Production of transgenic Nicotiana sylvestris plants expressing melatonin synthetase genes and their effect on UV-B-induced DNA damage

We have obtained transgenic plants of Nicotiana sylvestris expressing an arylalkylamine N-acetyltransferase (AANAT) gene and a hydroxyindole-O-methyltransferase (HIOMT) gene using Agrobacterium tumefaciens-mediated transformation. Both AANAT and HIOMT are key enzymes in melatonin synthesis. Transgenic plants of N. sylvestris were characterized by polymerase chain reaction (PCR) and reverse transcription PCR analyses. The content of melatonin was significantly higher in transgenic plants than in nontransgenic plants. The highest melatonin content of transgenic plant leaves reached 50.4 mu g/g dry weight, while almost no melatonin could be detected in the nontransformed plants. To investigate effects of the expression of the AANAT and HIOMT genes on melatonin function in plants, isolated protoplasts of N. sylvestris were exposed to ultraviolet (UV)-B radiation for different durations. DNA damage was evaluated by single-cell gel electrophoresis, which showed that the TailDNA percentage value in transgenic protoplasts was lower than that in the nontransformed protoplasts in the range of 0-30 s of UV-B radiation. DNA damage caused by UV-B was therefore reduced in transgenic N. sylvestris plants.