Transcription factor Constans-like 4 may regulate tomato fruit ripening by interacting with abscisic acid and ethylene signaling

Phytohormones are vital for tomato ripening, and abscisic acid (ABA) is speculated to induce ethylene biosynthesis at the initiate of tomato fruit ripening; however, its interaction sites remain unclear. In the present study, Constans-like 4 (SlCOL4), a CO/COL transcription factor, was cloned from tomato fruit. Amino acid sequence and subcellular location analysis proved that SlCOL4 was a typical transcription factor of the COL family. Gene expression analysis showed SlCOL4 expressed in different tissues of tomato plants and its transcription abundance declined at the onset of fruit ripening, coincidentally it was found to be down-regulated in ABA-treated tomato fruit and responded to exogenous ABA within 6 h after treatment. Meanwhile, yeast one-hybrid and dual-luciferase analysis showed that the ABA response factor SlAREB1 inhibited the transcription of SlCOL4, indicating it was directly regulated by ABA at the mature green stage of tomato fruit. In addition, the pericarp color turned red faster than that of control fruit, and the key ethylene biosynthesis genes, ACS2, ACS4, and ACO1, were up-regulated in SlCOL4 silenced tomato fruit, suggesting that SlCOL4 may be a negative regulator of ripening. Furthermore, several genes associated with the ethylene signaling pathway were identified downstream of SlCOL4 by chromatin immunoprecipitation sequencing (ChIP-Seq) analysis. Overall, the transcription factor SlCOL4 may interact with ABA and ethylene signals and negatively regulate tomato fruit ripening. The results in this study provide new insights for elucidating the molecular mechanism of ABA-ethylene interaction in regulating tomato fruit ripening, and provide references for further research on the role of COLs transcription factors in tomato fruit ripening as well.