Reduction of Tomato-Plant Chilling Tolerance by CRISPR-Cas9-Mediated SICBF1 Mutagenesis

Chilling stress is the main constraint in tomato (Solanum lycopersicum) production, as this is a chilling-sensitive horticultural crop. The highly conserved C-repeat binding factors (CBFs) are cold-response-system components found in many species. In this study, we generated slcbfl mutants using the CRISPR-Cas9 system and investigated the role of SICBF1 in tomato-plant chilling tolerances. The slcbfl mutants exhibited more severe chilling-injury symptoms with higher electrolyte leakage and malondialdehyde levels than wild-type (WT) plants. Additionally, slcbfl mutants showed lower proline and protein contents and higher hydrogen peroxide contents and activities of antioxidant enzymes than WT plants. Knockout of SICBF1 significantly increased indole acetic acid contents but decreased methyl jasmonate, abscisic acid, and zeatin riboside contents. The reduced chilling tolerance of the slcbfl mutants was further reflected by the down-regulation of CBF-related genes. These results contribute to a better understanding of the molecular basis underlying SICBF1 mediation of tomato chilling sensitivity.