Deciphering the role of ergosterol and sphingolipids in the antifungal mode of action of rhamnolipids on Sclerotiniaceae.

Rhamnolipids (RLs) are natural glycolipids very promising to reduce the use of pesticides to protect crops. They have efficient antifungal properties against Sclerotiniaceae fungi. They are membranotropic compounds permeabilizing fungal cells. We have previously proposed that a lower ergosterol amount could be linked to a lower antifungal sensitivity. The main objective of this paper was to gain insights into the role of plasma membrane lipids in the antifungal mode of action of RLs on Sclerotiniaceae. We obtained ergosterol biosynthesis pathway mutants of Botrytis cinerea and evaluated their sensitivity to RLs. We also analyzed the sphingolipid contents of B. cinerea and S. sclerotiorum and assessed their involvement by a pharmacological approach. We confirm here that a decrease of the ergosterol content in B. cinerea mutants triggers a lower antimycelial activity of RLs. Co-treatments of both mycelium with the polyene natamycin, which specifically binds to ergosterol, show that the ergosterol role in RL activity involves an access of RLs to this lipid. Conversely, we demonstrate that ceramides and acidic glycosphingolipids could have a protective role against the permeabilization property of RLs. These results demonstrate in vivo the antagonistic role of two major membrane lipids in the mode of action of RLs. They also show that the effective use of RLs as antifungal agents within biocontrol strategies requires consideration of differences in the lipid composition of fungi.