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, targeting the plasma membrane to permeabilize fungal cells. We have previously shown that a lower ergosterol amount in Botrytis cinerea could be linked to a lower sensitivity, compared to Sclerotinia sclerotiorum, containing more ergosterol. 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 analyzed in vivo the role of ergosterol and explored the role of sphingolipids. 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 mutants triggers a lower antimycelial activity of RLs. Co-treatments of mycelium with the polyene natamycin, specifically binding ergosterol, show that the ergosterol role in RL activity involves an access to this molecule. We also demonstrate that ceramides and acidic sphingolipids are involved in the permeabilization property of RLs.