Impaired sterol glycosides biosynthesis induces resistance to Botrytis cinerea in the Arabidopsis mutant ugt80A2B1

Abstract

Free and glycosylated sterols are structural components of cell membranes that play a key role in regulating their biophysical properties and consequently different PM-associated processes like plant adaptation to biotic and abiotic stress, signalling or transport (Griebel and Zeier, 2010; Posé et al, 2009; Gamir et al, 2016). However, the specific role of glycosylated sterols in these processes is far from being understood. Arabidopsis contains two UDP-glucose sterol glycosyltransferases (UGT80A2 and UGT80B1) that catalyse the glycosylation of the hydroxyl group at C-3 position of free sterols to produce steryl glucosides (SG). To gain insight about the role of glycosylated sterols in the plant response to biotic stress, we investigated the response of the Arabidopsis double knockout mutant ugt80A2B1, impaired in SG biosynthesis (DeBolt et al. 2009), against the infection with the necrotrophic fungus Botrytis cinerea. The ugt80A2B1 mutant exhibits enhanced resistance against B. cinerea when compared to wild-type plants, and the resistance phenotype correlates with increased levels of jasmonic acid (JA) and enhanced expression of the JA-responsive genes PDF1.2 and PR4. Moreover, upon B. cinerea infection the ugt80A2B1 mutant also accumulates higher levels of camalexin than wild type plants. Consistent with this observation, the expression of several genes related to camalexin biosynthesis and that of the camalexin synthesis regulator genes AtMYB51 and AtWRKY33 is higher in the mutant than in wt plants after infection. Altogether, the results of this study show that glycosylated sterols play an important role in the regulation of Arabidopsis response to B. cinerea infection and suggest that this occurs through a signalling pathway involving the hormone JA and camalexin, the main Arabidopsis phytoalexin. The possible role of glucosinolates, secondary metabolites involved in plants defense, in this resistance response will also be discussed.