Inactivation of UDP-Glucose Sterol Glucosyltransferases Enhances Resistance to .

Free and glycosylated sterols are both structural components of the plasma membrane that regulate their biophysical properties and consequently different plasma membrane-associated processes such as plant adaptation to stress or signaling. Several reports relate changes in glycosylated sterols levels with the plant response to abiotic stress, but the information about the role of these compounds in the response to biotic stress is scarce. In this work, we have studied the response to the necrotrophic fungus in an mutant that is severely impaired in steryl glycosides biosynthesis due to the inactivation of the two sterol glucosyltransferases (UGT80A2 and UGT80B1) reported in this plant. This mutant exhibits enhanced resistance against when compared to wild-type plants, which correlates with increased levels of jasmonic acid (JA) and up-regulation of two marker genes ( and ) of the ERF branch of the JA signaling pathway. Upon infection, the double mutant also accumulates higher levels of camalexin, the major phytoalexin, than wild-type plants. Camalexin accumulation correlates with enhanced transcript levels of several cytochrome P450 camalexin biosynthetic genes, as well as of their transcriptional regulators , , and , suggesting that the -induced accumulation of camalexin is coordinately regulated at the transcriptional level. After fungus infection, the expression of genes involved in the indole glucosinolate biosynthesis is also up-regulated at a higher degree in the mutant than in wild-type plants. Altogether, the results of this study show that glycosylated sterols play an important role in the regulation of response to infection and suggest that this occurs through signaling pathways involving the canonical stress-hormone JA and the tryptophan-derived secondary metabolites camalexin and possibly also indole glucosinolates.