Fine Mapping and Identification of the Candidate Gene BFS for Fruit Shape in Wax Gourd (Benincasa Hispida)

Abstract Fruit shape is an important agronomic trait in wax gourds [Benincasa hispida (Thunb) Cogn.]. However, the candidate genes for this important trait, and their genetic mechanisms, remain unknown. In this study, we identified a candidate gene for fruit shape in wax gourds using a next-generation sequencing-based bulked segregant analysis in F2 populations derived from a cross between GX-71 (long cylindrical fruit, FSI = 4.56) and MY-1 (round fruit, FSI = 1.06) genotypes. According to bulked segregant analysis, the candidate gene is located in the 17.18 Mb region on chromosome 2, and the kompetitive allele specific polymerase chain reaction (KASP) marker was used to reduce it to the 19.6 Kb region. There is only one gene in the corresponding region of the reference genome, Bch02G016830 (designated BFS). We sequenced BFS in six wax gourd varieties with different fruit shapes. Sequence analysis showed that there were two non-synonymous mutations in the spherical wax gourd and one non-synonymous mutation in the cylindrical wax gourd. Quantitative real‑time polymerase chain reaction (qRT-PCR) analysis showed that the expression of BFS in round fruits was significantly higher than in long cylindrical fruits at the ovary formation stage. Therefore, BFS is a candidate gene for determination of the fruit shape of wax gourds. The predicted protein encoded by the BFS gene belongs to the IQD protein family, which have the structural characteristics of scaffold proteins and coordinate Ca2+ CaM signaling from the membrane to the nucleus. The BFS gene can assist with the breeding of new varieties that possess ideal fruit shapes.