The rice pathogen Fusarium fujikuroi produces economically important secondary metabolites like gibberellic acids and carotenoids as well as mycotoxins like bikaverin and fusarin C. Their production is activated in response to environmental stimuli such as light, pH or nutrient availability. In this study, we evaluate the effects of light and different putative light receptors on growth and differentiation as well as secondary metabolism. Bimolecular fluorescence complementation proved that homologs of the Neurospora crassaWhite Collar proteins in F. fujikuroi(WcoA and WcoB) form a nuclear localized complex (WCC) that is needed for full functionality. Deletion and complementation of both genes revealed that the WCC represses bikaverin gene expression in constant light conditions and induces immediate light-dependent carotenoid gene expression as shown by northern blot analyses. Additionally the WCC represses conidiogenesis in response to light. The effects observed regarding bikaverin and carotenoid gene expressions as well as conidiogenesis are antagonistically to the ones observed in the velvet mutant, making a connection between the WCC and the velvet complex feasible, similarly to the situation in Aspergillus nidulans. Since carotenoid production was maintained in both wcoA and wcoB single as well as in wcoA/B double mutants in constant light conditions, we focused on characterization of additional putative light receptors in F. fujikuroi. Deletion of the phytochrome-likeencoding gene fph1 did not show any significant phenotype. Deletion of phl1, coding for a cryptochrome/photolyase demonstrated impaired carotenoid biosynthesis gene expression upon exposure to light. Additionally, gene expression and HPLC analyses of these mutants demonstrated loss of fusarin C gene expression and concomitant production formation compared to the wild type, suggesting a distinct transcriptional activity for this barely characterized class of enzymes. Finally UV mutagenesis experiments and qRT-PCR demonstrate that WcoA, WcoB and Phl1 are involved in UV-damage repair most likely by transcriptionally activating phr1, encoding a CPD-photolyase. The data presented here allow us to draw a first model of how light receptors function in a signaling network in the rice pathogen F. fujikuroi.
Full conference title:
27th Fungal Genetics Conference
- Fungal Genetics Conference 27th (2013)