Citrus VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1) interacts with CuFT1 and CuFT3, affecting flowering in transgenic Arabidopsis

•The protein-protein interactions between CuVOZ1 (Citrus unshiu VASCULAR PLANT ONE-ZINC FINGER1) and CuFT1 (Citrus unshiu FLOWERING LOCUS T) and between CuVOZ1 and CuFT3 were confirmed via the Y2H system.•The nature of binding in the CuVOZ1―CuFT1, CuVOZ1―CuFT3, and CuVOZ1―AtFT complexes was predicted with a docking simulation.•The 35SΩ:CuVOZ1 transgenic Arabidopsis suggested that CuVOZ1 might act as one of the triggers for early flowering and might also be involved in the elongation and branching of the inflorescence. Understanding the flowering process is essential for developing methods to shorten the breeding period and regulate the yield of tree fruits, such as Satsuma mandarin (Citrus unshiu Marc.). In the flowering network system in Arabidopsis, FLOWERING LOCUS T (FT) acts as a transmissible floral inducer. In this study, a citrus ortholog of the transcription factor (TF) VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1)-like gene, CuVOZ1, and two FT-like genes, CuFT1 and CuFT3, were isolated from the Satsuma mandarin ‘Aoshima’. Protein-protein interaction between CuVOZ1 and CuFTs was confirmed in vitro with a yeast two-hybrid (Y2H) system. N-terminal 400 amino acids of CuVOZ1, consisting of three motifs, namely, domain of unknown function 4749 (DUF4749), no apical meristem (NAM), and a zinc coordination motif, were assumed to be involved in the CuVOZ1–CuFT1 and CuVOZ1–CuFT3 complexes. Docking simulation suggested that only the zinc coordination motif of CuVOZ1 was possibly involved in the CuVOZ1–CuFT3 interaction and that the phosphatidylethanolamine-binding protein (PBP) motif in exon 4 of CuFTs was predicted to be crucial for the interaction between CuVOZ1 and CuFTs. The distance between the amino acid residues involved in docking was predicted to be from 2.69 to 3.37 Å, suggesting that the forces between CuVOZ1 and CuFTs in the CuVOZ1–CuFT complexes were weak Van der Waals forces. Constitutive expression of CuVOZ1 in Arabidopsis affected the flowering time, plant size, morphology of inflorescence, number of flowers and siliques, and formation of flower buds on the elongated stem. It was suggested that CuVOZ1 might act as a trigger for early flowering and might be involved in the elongation and branching of the inflorescence. The CuVOZ1–CuFT complexes might regulate cellular proliferation and the formation of new tissues and affect both vegetative and reproductive development.