EjCML19 and EjWRKY7 synergistically function in calcium chloride-alleviated chilling injury of loquat fruit

The regulatory function of calcium chloride (CaCl2) in chilling injury (CI) has been proven in loquat fruit. Nevertheless, its physiological and molecular mechanisms are relatively still unclear. In this work, the CaCl2 treatment reduced the CI in loquat fruit, with a lower internal browning index, firmness, and higher extractable juice in comparison with the control. Moreover, CaCl2 application impacted the contents of phenolic acids in cold-stored loquat fruit. Transcriptome analysis identified a total of 5416 differently expressed genes (DEGs), and the key DEGs were enriched in many metabolic pathways, including phenylpropanoid biosynthesis, biosynthesis of secondary metabolites, plant hormone signal transduction, phenylalanine metabolism, membrane lipid degradation, starch and sucrose metabolism. The fold change and the expression intensity of EjCML19 and EjWRKY7 in loquat fruit during cold storage were higher, and EjCML19 could interact with EjWRKY7 in yeast cells. The qRT-PCR analysis found that CaCl2 induced the transcription of EjCML19 and EjWRKY7 but down-regulated browning-related genes EjRBOHC and EjPPO in loquat fruit. The genes (EjRBOHC and EjPPO) contain W-box elements in their promoters, implying that they might be target genes of EjWRKY7. Therefore, EjCML19 and EjWRKY7 were selected and cloned from loquat fruit to explore their regulatory role of EjRBOHC and EjPPO. Further investigation revealed that EjWRKY7 negatively modulated the expression of EjRBOHC and EjPPO by binding to their promoters. EjCML19 enhanced EjWRKY7-mediated transcriptional repression of EjPPO in loquat fruit under cold stress. Taken together, EjCML19 and EjWRKY7 synergistically regulated the transcription of browning-related genes, which functioned a positive role in CaCl2-alleviated chilling injury in loquat fruit under refrigeration.