Heterologous expression of EsSPDS1 in tobacco plants improves drought tolerance with efficient reactive oxygen species scavenging systems

• A novel spermidine synthase EsSPDS1 is isolated from Eutrema salsugineum.
• Overexpression of EsSPDS1 increases polyamines biosynthesis in transgenic tobacco plants.
• Overexpression of EsSPDS1 in transgenic plants enhances tolerance to drought stress with reduction of the ROS levels.

It has previously been indicated that polyamines (PAs) are involved in the response to adverse environmental stresses in various plant species. Increased cellular PA levels or exogenous PA application can reduce the accumulation of reactive oxygen species (ROS) imposed by multiple abiotic stresses via increasing antioxidant enzyme activities. In this study, a novel spermidine synthase gene, designated as EsSPDS1, was cloned and characterized from the halophytic plant Eutrema salsugineum. Analyses of tissue-specific expression profiles revealed that EsSPDS1 was expressed in almost all tested organs including leaves, stems, flowers, roots and siliques. The expression of EsSPDS1 was obviously induced by polyethylene glycol (PEG) and high salinity treatments. Furthermore, the EsSPDS1 transcripts rapidly accumulated upon exposure to abscisic acid (ABA) treatments, implying that this gene was involved in ABA-mediated abiotic stress response. Transgenic tobacco plants harboring EsSPDS1 exhibited enhanced drought tolerance relative to wild-type (WT) plants. These transgenic plants had lower levels of malondialdehyde (MDA), less ion leakage (IL) and reactive oxygen species (ROS). However, relative water content (RWC) and activities of antioxidant enzymes including SOD and CAT of the transgenic plants was remarkably higher than those of WT plants under drought stress conditions. Collectively, our data suggested that the activation of EsSPDS1 expression in tobacco plants conferred drought tolerance, which might be attributed to enhance the ability to scavenge ROS levels.