Postharvest water loss is a critical factor that determines the quality and shelf life of fresh fruit. Cuticular wax constitutes a key barrier to reduce fruit water loss. Our previous study has shown that HJ (Citrus reticulata) has a significantly higher postharvest water loss rate than ZK (Poncirus trifoliata). Here, we investigated the fruit water loss rate of the HJ × ZK F₁ pseudo-testcross population in 2016 and 2019. QTL mapping for fruit water loss rate was performed by high-density genetic map and bulk segregant analysis, and QTL9 was identified to be associated with fruit water loss. The expression of NAC042 from QTL9 in ZK was 170-fold that in HJ. Heterologous expression in Arabidopsis showed that NAC042 could reduce the water loss of leaves by increasing the cuticular wax content (especially alkanes). Further expression analysis revealed that NAC042 could enhance the expression of many wax-related genes in Arabidopsis leaves, including AtKCS1, AtKCS2, AtKCS9, AtKCS20, AtCER1 and AtCER3. Therefore, NAC042 might be involved in fruit cuticular wax synthesis to reduce fruit water loss. The findings provide new insights into the regulation of cuticular wax and fruit water loss as well as valuable information for breeding of citrus with better storability.

Sesquiterpene valencene is dominant in flavedo tissues of sweet oranges and imparts a unique woody aroma. However, the interaction between the biosynthetic pathways of valencene and other nutritional compounds is less studied. Sesquiterpenoids were significantly accumulated in a previously reported glossy mutant of orange (MT) than the wild type (WT), especially valencene and caryophyllene. In addition, we identified several other pathways with variations at both the transcriptional and metabolic levels in MT. It's interesting to found those up-regulated metabolites in MT, such as eukaryotic lipids, kaempferol and proline also showed strong positive correlation with valencene along with fruit maturation while those down-regulated metabolites, such as phenylpropanoid coumarins and most of the modified flavonoids exhibited negative correlation. We then categorized these shifted pathways into the 'sesquitepenoid-identical shunt' and the sesquitepenoid-opposite shunt' and confirmed the classification result at transcriptional level. Our results provide important insights into the connections between various fruit quality-related properties.