A longevity assurance gene homolog of tomato mediates resistance to Alternaria alternata f. sp lycopersici toxins and fumonisin B-1

The phytopathogenic fungus Alternaria alternata f. sp, lycopersici (AAL) pr oduces toxins that are essential for pathogenicity of the fungus on tomato (Lycopersicon esculentum). AAL toxins and fumonisins of the unrelated fungu s Fusarium moniliforme are sphinganine-analog mycotoxins (SAMs), which caus e inhibition of sphingolipid biosynthesis in vitro and are toxic for some p lant species and mammalian cell lines. Sphingolipids can be determinants in the proliferation or death of cells. We investigated the tomato Alternaria stem canker (Asc) locus, which mediates resistance to SAM-induced apoptosi s. Until now, mycotoxin resistance of plants has been associated with detox ification and altered affinity or absence of the toxin targets. Here we sho w that SAM resistance of tomato is determined by Asc-1, a gene homologous t o the yeast longevity assurance gene LAG1 and that susceptibility is associ ated with a mutant Asc-1. Because both sphingolipid synthesis and LAG1 faci litate endocytosis of glycosylphosphatidylinositol-anchored proteins in yea st, we propose a role for Asc-1 in a salvage mechanism of sphingolipid-depl eted plant cells.