Fenoxycarb, a carbamate insect growth regulator, inhibits brassinosteroid action.

Brassinosteroids (BRs) are steroid hormones that regulate plant growth, development, and stress resistance. In this study, we evaluated the effect of agrochemicals on dark-induced hypocotyl elongation, which is regulated by BRs, to identify novel chemicals that regulate BR action. We found that the juvenile hormone agonist fenoxycarb inhibited dark-induced hypocotyl elongation in Arabidopsis. Treatment with the same class of juvenile hormone agonist, pyriproxyfen, did not affect hypocotyl elongation. Co-treatment with fenoxycarb and BR partly canceled the fenoxycarb-induced hypocotyl suppression. In addition, gene expression analysis revealed that fenoxycarb altered the BR-responsive gene expression. These results indicate that fenoxycarb is a BR action inhibitor.