Haplotype networking of GWAS hits for citrulline content indicates positive selection leading to the domestication of watermelon

Authors: VIJAY, JOSHI - Texas A&M University; SUHAS, SHINDE - West Virginia State University; VENKATA LAKSHMI, ABBURI - West Virginia State University; LOPEZ, CARLOS - West Virginia State University; PADMA, NIMMAKAYALA - West Virginia State University; Levi, Amnon; UMESH, REDDY - West Virginia State University

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2019
Publication Date: 10/29/2019
Citation: Vijay, J., Suhas, S., Venkata Lakshmi, A., Lopez, C., Padma, N., Levi, A., Umesh, R. 2019. Haplotype networking of GWAS hits for citrulline content indicates positive selection leading to the domestication of watermelon. International Journal of Molecular Sciences [MDPI]. https://doi.org/10.3390/ijms20215392.
DOI: https://doi.org/10.3390/ijms20215392

Interpretive Summary: Citrulline is an amino acid produced in watermelon fruits and is considered to have health promoting benefits like reducing the risk of cardiovascular diseases. There is an interest by consumers to increase the nutritional value of sweet dessert watermelons by enriching their citrulline content. However, little is known about the genetic mode of citrulline production in watermelon. A scientist at the USDA, ARS, U.S. Vegetable Laboratory in Charleston, SC, has initiated collaboration with scientists at West Virginia State University and with a scientist at Texas A&M University on evaluating citrulline concentration in watermelon accessions collected in the wild in Africa and in sweet dessert watermelon varieties. The scientists used advanced genomic technology tools to identify the gene loci involved in production of citrulline in watermelon. The gene loci identified in this study could be useful for University researchers and seed company breeders working to increase the nutritional value of watermelon.

Technical Abstract: Watermelon (Citrullus lanatus) is a viable source of nutrients. Among them is the non-protein amino acid citrulline which is involved in production of nitric oxide via arginine, and plays a role in nitrogen transport and maintenance of cellular osmolarity during plant abiotic stresses. The objective here was to use genome-wide association study (GWAS) to identify single nucleotide polymorphism (SNP) markers associated with citrulline metabolism. Genome sequence analysis was conducted for 187 watermelon accessions. Population structure division and phylogenetic analyses were conducted using a total of 12,125 SNPs with minor allele frequency (MAF)'>'0.05. The watermelon cultivars analyzed in this study had an increased citrulline content compared with landraces and egusi type watermelons, indicating that higher citrulline content could be associated with domestication of the sweet dessert watermelon. Candidate genes, including Ferrochelatase and Acetolactate synthase with SNPs significantly associated with citrulline content were identified and their expression was validated using a real time PCR analysis. The quantitative trait loci (QTL) and candidate genes identified in this study can be useful for development of markers used in breeding programs aimed to enhance citrulline production in elite watermelon varieties.