Molecular and functional characterization of a fructose specific transporter from the gray mold fungus Botrytis cinerea

In the gray mold fungus Botrytis cinerea, spore germination and plant infection are stimulated in the presence of nutrients, in particular sugars. Applied at micromolar concentrations, fructose is a more potent inducer of germination than glucose. To test whether preferred fructose uptake is responsible for this effect, and to study the mechanism of fructose transport in B. cinerea, a gene (frt1) encoding a fructose transporter was cloned. FRT1 is highly similar to recently identified fructose transporters of yeasts, but much less to other fungal hexose transporters characterized so far. By using a hexose uptake deficient yeast strain for expression, FRT1 was found to be a high affinity proton coupled symporter specific for fructose but not for glucose. B. cinerea frt1 disruption mutants were created and showed normal vegetative growth and plant infection, but a delay in fructose-induced germination when compared to wild-type. Sugar uptake experiments with both wild-type and mutant conidia showed a higher affinity for glucose than for fructose. Thus, we propose that the specific effect of fructose on germination is not due to transport but rather to an as yet unknown intracellular sensing.