The antioxidative defense system is involved in the premature senescence in transgenic tobacco (Nicotiana tabacum NC89)

Background: alpha-Farnesene is a volatile sesquiterpene synthesized by the plant mevalonate (MVA) pathway through the action of alpha-farnesene synthase. The alpha-farnesene synthase 1 (MdAFS1) gene was isolated from apple peel (var. white winter pearmain), and transformed into tobacco (Nicotiana tabacum NC89). The transgenic plants had faster stem elongation during vegetative growth and earlier flowering than wild type (WT). Our studies focused on the transgenic tobacco phenotype. Results: The levels of chlorophyll and soluble protein decreased and a lower seed biomass and reduced net photosynthetic rate (Pn) in transgenic plants. Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide radicals (O-2(center dot-)) had higher levels in transgenics compared to controls. Transgenic plants also had enhanced sensitivity to oxidative stress. The transcriptome of 8-week-old plants was studied to detect molecular changes. Differentially expressed unigene analysis showed that ubiquitin-mediated proteolysis, cell growth, and death unigenes were upregulated. Unigenes related to photosynthesis, antioxidant activity, and nitrogen metabolism were downregulated. Combined with the expression analysis of senescence marker genes, these results indicate that senescence started in the leaves of the transgenic plants at the vegetative growth stage. Conclusions: The antioxidative defense system was compromised and the accumulation of reactive oxygen species (ROS) played an important role in the premature aging of transgenic plants.