Arabidopsis AAL-toxin-resistant mutant atr1 shows enhanced tolerance to programmed cell death induced by reactive oxygen species

The fungal AAL-toxin triggers programmed cell death (PCD) through perturbations of sphingolipid metabolism in AAL-toxin-sensitive plants. While Arabidopsis is relatively insensitive to the toxin, the loh2 mutant exhibits increased susceptibility to AAL-toxin due to the knockout of a gene involved in sphingolipid metabolism. Genetic screening of mutagenized loh2 seeds resulted in the isolation of AAL-toxin-resistant mutant atr1.Atr1 displays a wild type phenotype when grown on soil but it develops less biomass than loh2 on media supplemented with 2% and 3% sucrose. Atr1 was also more tolerant to the reactive oxygen species-generating herbicides aminotriazole (AT) and paraquat. Microarray analyses of atr1 and loh2 under AT-treatment conditions that trigger cell death in loh2 and no visible damage in atr1 revealed genes specifically regulated in atr1 or loh2. In addition, most of the genes strongly downregulated in both mutants were related to cell wall extension and cell growth, consistent with the apparent and similar AT-induced cessation of growth in both mutants. This indicates that two different pathways, a first controlling growth inhibition and a second triggering cell death, are associated with AT-induced oxidative stress.