Identification of QTLs Associated with Iron Uptake and Carotenoid Accumulation in Melon (Cucumis melo)

Iron is an important nutrient for plants and plant consuming animals and humans. An increased understanding of Fe uptake by plants could lead to potential strategies for biofortification. The C940-fe melon line ( fefe) does not induce normal Fe uptake responses, but the fefe gene is unknown. In this study, an F₂ mapping population was constructed using C940-fe, an orange fleshed cantaloupe-type melon and an exotic green fleshed melon PI 435288 (snake melon), to identify the genomic regions associated with fefe gene and fruit quality traits of melon. 

 Field grown plants were scored for fefe based on its distinct chlorotic phenotype. Beta-carotene was scored by color, and was grouped into six categories. A total of 633 SSR (genomic + EST) markers were tested, and 90 polymorphic markers were used to genotype 259 F₂ plants (125 in 2010 and 134 in 2011).

Current genetic map covers 1351.5 cM with an average of 21.8 cM between markers. With the current map, at least 10 QTLs associated with various fruit quality traits including fruit length, width, shape and fruit thickness were identified. Using interval analysis, fefe trait was mapped to single locus. Combined with comparative genomics and RNA-seq data, this allowed us to identify candidate genes for fefe. Sequence analysis of known Fe uptake genes resulted in no predicted functional differences between wild-type and fefe plants. These results suggest that fefe is a new gene that regulates iron uptake responses. Candidate genes will be tested for sequence differences between fefe and snake melon.