation of UVB-inactivated conidia rely upon their interactions with, and hence transcriptional activation of, PHR1 and PHR2. These findings uncover a novel WC-cored pathway that mediates filamentous fungal response and adaptation to solar UV irradiation.