Daylight length-dependent translocation of VIVID photoreceptor in cells and its essential role in conidiation and virulence of Beauveria bassiana

The fungal insect pathogen Beauveria bassiana has the blue-light photoreceptor VIVID (VVD) but lacks a pigmentation pattern to trace its light responses. Here, we show that the fungal vvd is transcriptionally expressed, and linked to other blue/red photoreceptor genes, in a daylight length-dependent manner. GFP-tagged VVD fusion protein was localized to periphery, cytoplasm and vacuoles of hyphal cells in light/dark (L:D) cycles of 24:0 and 16:8 and aggregated in cytoplasm with shortening daylight until transfer into nuclei in full darkness. Deletion of vvd caused more reduced (91%) conidiation capacity in L:D 12:12 cycle of blue light (450/480 nm) than of yellow-to-red (540-760 nm) and white lights (similar to 70%). The conidiation defect worsened with shortened daylight in different L:D cycles of white light, coinciding well with drastic repression of key activator genes in central development pathway. Intriguingly, the deletion mutant displayed blocked secretion of cuticle-degrading Pr1 proteases, retarded dimorphic transition in insect haemocoel, and hence a lethal action twice longer than those for control strains against Galleria mellonella regardless of the infection passing or bypassing insect cuticle. Conclusively, VVD sustains normal conidiation in a daylight length-dependent manner and acts as a vital virulence factor in B. bassiana.