EjCaM7 and EjCAMTA3 synergistically alleviate chilling-induced lignification in loquat fruit by repressing the expression of lignin biosynthesis genes

Flesh lignification is a typical chilling injury (CI) symptom of loquat fruit during cold storage. Calcium chloride (CaCl2) could enhance chilling tolerance in loquat fruit, but the molecular mechanism is still not illuminated. In this study, CaCl2 treatment could decrease the activities and genes expression of peroxidase (POD) laccase (LAC), and inhibit the increase in firmness and lignin accumulation, thereby alleviating chilling-induced lignification in loquat fruit. Additionally, CaCl2 enhanced the calmodulin (CaM) content, free Ca2+ distribution, EjCaM7, and CaM binding transcription activator 3 (EjCAMTA3) expression in loquat fruit during cold storage, indicating Ca2+/CaM-CAMTA might be played a key role in response to cold stress. Moreover, the EjCAMTA3 and EjCaM7 proteins were identified and characterized from loquat fruit. EjCAMTA3 bound to the CG-box in EjPOD64 and EjLAC12-like promoters to repress their transcription. Further analysis revealed that EjCaM7 interacted with EjCAMTA3 in a Ca2+-dependent manner, and this interaction enhanced the EjCAMTA3-mediated transcriptional repression of EjPOD64 and EjLAC12-like genes. Taken together, these findings suggested that CaCl2 treatment alleviates chilling-induced lignification in loquat fruit, which probably via the synergistic role of EjCaM7 and EjCAMTA3 in the modulation of EjPOD64 and EjLAC12-like genes expression, leading to the repression of lignin polymerization.