Known interactors or regulators, such as CIPK8, CIPK23, CBL1, and CBL9 as well as other interactors identified in a large-scale membrane protein interaction screen were co-expressed with NiTrac1 in yeast cells. (A) Donor quenching response of NiTrac1 with vector as control. (B) and (C) Fluorescence response of NiTrac1 in CIPK23 and CBL9 coexpressing yeast, respectively. (D) The fluorescence response indicates that CIPK23, CBL1, At2g40540, and At5g41990 affect the conformation NiTrac1, whereas no detectable change is observed for CBL9, CIPK8, At1g71140, and At1g25510. Experiment performed as in Figure 1C. (A–C) Nitrate-induced ratio change (peak fluorescence intensity of Aphrodite excited at 505 nm over emission spectrum obtained with excitation at 428 nm). Data are normalized to KCl-treated control at 470 nm. An asterisk indicates a significant difference (p<0.05, t test) compared with the KNO3-treated control. Mean ± SD; n = 3.