Multiple nucleobase transporters contribute to boscalid sensitivity in Aspergillus nidulans

The development of fungicide-resistant fungal populations represents a major challenge for the agrochemical and agri-food sectors, which threatens food supply and security. The issue becomes complex for fungi that cause quantitative and qualitative losses due to mycotoxin biosynthesis. Nonetheless, currently, the molecular details underlying fungicide action and fungal resistance mechanisms are partially known. Here, we have investigated whether plasma membrane transporters contribute to specific fungicide uptake in the model fungus Aspergillus nidulans. Independent physiological tests and toxicity screening of selected fungicides provided evidence that the antifungal activity of Succinate Dehydrogenase Inhibitors (SDHIs) is associated with the expression of several nucleobase-related transporters. In particular, it was shown that a strain genetically inactivated in all seven nucleobase-related transporters is resistant to the fungicide boscalid, whereas none of the single null mutants exhibited significant resistance level. By constructing and testing isogenic strains that over-express each one of the seven transporters, we confirmed that five of them, namely, UapC, AzgA, FycB, CntA, and FurA, contribute to boscalid uptake. Additionally, by employing metabolomics we have examined the effect of boscalid on the metabolism of isogenic strains expressing or genetically lacking boscalid-related nucleobase transporters. The results confirmed the involvement of specific nucleobase transporters in fungicide uptake, leading to the discovery of corresponding metabolites-biomarkers. This work is the first report on the involvement of specific transporters in fungicide uptake and toxicity and their impact on fungal metabolism regulation and results might be further exploited towards the deeper understanding of fungal resistance to fungicides.