Abstract
In this study, a single recessive gene (designated w0) was identified to control the white immature fruit color. Genetic mapping with simple sequence repeats (SSR) markers located the w0 gene in the distal region of cucumber chromosome 3 (Chr.3). Fine mapping was then conducted using the method of draft genome scaffold-assisted chromosome walking with 7304 F2 individuals, which allowed for the assignment of the gene locus to a 100.3 kb genomic DNA region with two flanking markers, Q138 and Q193. Thirteen candidate genes were predicted in the 100.3 kb region. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that the expression of the Csa3G904140 gene, which encodes a two-component response regulator-like protein, was much higher in the immature fruit skin of the green parental line (Q1) than in the white parental line (H4). A coding sequence analysis suggested that a single-base insertion occurred at the ninth exon, resulting in a frameshift mutation in Csa3G904140 of H4, and the mutation was consistent with the phenotype in 17 green/white germplasms. Therefore, Csa3G904140 was taken as the likely candidate gene controlling the immature fruit color of cultivated cucumber. This study will contribute to the cloning of candidate genes and the development of white cucumber cultivars using marker-assisted breeding.
Highlights
Cucumber, Cucumis sativus L. (2n = 2x = 14), an important cucurbitaceous crop, is one of the top ten vegetables in the world
Gene mapping of pericarp color in wax gourd showed that the trait was controlled by one single gene; dark green color was dominant over yellow color, and the locus was located on chromosome 5 [3]
The fruit color of a tomato consisted of the pericarp color and flesh color, while the genetics between them were completely independent [5]; studies showed that the pericarp color was controlled by one pair of nuclear genes, where transparent color was recessive to yellow color [6]
Summary
The w0 white immature fruit skin color gene was located on Chr. at approximately 1150 kb in cucumber [12]. Wang et al [13] studied the genetics of the white immature fruit color trait in cucumber and identified the molecular marker SSR15312, which was located on Chr.. Genetic analysis of different F2 and backcross populations in cucumber revealed that one single dominant gene was associated with white immature fruit color in cucumber, and the locus was mapped to Chr.. Csa3G904140 was taken as one likely candidate gene These findings will facilitate marker-assisted selection of the white immature fruit color trait in cucumber breeding and the cloning of the white immature fruit color gene
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