Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/25/2006
Publication Date: 6/15/2006
Citation: Joobeur, T., Gusmini, G., Zhang, X., Levi, A., Yong, X., Wehner, T., Oliver, M., Dean, R. 2006. Construction of a watermelon BAC library and identification of SSRs anchored to melon or Arabidopsis genomes. Theoretical and Applied Genetics. 112:1553-62. Interpretive Summary: Watermelon is a major vegetable crop in the U.S. and in recent years there has been an increased demand by consumers for high- quality seedless watermelons. Over 60% of the watermelons produced in the U.S. in 2004 were seedless. The watermelon industry has great interest in enhancing the nutritional value of seedless watermelons, particularly in enhancing the naturally occurred carotenoid pigment called lycopen in watermelon. Lycopen is known to be a main dietary source of vitamin A in humans, and is associated with reduced risk of cancer, heart disease and eye degeneration. Developing watermelon cultivars with increased lycopen concentrations will benefit consumer health. However, there is insufficient information about the genes controlling lycopen production in watermelon. In this study, an ARS scientist collaborated with researchers at North Carolina State University on developing a DNA library containing the genes that control watermelon fruit development and quality. The results in this study will be useful for gene discovery and for further improvement of cultivars with increased watermelon fruit quality and nutritional values.
Technical Abstract: A bacterial artificial chromosome (BAC) library was constructed for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] with an average insert-size of 106 kb, providing 21 haploid genome equivalents. The library was used to identify BAC clones that are anchored to probes evenly distributed on the genomes of melon or Arabidopsis. Twenty-eight probes (representing 66% of the tested probes) from melon and 30 probes (65%) from Arabidopsis identified positive BAC clones. Two methods were implemented to identify SSRs from the positively hybridizing BAC clones. First, analysis of BAC end sequences revealed 37 SSRs. For the second method, pooled DNA of BACs identified by the melon probes was used to develop a shotgun library. The library was then screened with synthetic SSR oligonucleotides by hybridization. Sequence analysis of positively hybridizing shotgun clones revealed 142 different SSRs. Thirty-eight SSRs were characterized using 3 watermelon cultivars, 5 plant introduction (PI) accessions of C. lanatus var lanatus and 4 PIs of C. lanatus var citroides. Of these, 36 (95%) were found to be polymorphic with up to 6 alleles per marker. Polymorphism information content values for polymorphic markers varied between 0.22 and 0.79 with an average of 0.53. The methods described herein will be valuable for the construction of a watermelon linkage map with SSRs evenly distributed on its genome that is anchored to the genomes of melon and Arabidopsis.