CaCl2 promoted phenolics accumulation via the CmCAMTA4-mediated transcriptional activation of phenylpropane pathway and energy metabolism in fresh-cut cantaloupe

Abstract

Phenolics are secondary metabolites in plants. Calcium chloride (CaCl2) application could promote phenolics accumulation whereas the molecular mechanism remains uncertain. In this study, CaCl2 treatment reinforced the increase of individual phenolic acid content, PAL, C4H and 4CL activities and activated related expressions of CmPAL1, CmPAL2, CmPAL3, CmC4H1, CmC4H2, CmC4H3, Cm4CL1 and Cm4CL2 in fresh-cut cantaloupe. The total phenolics, total flavonoids content and antioxidant capacity in CaCl2-treated fresh-cut cantaloupe were 39.53%, 33.33% and 23.08% higher than those in control fruit after 24 h of storage, respectively. In the meantime, CaCl2 application elevated of H+-ATPase, Ca2+-ATPase, SDH, CCO activities and elicited the transcription of CmH+-ATPase4, CmCa2+-ATPase2, CmSDH5 and CmCCO6 genes in fresh-cut cantaloupe. Moreover, CmCAMTA4, an up-regulated calmodulin-binding transcription activator (CAMTA) induced by CaCl2 was identified in fresh-cut cantaloupe. Further study suggested that CmCAMTA4 could bind the CG-box in the promoter region of CmPAL3, Cm4CL1 and CmCCO6 to activate their transcription. In summary, these findings indicated that CaCl2 treatment could activate the transcription of CmPAL3, Cm4CL1 and CmCCO6 mediated by CmCAMTA4, which stimulated the phenylpropane pathway and maintained higher energy status, thus facilitating the biosynthesis of phenolics in fresh-cut cantaloupe during storage.