Calcium Deficiency Leads to Fruit Blackheart Formation by Disrupting Glycometabolism and Phenylpropanoid Metabolism in Wax Gourd

Wax gourd (Benincasa hispida (Thunb.) Cogn) is a vegetable crop with a long storage period; however, blackheart disorder seriously compromises its storability and economic value. This study delves into the spatial-temporal process of blackheart disorder in wax gourd fruit at the physiological, transcriptional, and metabolic levels. The findings revealed decreased concentrations of total calcium (Ca), Ca-pectinate, and chelate-soluble pectin (CSP), and increased levels of total phenolics, flavonoids, and lignin during the development of blackheart disorder. These changes in physiological indicators in blackheart fruit were regulated by the expression of relevant genes, the accumulation of key metabolites, and increased enzyme activities in the glycometabolism and phenylpropane metabolism pathways. Moreover, transcriptome analysis revealed significant suppression in the expression of Ca channel and transport-related genes in blackheart fruit. Finally, there was a pronounced correlation between CSP, Ca-pectinate, phenolic acid, flavonoids, and monosaccharides. Weighted gene co-expression network analysis identified several transcription factors related to blackheart development were identified. Importantly, it has been discovered for the first time that the development of blackheart disorder in wax gourd results from pectin degradation and metabolic disturbance caused by Ca deficiency. These findings lay a theoretical foundation for devising strategies to manage and control blackheart in wax gourds.