Identification of a root-specific expression promoter in poplar and its application in genetic engineering for cadmium phytoremediation.

key messageA promoter, PRSEP7, was identified and confirmed to be specifically expressed in poplar roots. Poplar PRSEP7::CadWp transgenic lines showed high phytoremediation of Cd(II)-contaminated WPM and soil. Cadmium ions (Cd(II)) are heavy metals that are difficult for organisms to decompose in our natural environment. The generation of plants by genetic engineering with a high ability to phytoremediate Cd(II) from the soil is an ideal biological remediation strategy. Here, we identified and confirmed a promoter, PRSEP7, that is specifically expressed in poplar (Populus L.) roots. The promoter of PRSEP7 was then used to construct the poplar root expression vector 2301S-root. The CadW gene encoding a carbonic anhydrase (CA) was reported to play important roles in the phytoremediation of Cd(II) in microorganisms in a previous study. The sequence of CadW was optimized for plants, and the resulting gene CadWp also showed high activity for sequestration of Cd(II). CadWp was then introduced to 2301S-root to generate the PRSEP7::CadWp construct. This construct was used to transform poplar via Agrobacterium-mediated transformation. A number of stable transgenic poplar lines were generated, and two lines were randomly selected to test their ability to phytoremediate Cd(II). With several parameter measurements, the two transgenic lines showed high phytoremediation of Cd(II) under multiple growth conditions. Overall, we generated elite plant materials for the phytoremediation of Cd(II) in this study.