Sitosterol represses the expression of ProYUC8:GUS and DR5:GUS, and partially rescues the short root phenotype of cpi1-1. (A) Expression of ProYUC8:GUS treated with or without sitosterol. The images are representative of n = 3 independent experiments employing 9 to 30 seedlings per experiment; (B) Expression of DR5:GUS in WT and cpi1-1 seedlings treated with or without sitosterol. The images are representative of n = 3 independent experiments employing 14 to 30 seedlings per experiment; (C,D) Quantitative GUS activity assay of ProYUC8:GUS (C) and DR5:GUS (D) in 5-day-old seedlings. Data are shown as means ± SD of n = 3 independent experiments. * p < 0.05 (one-way ANOVA with Tukey’s test); (E,F) Phenotypes (E) and relative root length (F) of WT and cpi1-1 seedlings grown on MS medium supplemented with different concentrations of sitosterol. Data are shown as means ± SD of n = 3 experiments (employing 12 to 45 roots per experiment). * p < 0.05, *** p < 0.001 (Student’s t-test, one-tailed, two-sample equal variance). Bars = 100 μm in (A,B) and 1 mm in (E).