Plant specific protein that enhances G-box-binding factor (GBF) DNA binding activity. May function as a nuclear chaperone or lever and regulate the multimeric state of GBFs. May contribute to bZIP-mediated gene regulation. Is able to refold denatured rhodanese in vitro (PubMed:16117846, PubMed:25387999). Reduces DNA-binding activity of BZIP16, BZIP68 and GBF1 under non-reducing conditions through direct physical interaction. Acts as negative co-regulator in red and blue light-mediated hypocotyl elongation. Functions to promote hypocotyl elongation during the early stages of seedling development by regulating the repression effect by BZIP16 and the activation effect by BZIP68 and GBF1 on LHCB2.4 expression (PubMed:25387999). Enhances transcriptional activity of LBD18 in the EXP14 promoter. May act as a transcriptional coactivator of LBD18 (PubMed:24484953). Monomer, homodimer, homooligomer. Under non-reducing conditions, predominantly present in high molecular weight forms, but predominates in low molecular weight monomers under reducing conditions (PubMed:25387999). Interacts with BZIP16, BZIP68 and GBF1 (PubMed:25387999). Interacts with LBD18 (PubMed:24484953). Expressed in roots, leaves, stems and flowers. Belongs to the GIP1 family.