Sequencing and resequencing of watermelon genomes

Watermelon, Citrullus lanatus var. lanatus, is an important cucurbit crop that contributes to food and economic security in addition to human nutrition. We have generated and assembled a high-quality draft genome sequence of watermelon, which covered 83% of the estimated 425 Mb watermelon genome. Over 93% of the assembled genome was anchored to 11 watermelon chromosomes. Approximately 45% of the genome sequence corresponded to repeats, consisting mainly of long terminal repeats. Gene prediction identified 23,440 protein coding genes. We will present an evolutionary scenario for the origin of the eleven watermelon chromosomes, derived from a seven-chromosome paleohexaploid eudicot ancestor. Initial analysis of resequencing data of 21 watermelon genomes, including those of East-Asia and America ecotypes and wild accessions of Citrullus lanatus subsp. lanatus, Citrullus lanatus subsp. Citroides, and Citrullus colocynthis, will be presented. Our extensive genomic analyses coupled with transcriptomic analyses identified genes critical to valuable fruit quality traits, including rapid fruit expansion, sugar accumulation, and metabolism of important nutritional metabolites including lycopene and citrulline.