Melatonin strongly enhances the Agrobacterium- mediated transformation of carnation in nitrogen-depleted inoculation and co-cultivation media

With the rising demand for new cultivars of carnation, efficient transformation protocols are needed to enable the bioengineering of new traits. Here, we established a novel and efficient Agrobacterium -mediated transformation system using callus as the target explant for four commercial carnation cultivars. Leaf-derived calli of all cultivars were inoculated with Agrobacterium tumefaciens strain LBA4404 containing the plasmid pCAMBIA 2301 harboring genes for β-glucuronidase ( uidA ) and neomycin phosphotransferase ( npt II). Polymerase chain reaction (PCR) and histochemical assays confirmed the presence of uidA and β-glucuronidase (GUS), respectively in transgenic shoots. The effect on transformation efficiency of medium composition and the presence of antioxidants during inoculation and co-cultivation was investigated. The transformation efficiency was increased to 5% in Murashige and Skoog (MS) medium lacking KNO 3 and NH 4 NO 3, compared to 0.6% efficiency in full-strength medium. The omission of other components including the entire macro- and microelements, Fe or vitamins from MS medium was also observed to increase gene transfer. Transformation efficiency was increased dramatically to 24.4% across all carnation cultivars by the addition of 2 mg/l melatonin to nitrogen-depleted MS medium. Shoot regeneration was also doubled in this treatment. The establishment of this efficient and reliable transformation protocol can advance the development of novel carnation cultivars through molecular breeding approaches.