Objective Genes and network that regulates the growing and ripening of bitter gourd fruits were studied.

Method Phenotype changes in length, diameter, cavity diameter, flesh thickness and fresh weight of the developing fruits of the advanced inbred line ‘ZK54’, Momordica charantia L., were investigated. Differentially expressed genes (DEGs) at different stages were determined by high-throughput transcriptome sequencing. GO functional annotations, KEGG pathway enrichment characteristics, gene profiles and expression trends were systematically analyzed. Genes associated with fruit expansion and ripening as well as the regulating network were identified.

Results As a bitter gourd plant grew, the fruits expanded in a slow-fast-slow pattern. At the slow expansion stage, DEGs related to the amino acid precursors in various organelles and ribosomal metabolism presented predominantly. At the early and late rapid expansion stages, the prevalent DEGs were associated with cell wall structure, hormone signal transduction, and coenzyme metabolism. At the maturation stage, fruits tended to contain DEGs largely involved in photosynthesis, pigment metabolism, hormone signal transduction, and antioxidant activity. There were 4 gene profiles identified to be significantly correlated with the phenotypes, and 20 genes with distinct expression patterns annotated to be associated with the expansion and ripening of the fruits. Genes of lipid transfer proteins, tubulins, aspartic proteases, and ubiquitin E3 ligases were also found to critically contribute to the complex regulatory network.

Conclusion The expansion of bitter gourd fruits followed the similar pattern like other horticultural crops. During the enlargement and maturation stages, the cells underwent distinctive phases of division and differentiation. The process required not only the roles played by the genes identified in this study but also the participation of some crucial genes in the network to facilitate the dynamic regulation function.