Mutations in CSU4 suppress cop1-6 in the dark. (A and B) Hypocotyl phenotypes and length of 4-d-old Col, cop1-6, and csu4 cop1-6 seedlings grown in the dark. Error bars represent SE (n ≥ 20). Letters above the bars indicate significant differences (P < 0.05) as determined by one-way ANOVA with Tukey’s post hoc analysis. (C and D) Cotyledon phenotypes and separation angle of 4-d-old Col, cop1-6, and csu4 cop1-6 seedlings grown in the dark. Error bars represent SE (n ≥ 30). Letters above the bars indicate significant differences (P < 0.05) as determined by one-way ANOVA with Tukey’s post hoc analysis. (E) Genomic complementation test. Phenotypes of Col, cop1-6, csu4-1 cop1-6, csu4-2 cop1-6, three independent CSU4pro:CSSU4 csu4-1 cop1-6, and three independent 35S:YFP-CSU4 csu4-2 cop1-6 transgenic lines grown in darkness for 4 d. The experiments were performed three times, with similar results. The graphs depict one of three experiments.