(A-C) Root growth of Col-0 and brr mutants (+/- BL). (D) The gene structure of BSK3. Arrows point to the positions of five identified BSK3 mutations. White boxes represent 5’ UTR and 3’ UTR. Gray boxes and lines represent exons and introns, respectively. Triangle represents the T-DNA insert, and the insertion is in the first intron in the 5’ UTR of BSK3. (E) Western blot analysis of BSK3-HA protein expression in two brr1 BSK3-HA lines. Thirty micrograms of total proteins were loaded. (F) Primary root length of Col-0, brr1, and brr1 BSK3-HA seedlings. Different letters above the bars indicate significant differences (P < 0.05). (G) RT-PCR analysis of BSK3 gene expression. ACTIN2-FW/ACTIN2-RV and BSK3-FW/BSK3-RV primers were used to amplify ACTIN2 (25 cycles) and BSK3 (40 cycles) transcripts, respectively. (H and I) Root growth of Col-0, bsk3-1/+, and bsk3-1 seedlings (+/- BL). (A-C and E-I) Seedlings were grown in the light for 7 days. Error bars represent SEM (n = 36–60). Scale bar = 0.5 cm.