An inducible, nondegradative phytoalexin resistance mechanism in Dictyostelium discoideum is suppressed by mutations that alter membrane sterol composition

Abstract

Pretreatment of Dictyostelium discoideum amoebae with a sublethal concentration of the pea phytoalexin pisatin was shown to induce nondegradative resistance to subsequent challenges with inhibitory concentrations. An alteration of membrane sterol composition either with the azasterol A25822B or by mutations in nysC that confer resistance to the polyene antibiotic nystatin suppressed the induction of pisatin resistance. Wild-type cells grown on pisatin medium acquired resistance to nystatin; however, after transfer to nystatin medium, they lost their pisatin resistance phenotype but remained nystatin resistant. To account for this asymmetry in the induction and maintenance of cross-resistance after growth on pisatin and nystatin media, we propose a model in which the two resistance phenotypes are governed by distinct mechanisms. This model presumes that growth on pisatin induces membrane alterations that predispose cells to acquire nystatin resistance but that the pisatin-induced membrane alterations are not maintained in the absence of pisatin.

Glimpses of Dictyostelid research in India

“…Isoflavonoids are antimicrobial compounds present in leguminous plants where microbial infection and injury is observed. They show a unique plant-microbe interaction where the isoflavonoids attract the amoebae to help clear the bacteria from the root lesions of the leguminous plants ( Kasbekar and Papavinasasundaram, 1992a;Prasanna et al, 1998). D. discoideum amoebae attain a non-degradative resistance to pisatin (pea phytoalexin) which could be attributed to nysB sunD as observed in the double knockouts.…”