ZTL and LKP2, but not FKF1, are required for the accumulation of CIB1 protein in response to blue light. (A) Immunoblot showing the lack of blue-light–dependent CIB1 accumulation in two different ztl mutant alleles. The transgenic plants expressing the 35S::Myc–CIB1 transgene in the wild-type (CIB1/WT) and ztl-3 (CIB1/ztl-3) and ztl-21 (CIB1/ztl-21) mutant backgrounds were grown in LD (16hL/8hD) for 3 wk, transferred to continuous red light (20 µmol⋅m−2⋅s−1) for 16 h, and then transferred to blue light (35 µmol⋅m−2⋅s−1) for the indicated time before sample collection. Immunoblot was probed with the anti-Myc antibody, stripped, and reprobed with the anti-CRY1 antibody as the loading control. (B) Immunoblots showing levels of the CIB1 protein in different genetic backgrounds treated with blue light in the absence or presence of the proteasome inhibitor MG132. The transgenic plants expressing the 35S::Myc–CIB1 transgene in the wild-type (CIB1/WT) or ztl (CIB1/ztl-3), lkp2 (CIB1/lkp2), or fkf1 (CIB1/fkf1) mutants were grown in LD (16hL/8hD) for 3 wk and transferred to blue light (35 µmol⋅m−2⋅s−1) for 16 h. Leaves were excised, incubated in MG132 (50 µmol/L) or mock solution (0.1% DMSO) in blue light for 3 h, and the samples were analyzed by immunoblot probed with the anti-Myc antibody. A nonspecific band (NS) is included as the loading control. Two independent transgenic lines of each genotype were tested and shown (Lines). (C) Immunoblots showing levels of the CIB1 protein in different genetic backgrounds treated with red light in the absence or presence of the proteasome inhibitor MG132. The transgenic plants expressing the 35S::Myc–CIB1 transgene in wild-type (WT) or ztl-3, lkp2, or fkf1 mutants were grown in LD for 3 wk and transferred to red light (20 µmol⋅m−2⋅s−1) for 16 h. Leaves were excised, incubated in MG132 (50 µmol/L) or mock solution (0.1% DMSO) under red light for 3 h, and analyzed by immunoblot probed with the anti-Myc antibody. A nonspecific band (NS) is included as the loading control. Two independent transgenic lines of each genotype were tested and shown (Lines).