Agrobacterium-mediated transformation system for the drought and excess light stress-tolerant wild watermelon (Citrullus lanatus)

Abstract

Wild watermelon plants are drought and excess light stress-tolerant despite carrying out normal C₃-type photosynthesis. In this study, a system was established for the genetic transformation of wild watermelons. Adventitious shoots were induced efficiently from cotyledon explants on medium containing 4 mg l⁻¹ of benzyladenine. The explants were infected with Agrobacterium carrying a plasmid containing selectable marker genes, nptII (neomycin phosphotransferase), hpt (hygromycin phosphotransferase), and a reporter gene gusA (β-glucuronidase). A β-Glucuronidase (GUS) histochemical assay showed that kanamycin was more effective than hygromycin as the selective agent for transformation. The presence of T-DNA in the regenerated shoots was confirmed by amplification of the transgene using polymerase chain reaction. Southern blot analysis revealed stable integration of the transgene in the T₁ progeny. The system presented here will provide an experimental basis for molecular studies of wild watermelon genes, and thus facilitate an understanding of their contribution to stress tolerance in this plant.