BR and BZR1 play critical roles in sugar- and TOR-induced BAM1 expression. A, Sucrose failed to induce BAM1 expression in det2-1 and bzr-h. Seedlings of Col-0, det2-1, and bzr-h were grown on 1/2 MS medium with or without 1% sucrose under a 12-h light/12-h dark photoperiod with 10-µM m⁻² s⁻¹ light for 10 days. RT-qPCR analysis BAM1 expression in wild-type and mutant plant under different conditions. PP2A was used as an internal control. Error bars indicate sd of four biological repeats. Different letters above bars indicate statistically significant differences between samples (two-way ANOVA followed by uncorrected Fisher’s LSD multiple comparisons test, P < 0.05). B and C, The gain-of-function mutant bzr1-1D partially suppressed the AZD8055-inhibited BAM1 expression. Seedlings of ProBAM1::GFP and ProBAM1::GFP/bzr1-1D transgenic plants were grown on the 1/2 MS medium with or without 1 µM AZD8055 under 12-h light/12-h dark photoperiod with 10-µM m⁻² s⁻¹ light condition for 10 days. GFP signal intensity was analyzed using ImageJ software. Error bars indicate sd (n = 10). GFP are in green, PI-marked cell outlines are in purple. Scale bars in confocal images represent 50 μm. Different letters above bars indicate statistically significant differences between samples (two-way ANOVA followed by uncorrected Fisher’s LSD multiple comparisons test, P < 0.05). D and E, Quantification of guard cell starch granules (D) and stomatal apertures (E) in the intact leaves of Col-0, bzr-h and bzr1-1D at the indicated time points. Seedlings of wild-type Col-0, bzr-h, and bzr1-1D were grown on the 1/2 MS medium with or without 1% sucrose under a 12-h light/12-h dark photoperiod with 10-µM m⁻² s⁻¹ light condition for 10 days. F and G, The bzr1-1D mutant had no significant effects on TOR-mediated guard cell starch metabolism (F) and stomatal opening (G). Seedlings of es-tor and es-tor/bzr1-1D were grown on the 1/2 MS medium containing 1% sucrose under a 12-h light/12-h dark photoperiod with 100-µM m⁻² s⁻¹ light condition for 7 days, transferred to the medium containing mock solution or 10- µM Figure 4 (Continued) estradiol to grow for another 3 days and then harvested at the indicated time points and immediately fixed in buffer for starch quantification (F) or used to directly measure the stomatal apertures (G). H and I, Quantification of guard cell starch granules (H) and stomatal apertures (I) in the intact leaves of Col-0 and bzr1-1D with or without AZD8055 treatment. Seedlings of Col-0 and bzr1-1D were grown on the 1/2 MS medium containing 1% sucrose under a 12-h light/12-h dark photoperiod with 100-µM m⁻² s⁻¹ light condition for 10 days, transferred to the medium containing mock solution or 2 µM AZD8055 to grow for 24 h, and harvested at the indicated time points. Starch granules (H) and stomatal apertures (I) were then measured. EoN means the end of light, light 1 h means the white light illumination for 1 h after the EoN. The starch granules in guard cells or the ratio of stomatal aperture width to length from at least 100 guard cells from 10 to 15 leaves of 8 different plants were measured using ImageJ software. Every measurement of stomatal starch granule area or stomatal aperture was labeled as a dot on box plot. The box extends from the 25th to 75th percentiles and plots each individual value as a point superimposed on the graph. The line in the middle of the box is plotted at the median. Different letters above the bars indicate statistically significant differences between samples (two-way ANOVA followed by Tukey’s multiple comparisons test, P < 0.05).