Ferulic acid enhances chilling tolerance in tomato fruit by up-regulating the gene expression of CBF transcriptional pathway in MAPK3-dependent manner

Ferulic acid (FA, 4-hydroxy-3-methoxycinnamic acid) is a phenolic acid derivative of cinnamic acid and plays pleiotropic roles in biotic and abiotic stress response in plants. However, the involvements of FA in chilling stress tolerance and the molecular mechanisms related to mitogen-activated protein kinase (MAPK) in tomato fruit are still elusive. In this study, the effect of exogenous FA on chilling resistance of tomato fruit was investigated. In addition, CRISPR/Cas9-mediated slmapk3 mutants were used to investigate the relationship between FA and SlMAPK3 under chilling stress. The results showed that low temperature (4 ℃) induced increase of FA content and FA synthesis related genes (SlPAL5, SlC3H and SlCOMT) expression. In addition, exogenous FA reduced the severity of cold injury, up-regulated the expressions of SlMAPK3, SlCBF1 and SlICE1, and promoted the accumulation of proline and soluble protein content. However, knockout of SlMAPK3 reduced the chilling tolerance of tomato fruit and inhibited the activities of antioxidant enzymes (APX, POD, SOD and CAT) but induced the accumulation of H2O2. In the condition of low temperature (4 ℃), there was a high correlation between SlMAPK3 and FA synthesis related genes (SlPAL5, SlC3H, SlC4H and SlCOMT) in control fruit. However, knockout of SlMAPK3 inhibited the content of FA and the expression of those genes compared with the control, which suggested a close relationship between SlMAPK3 and FA. Specifically, the effects of FA on osmotic regulatory substance and antioxidant enzyme system as well as the gene expression of CBF (C-repeat binding transcription factor) pathway were reduced after knockout of SlMAPK3. These results unveil a function of FA in tomato fruit positively resistance to chilling stress by up-regulating the gene expression of CBF transcriptional pathway in MAPK3-dependent manner.