CmERFⅠ-5 and CmERFⅤ-2 affect ethylene synthesis and sucrose accumulation in postharvest oriental melon fruit at low temperature

Postharvest low-temperature storage crucially affects ethylene-dependent fruit ripening and the sucrose accumulation of climacteric melon fruit; however, the molecular mechanism by which ethylene affects sugar content at low temperature remains unclear. Here, ‘High Sucrose’ (‘HS’) melon fruit were harvested at the initial stage of ethylene release (30 d after anthesis, DAA) and treated at different temperature (25 ℃, 10 ℃, and 4 ℃). The results revealed that both low temperature treatments had a lower sucrose content and sucrose percentage while also having a higher starch content, hexose level, vacuolar invertase (VINV) activity, and CmVINV2 expression in the melon fruit. Moreover, the ethylene production and CmACO1 (ACC oxidase 1) expression were lower at low temperature. Both low-temperature treatments positively and negatively regulated the expression of the ethylene response factors CmERFV-2 and CmERFI-5, respectively. We found that CmERFV-2 and CmERFI-5 could positively regulate the promoters of CmVINV2 and CmACO1, respectively. The agrobacterium-mediated transient transformation further verified that CmERFV-2 silencing and CmERFI-5 overexpression resulted in higher sucrose levels and produced more ethylene. In short, postharvest low-temperature treatments promoted CmERFV-2 expression and inhibited CmERFI-5 expression, which activated the transcription of downstream CmVINV2 and CmACO1, respectively, ultimately affecting sugar content and ethylene biosynthesis. The lower production of ethylene at low temperature reduced starch degradation, thereby affecting sugar accumulation in melon fruit. This study explained the cause for the lower sweetness of postharvest oriental melon fruit at low temperature and provided new insights into maintaining flavour quality at low temperature.