A ‘golden’ SNP in CmOr governs the fruit flesh color of melon (Cucumis melo)

Summary The fleshcolor of Cucumis melo( melon) is genetically determined, and can be white, light green or orange, with β– carotenebeing the predominant pigment. We associated carotenoid accumulation in melonfruit fleshwith polymorphism within CmOr, a homolog of the cauliflower BoOr gene, and identified CmOr as the previously described gf locus in melon. CmOr was found to co-segregate with fruit fleshcolor, and presented two haplotypes(alleles) in a broad germplasm collection, one being associated with orange fleshand the second being associated with either white or green flesh. Allelic variation of CmOr does not affect its transcription or protein level. The variation also does not affect its plastid subcellular localization. Among the identified single nucleotide polymorphisms (SNPs) between CmOr alleles in orange versus green/white- fleshfruit, a single SNP causes a change of an evolutionarily highly conserved arginine to histidine in the CmOr protein. Functional analysis of CmOr haplotypesin an Arabidopsis callus system confirmed the ability of the CmOr orange haplotypeto induce β– caroteneaccumulation. Site-directed mutagenesis of the CmOr green/white haplotypeto change the CmOR arginine to histidine triggered β– caroteneaccumulation. The identification of the ‘golden’ SNP in CmOr, which is responsible for the non-orange and orange melonfruit phenotypes, provides new tools for studying the Or mechanism of action, and suggests genome editingof the Or gene for nutritional biofortificationof crops.