Crosstalk between calcium and melatonin affects postharvest physiological deterioration and quality loss in cassava

Rapid postharvest physiological deterioration largely reduces the quality and marketability of cassava. The molecular mechanism underlying cassava postharvest physiological deterioration and quality loss is largely unknown. The present study aimed to investigate the role of calcium and its relationship with melatonin in cassava postharvest physiological deterioration. Transcriptomic analyses indicate that most of the calcium ion (Ca2+) sensor genes are upregulated in cassava tuberous roots at different postharvest stages. Exogenous CaCl2 reduces postharvest physiological deterioration, increases the endogenous levels of Ca2+ and melatonin, reduces the degradation of ascorbic acid and starch, and induces the expression of genes related to melatonin biosynthesis after harvest. These effects are reversed by the exogenous application of a Ca2+ chelator (EGTA). Exogenous melatonin also increases endogenous melatonin levels and reduces ascorbic acid and starch degradation during postharvest physiological deterioration but do not affect endogenous Ca2+ content. Together, these findings demonstrate that calcium-induced activation of melatonin biosynthesis plays a role in reducing postharvest physiological deterioration and quality loss in cassava. Additionally, pretreatment with EGTA arrests the melatonin-induced reduction of postharvest physiological deterioration, suggesting the possible crosstalk between melatonin and calcium during postharvest physiological deterioration.