Overexpression of PtrAREB3 improved cadmium enrichment and tolerance in poplar

Cadmium is a toxic heavy metal that has serious impacts on human and ecosystem health. Poplars play an active role in the phytoremediation of heavy metals in the environment; whereas only a few studies have investigated the molecular mechanisms by which trees absorb heavy metals from the environment. This study identified an abscisic acid-responsive element binding protein, PtrAREB3, in Populus trichocarpa. PtrAREB3 was principally expressed in leaves and markedly induced following the ABA and Cd treatments. Moreover, the poplar PtrAREB3 acts as direct regulator of target genes. Under Cd stress, PtrAREB3 further activates target genes associated with stress response and promotes cadmium tolerance of poplar by reducing the production of oxides, reducing chlorophyll degradation, increasing the synthesis of proline, and activating the antioxidant system. Furthermore, PtrAREB3 might indirectly regulate gene expression relating to Cd uptake, transport, and detoxification; ultimately, this increases Cd accumulation in plants. After 28 days of Cd treatment, the PtrAREB3 over-expression transgenic lines showed 18.2%- 25.7% higher dry biomass accumulation with a net photosynthesis rate than WT. In addition, overexpression of PtrAREB3 increased Cd accumulation in plants by 40.4%- 52.1%. Overall, the overexpression of PtrAREB3 enhanced Cd accumulation and tolerance, which making it an ideal molecular target for genetic improvement in Populus plants grown in metal contaminated areas in the future.