Triadimefon, a fungicidal triazole-type P450 inhibitor, induces brassinosteroid deficiency-like phenotypes in plants and binds to DWF4 protein in the brassinosteroid biosynthesis pathway

Abstract

Triadimefon (Bayleton), a widely used triazole-type fungicide, affects gibberellin (GA) biosynthesis and 14 alpha-demethylase in sterol biosynthesis. The present study revealed that the phenotype of Arabidopsis treated with triadimefon resembled that of a brassinosteroid (BR)-biosynthesis mutant, and that the phenotype was rescued by brassinolide (BL), the most active BR, partly rescued by GA, and fully rescued by the co-application of BL and GA, suggesting that triadimefon affects both BR and GA biosynthesis. The target sites of triadimefon were investigated using a rescue experiment, feeding triadimefon-treated Arabidopsis BR-biosynthesis intermediates, and a binding assay to expressed DWF4 protein, which is reported to be involved in the BR-biosynthesis pathway. The binding assay indicated that the dissociation constant for triadimefon was in good agreement with the activity in an in planta assay. In the triadimefon-treated Arabidopsis cells, the CPD gene in the BR-biosynthesis pathway was up-regulated, probably due to feedback regulation caused by BR deficiency. These results strongly suggest that triadimefon inhibits the reaction catalysed by DWF4 protein and induces BR deficiency in plants. As triadimefon treatment has proved to be beneficial to plants, this result suggests that BR-biosynthesis inhibitors can be applied to crops.

Genetic Variation in Plant CYP51s Confers Resistance against Voriconazole, a Novel Inhibitor of Brassinosteroid-Dependent Sterol Biosynthesis

“…To compare the potency of the identified compounds in affecting plant growth we decided to analyze their ability to inhibit hypocotyl elongation of cress, an assay frequently used to investigate BR action [21], [22], [35], [24], [36]. As shown in Figure 2B, voriconazole strongly reduced hypocotyl elongation of cress with significant effects detectable at a concentration of 30 nM.…”

“…However, their activities vary as they interfere with the biosynthesis of different metabolites important for plant development including BRs, gibberellins (GAs) and sterols, respectively [28], [39], [21], [22], [24], [36].…”

Relationship between brassinosteroids and genes controlling stomatal production in the Arabidopsis hypocotyl

“…Plants treated with 1 mM triadimefon, which inhibits biosynthesis of brassinosteroids and gibberellins (Buchenauer and Rohner, 1981;Asami et al, 2003), showed a small reduction in the number of stomata, with the exception of Col-0 (Table 1). This reduction was counteracted by the co-application of 0.5 mM epibrassinolide, confirming that this plant regulator promotes stomata formation in the hypocotyl (Table 1).…”

Cytochrome P450s in plant steroid hormone synthesis and metabolism

“…The triazole-type BR biosynthesis inhibitor, brassinazole, inhibits the BR C-22 hydroxylation step by binding to CYP90B1 protein (Asami et al 2001). Also the widely used triazole-type fungicide, Triadimefon, binds to CYP90B1 to suppress BR biosynthesis (Asami et al 2003). In rice CYP90B2 mutants exhibit a weak phneotype due to the presence of CYP724B1 that can also catalyse C-22 hydroxylation as described below (Sakamoto et al 2006).…”