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Overexpression of the Tomato Asc-1 Gene Mediates High Insensitivity to AAL Toxins and Fumonisin B₁ in Tomato Hairy Roots and Confers Resistance to Alternaria alternata f. sp. lycopersici in Nicotiana umbratica Plants

The sphinganine-analog mycotoxins (SAMs) fumonisin B₁ and AAL toxins are inhibitors of eukaryotic sphinganine N-acyltransferase in vitro. Treatment of eukaryotes with SAMs generally results in an accumulation of sphingoid base precursors and a depletion of complex sphingolipids. The asc,asc genotypes of tomato (Lycopersicon esculentum) and Nicotiana umbratica are sensitive to SAMs and host of the AAL toxin-producing fungus Alternaria alternata f. sp. lycopersici. Codominant insensitivity to SAMs in tomato is mediated by the Asc-1 gene, and sensitivity is associated with a frame-shift mutation present in asc-1. We investigated the function of Asc-1 in mediating insensitivity to SAMs and resistance to the fungus by overexpression of asc-1 and Asc-1. In this study, it is shown that overexpression of these genes did not lead to visual symptoms in tomato hairy roots and N. umbratica plants. Overexpression of asc-1 did not influence the (in)sensitivity to SAMs. Overexpression of Asc-1 in SAM-sensitive hairy roots and N. umbratica plants, however, mediated a high insensitivity to SAMs and resistance to plant infection by Alternaria alternata f. sp. lycopersici.