A screening for suppressor mutants reveals components involved in the blue light-inhibited sexual filamentation in Cryptococcus neoformans.

Blue light regulates diverse physiological and developmental processes in fungi. Our prior studies demonstrated that the evolutionally conserved Cwc1 and Cwc2 proteins mediate the blue light-inhibited sexual filamentation in Cryptococcus neoformans. To characterize the putative domains of the Cwc1 and Cwc2 proteins, we generated partially deleted versions of these genes under the GPD1 promoter and examined their effects. The results confirmed that LOV and PAS domains are essential for the function of the Cwc1 protein, and the PAS domain and zinc finger DNA-binding motif are also crucial for the Cwc2 protein. To further understand how light inhibits filamentous growth, a genome wide mutant screening was conducted to identify genes important for this process. Mutants which suppressed the light-dependent CWC1 overexpression phenotype and restored mating filamentation were identified. In the one with fully restored filamentation, the T-DNA was found to disrupt the expression of the CWC2 gene. Additionally, a mediator component, the SSN8 gene, known to involve in transcriptional regulation was also identified. Our results demonstrate that Cwc1 and Cwc2 are two central regulators of the C. neoformans photoresponses and the roles of other components identified in the screen are under investigation.