Abstract
Dwarf habit is one of the most important traits in crop plant architecture, as it can increase plant density and improved land utilization, especially for protected cultivation, as well as increasing lodging resistance and economic yield. At least four dwarf genes have been identified in watermelon, but none of them has been cloned. In the current study, the Cldw-1 gene was primary-mapped onto watermelon chromosome 9 by next-generation sequencing-aided bulked-segregant analysis (BSA-seq) of F2 plants derived from a cross between a normal-height line, WT4, and a dwarf line, WM102, in watermelon. The candidate region identified by BSA-seq was subsequently validated and confirmed by linkage analysis using 30 simple sequence repeat (SSR) markers in an F2 population of 124 plants. The Cldw-1 gene was further fine-mapped by chromosome walking in a large F2 population of 1,053 plants and was delimited into a candidate region of 107.00 kb. Six genes were predicted to be in the candidate region, and only one gene, Cla010337, was identified to have two single nucleotide polymorphisms (SNPs) and a single nucleotide deletion in the exons in the dwarf line, WM102. A derived cleaved amplified polymorphic sequence (dCAPS) marker was developed from the single nucleotide deletion, co-segregated with the dwarf trait in both the F2 population and a germplasm collection of 165 accessions. Cla010337 encoded an ATP-binding cassette transporter (ABC transporter) protein, and the expression levels of Cla010337 were significantly reduced in all the tissues tested in the dwarf line, WM102. The results of this study will be useful in achieving a better understanding of the molecular mechanism of the dwarf plant trait in watermelon and for the development of marker-assisted selection (MAS) for new dwarf cultivars.
Highlights
Cultivated watermelon (Citrullus lanatus var. lanatus (Thunb.) Matsum. & Nakai) is an important horticultural crop in the Cucurbitaceae family and is one of the most widely consumed fresh fruits worldwide
Though the plant height and internode length were varied at different developmental stages in various environments, the relative length of plant height and internode length were significantly reduced in the dwarf inbred line, WM102, being almost half that in the normal-height line, WT4 (Table 1, Figure 1 and Figure S1)
The results showed that only the dCAPS3 marker was completely consistent with the phenotyping (Figure S4A), while the Indel1 marker developed from the 8th intron was not in complete agreement with the phenotype (Figure S4B), suggesting that the 5-bp deletion in the intron of Cla010337 was not conserved among different watermelon accessions
Summary
Cultivated watermelon (Citrullus lanatus var. lanatus (Thunb.) Matsum. & Nakai) is an important horticultural crop in the Cucurbitaceae family and is one of the most widely consumed fresh fruits worldwide. Fine Mapping of a Dwarf Gene (Indel) markers have been developed from the assembly of the watermelon genome (Ren et al, 2012; Zhu et al, 2016). The rapid development of genetic and genomic resources in watermelon was greatly facilitated by gene and QTL mapping. A number of genes controlling important traits in watermelon have been mapped and cloned, such as fruit shape (Dou et al, 2018), flesh color (Zhang et al, 2017), the tonoplast sugar transporter gene (ClTST2) (Ren et al, 2018), and lobed leaf shape (Wei et al, 2017), as well as QTLs associated with resistance to different pathogens (Lambel et al, 2014; Kim et al, 2015; Ren et al, 2015; Branham et al, 2017)
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