Abstract
The plant steroid hormone brassinosteroids (BRs) are important signal mediators that regulate broad aspects of plant growth and development. With the discovery of brassinoazole (Brz), the first specific inhibitor of BR biosynthesis, several triazole-type BR biosynthesis inhibitors have been developed. In this article, we report that fenarimol (FM), a pyrimidine-type fungicide, exhibits potent inhibitory activity against BR biosynthesis. FM induces dwarfism and the open cotyledon phenotype of Arabidopsis seedlings in the dark. The IC50 value for FM to inhibit stem elongation of Arabidopsis seedlings grown in the dark was approximately 1.8 ± 0.2 μM. FM-induced dwarfism of Arabidopsis seedlings could be restored by brassinolide (BL) but not by gibberellin (GA). Assessment of the target site of FM in BR biosynthesis by feeding BR biosynthesis intermediates indicated that FM interferes with the side chain hydroxylation of BR biosynthesis from campestanol to teasterone. Determination of the binding affinity of FM to purified recombinant CYP90D1 indicated that FM induced a typical type II binding spectrum with a Kd value of approximately 0.79 μM. Quantitative real-time PCR analysis of the expression level of the BR responsive gene in Arabidopsis seedlings indicated that FM induces the BR deficiency in Arabidopsis.
Highlights
Brassinosteroids (BRs) are plant-specific polyhydroxysteroids that are structurally similar to cholesterol-derived animal steroid hormones and the insect molting hormones ecdysteroids.The identification of BR-deficient and BR-insensitive mutants provided conclusive evidence that BRs are potent growth-promoting plant hormones
We found that fenarimol (FM, the structure is shown in Figure 2), a fungicide used worldwide that acts as a potent inhibitor of ergosterol biosynthesis, induced phenocopy of BR-deficient mutants with short hypocotyl and open cotyledons [24]
We use yucaizol: {1-[2-(4-Chlorophenyl)-4-(2-propoxyphenoxymethyl)[1,3]dioxolan-2-ylmethyl]-1H-[1,2,4] triazole}, a potent inhibitor of BR biosynthesis developed in our laboratory [13,14,15,16,26], as a positive control
Summary
Brassinosteroids (BRs) are plant-specific polyhydroxysteroids that are structurally similar to cholesterol-derived animal steroid hormones and the insect molting hormones ecdysteroids. In which grain yields were significantly increased by growing lodging-resistant semi-dwarf varieties of wheat and rice [11] In this context, reducing BR levels in plant tissues using chemicals is one feasible method to facilitate the improvement of crop yields. The establishment of the biosynthetic pathways (Figure 1) [17] and functional analysis of BR biosynthesis enzymes provided important information for the rational development of BR biosynthesis inhibitors. Heterocyclic compounds bind to the lipophilic regions of the protein and simultaneously interact with the prosthetic heme iron [23] Based on these observations, we conducted a chemical screening of new BR biosynthesis inhibitors among the 14-α demethylase (CYP51)-inhibiting fungicides. Because the mechanisms underlying the action of FM on BR biosynthesis have not yet been elucidated, we report the biochemical and physiological assessments of the mechanism of action of FM on BR biosynthesis
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