Figure 5: TOPLESS is required for BR responses.

(a) The BZR1 transcriptional repression activity is compromised in tpl;tpr1;tpr4. Total RNA were extracted from etiolated seedlings grown on the medium containing 2 μM PPZ. The relative gene expression levels were determined by qRT–PCR. Numbers indicate the ratios of expression levels (bzr1-1D/Col-0 or bzr1-1D;tpl;tpr1;tpr4 / tpl;tpr1;tpr4). Error bars indicate the s.d. (n=3). (b) The tpl;tpr1;tpr4 triple mutant is less sensitive to BR. Seedlings were grown for 5 days on the medium containing either mock or 1,000 nM BL. Numbers indicate ratio of hypocotyl lengths (BL-treated/mock-treated). Error bars indicate the s.d. (n=10 plants) and **P<0.01 by Student’s t-test. Scale bar, 5 mm. (c) The tpl;tpr1;tpr4 triple mutation suppresses the long hypocotyl phenotype of bzr1-1D. Seedlings were grown on the medium containing 2 μM PPZ for 6 days in the dark. Error bars indicate the s.d. (n=10 plants). n.s., not significant and **P<0.01 by Student’s t-test. Scale bar, 5 mm. (d) Scatter plot of fresh weight measurements of 3-week-old plants grown on the medium containing 2 μM PPZ. This experiment was repeated with similar results. **P<0.01 by Student’s t-test (n=10 plants). (e) TPL fusion at the C terminus restores the transcriptional repression activity of bzr1-1DmEAR. Relative expression fold changes of CPD and DWF4 were determined by qRT–PCR in Arabidopsis plants transformed with the indicated constructs, compared with wild type (Col-0). Error bars indicate the s.e. (n=4). (f) TPL fusion restores the activity of bzr1-1DmEAR in promoting hypocotyl elongation. Seedlings were grown in the dark on the medium containing 1 μM BRZ for 5 days. Error bars indicate the s.e. (n=10).