| dc.description.abstract | Citrulline is a non-protein amino acid synthesized from ornithine and carbamoyl phosphate in plants. Experiments were performed to understand, (1) the partitioning of citrulline in watermelon plants during the development, (2) impact of environmental stresses (drought, heat, salt and nitrogen) on citrulline metabolism, (3) transcriptomic changes in the citrulline metabolism in response to drought and salt stress, and (4) the variability in seed-specific amino acids and proteins in watermelon germplasm. Based on the dynamic amino acid profiling of the watermelon plant during the development, fruit flesh and rind accumulated the highest amounts of citrulline. The moderate amount of citrulline in leaf and stem tissues suggested the possibility of translocation of citrulline from the vegetative (source) to fruit (sink) tissues. Citrulline accumulation was positively correlated with ornithine (precursor) and arginine (catabolic product). Rapid induction (38-fold in drought and 9.4-fold in salt stress) of citrulline in the vegetative tissues suggests its utility as a potential biomarker during drought and salt-stress induced responses. Heat stress significantly suppressed the synthesis of citrulline metabolism but activated the accumulation of N-rich amino acids (glutamine and asparagine), indicating the existence of citrulline-independent novel mechanisms of heat tolerance in watermelon.
Our data demonstrated that citrulline biosynthesis was regulated by nitrogen status and plays a role in translocating nitrogen based on the reduction of citrulline content in various tissues and down-regulation of genes, AAT and CPS2 (citrulline biosynthesis genes) during nitrogen limitations in watermelon
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RNA-Seq analysis of drought and salt-induced watermelon plants identified over 3900 and 7600 differentially expressed genes, respectively. Consistent with our real-time quantitative PCR studies, RNA-Seq analysis confirmed the up-regulation of biosynthetic genes (AAT, AOD, OTC, and CPS2) and down-regulation of catabolic genes (ASS, ASL, ODC, OCD) further supporting the increased accumulation of citrulline during drought stress.
A detailed survey showing significant variation in the content of various amino acids and total crude proteins across the watermelon germplasm opened up opportunities for genetic mapping and marker-assisted selection to enhance these traits in the cultivated varieties. | en |
