Downregulation of the lycopene ε-cyclase gene confers tolerance to salt and drought stress in Nicotiana tabacum

Lycopene epsilon-cyclase (epsilon-LCY) functions at a branch point of the carotenoid biosynthesis pathway and modulates the ratio of lutein to the beta-carotenoids. RNA interference (RNAi) and overexpression (OE) of Nt epsilon-LCY were used to evaluate the physiological roles of epsilon-LCY in Nicotiana tobacum. In leaves, strong accumulation of beta-branch carotenoids and high expression of carotenoid biosynthesis genes resulted from suppression of Nt epsilon-LCY expression. RNAi plants showed enhanced salt and drought tolerance, while overexpression of the Nt epsilon-LCY gene weakened tolerance to salt and drought stress, as compared to control. Further analysis revealed that RNAi plants exhibited less water loss and had lower reactive oxygen species levels than did WT plants after both the salt and drought treatments. Further, higher levels of ABA accumulated in the RNAi lines than in the WT lines under stress conditions. These results suggest that reduced Nt epsilon-LCY expression can improve drought and salinity tolerance in Nicotiana tabacum by enhancing their ROS scavenging ability.