Classic myrosinase‐dependent degradation of indole glucosinolate attenuates fumonisin B1‐induced programmed cell death in Arabidopsis

Summary The mycotoxin fumonisin B1 (FB1) causes the accumulation of reactive oxygen species (ROS) which then leads to programmed cell death (PCD) in Arabidopsis. In the process of studying FB1-induced biosynthesis of glucosinolates, we found that indole glucosinolate (IGS) is involved in attenuating FB1-induced PCD. Treatment with FB1 elevates the expression of genes related to the biosynthesis of camalexin and IGS. Mutants deficient in aliphatic glucosinolate (AGS) or camalexin biosynthesis display similar lesions to Col-0 upon FB1 infiltration; however, the cyp79B2 cyp79B3 double mutant, which lacks induction of both IGS and camalexin, displays more severe lesions. Based on the fact that the classic myrosinase β-thioglucoside glucohydrolase (TGG)-deficient double mutant tgg1 tgg2, rather than atypical myrosinase-deficient mutant pen2-2, is more sensitive to FB1 than Col-0, and the elevated expression of TGG1, but not of PEN2, correlates with the decrease in IGS, we conclude that TGG-dependent IGS hydrolysis is involved in FB1-induced PCD. Indole-3-acetonitrile (IAN) and indole-3-carbinol (I3C), the common derivatives of IGS, were used in feeding experiments, and this rescued the severe cell death phenotype, which is associated with reduced accumulation of ROS as well as increased activity of antioxidant enzymes and ROS-scavenging ability. Despite the involvement of indole-3-acetic acid (IAA) in restricting FB1-induced PCD, feeding of IAN and I3C attenuated FB1-induced PCD in the IAA receptor mutant tir1-1 just as in Col-0. Taken together, our results indicate that TGG-catalyzed breakdown products of IGS decrease the accumulation of ROS by their antioxidant behavior, and attenuate FB1 induced PCD in an IAA-independent way.