The antifungal plant defensin DmAMP1 interacts with fungal sphingolipids of mannosyldiinositolphosphorylceramide (M(IP) 2 C) class. We screened a Saccharomyces cerevisiae transposon (Tn) mutant library against DmAMP1 and identified one DmAMP1-resistant mutant with the Tn inserted in the M(IP) 2 C biosynthesis gene IPT1 (DmTn11) and one DmAMP1-hypersensitive mutant with the Tn inserted in rDNA (HsTnII). However, tetrad analysis pointed to HsTnII as a spontaneous mutant. Apparently, membranes of DmTn11 lack M(IP) 2 C, whereas membranes of HsTnII have increased M(IP) 2 C levels. In addition, DmTn11 and HsTnII are characterized by increased and reduced oxidative stress resistance/chronological life-span (CL), respectively. A putative involvement of M(IP) 2 C in oxidative stress and CL in yeast is discussed.