CmFSI8/CmOFP13 gene encoding an OFP family protein controls fruit shape in melon (Cucumis melo L.).

Fruit shape is an important quality and yield trait in melon. Although some fruit shape-related QTLs have been reported in melon, the target genes and the underlying mechanism remain poorly understood. Here, we identified and characterized a gene controlling fruit shape from two melon inbred lines B8 and HP22. Genetic analysis suggests that the fruit shape was controlled by a single and incompletely dominant locus, designated CmFSI8/CmOFP13. The CmFSI8/CmOFP13 gene was finely mapped to a 53.7 kb interval on chromosome 8 based on BSA-seq and map-based cloning strategies. CmFSI8/CmOFP13 encodes an OVATE family protein (OFP) and is orthologous to AtOFP1 and SlOFP20. The transcription level of CmFSI8/CmOFP13 in the ovary of HP22 was significantly higher than that in B8. Sequence analysis showed that a 12.5 kb genomic variation with retrotransposon insertion identified in the promoter was responsible for elevating the expression of CmFSI8/CmOFP13, which ultimately caused the differences in fruit shape. Moreover, ectopic overexpression of CmFSI8/CmOFP13 in Arabidopsis led to multiple phenotypic changes, including kidney-shaped leaves and shortened siliques. Taken together, we have demonstrated the involvement of an OFP protein in regulating melon fruit shape, and understanding the molecular mechanism will enable us to better manipulate melon fruit shape in breeding.