Search

(1) Background: Wax gourd is an economically important vegetable crop in many tropical and sub-tropical countries in Asia. Fruit color is an important fruit quality trait, but the genetic, biochemical basis and regulatory network of fruit color variation in wax gourd are rarely studied. (2) Methods: In this study, two wax gourd inbred lines with different pericarp colors were used as materials to conduct joint metabolomic and transcriptomic analyses on mature fruit pericarp: B214 with yellow and B227 with dark green color. (3) Results: It was found that the chlorophyll content in the pericarp of B214 was significantly lower than that of B227, consistent with the down-regulation of several genes involved in the chlorophyll biosynthesis pathway, including hemA, hemB, hemC, hemF, chlH, chlI, chlM, POR, and CAO. The 229 metabolites showed differential accumulation levels between B214 and B227, and 4 anthocyanins, 5 flavanones, 25 flavones, 25 flavone C-glycosides, 12 flavonols, and 3 isoflavones were identified. In particular, cyanidin 3-O-glucoside, an anthocyanin contributing to the coloration of dark color, showed higher accumulation in B227 than in B214, probably due to the higher expression of genes of F3′H and glucosyl transferases (GTs) in B227. Transcription factors such as MYBs and bHLHs showed differential expressions between the two lines including bHLH14, a homolog of Arabidopsis AtbHLH14 that had significantly higher expression in B227 than in B214. bHLH14 was located in a region where the pericarp color (pc) locus was mapped, suggesting it may be a candidate gene for the pc locus. (4) Conclusions: This work supports the association of chlorophyll and flavonoid synthesis in wax gourd fruit color variation and also provides a good foundation for understanding the regulatory network for wax gourd coloration. [ABSTRACT FROM AUTHOR]

The wax gourd (Benincasa hispida), the only species in the genus Benincasa, is an important crop native to Asia that has been widely planted for multi-purpose uses. The first wax gourd draft genome was published three years ago, but it was incomplete and highly-fragmented due to data and technical limitations. Herein, we report a new chromosome-level genome assembly and annotation of B. hispida. We generated 974.87 Mb of unitigs with N50 size of 2.43 Mb via a hybrid assembly strategy by using PacBio long reads and Illumina short reads. We then joined them into scaffolds with Hi-C data, resulting 1862 scaffolds with a total length of 975.62 Mb, and 94.92% of the length (926.05 Mb) is contained in the 12 largest scaffolds corresponding to the 12 chromosomes of B. hispida. We predicted 37,092 protein-coding genes, and 85.05% of them were functionally annotated. This chromosome-level reference genome provides significant improvement to the earlier version of draft genome and would be valuable resource for research and molecular breeding of the wax gourd., (© 2023. The Author(s).)