High iron supply enhances cadmium accumulation in the aerial tissues by remodeling the root cell walls in Populus cathayana

Abstract

High iron (Fe) supply can enhance Cd accumulation in the aerial tissues of poplars, but the underlying mechanisms remain unknown. Here, we exposed Populus cathayana to either 0 or 120 µM CdCl₂ in combination with either 50 or 200 μM FeCl₃ for 30 days. We found that high Fe supply alleviated Cd-induced decreases in the concentrations of Fe and photosynthetic pigments in the leaves of P. cathayana, thereby improving the photosynthesis and total biomass. Additionally, high Fe increased the Cd^2 + influxes on the root tips and promoted Cd translocation from the roots to the aboveground tissues of P. cathayana. Consequently, the concentrations and total amount of Cd were increased in the aerial tissues of P. cathayana after adding high Fe. Interestingly, in the roots of Cd-treated P. cathayana, the expression levels of genes involved in cell wall remodeling were altered upon supplementation with high Fe, whereas the expression of transporter genes remained unchanged. High Fe addition resulted in the reconstruction of root cell walls of Cd-exposed P. cathayana, which reduced the Cd deposition in root cell walls, thereby promoting Cd translocation from the roots to the aerial tissues. A regulatory network dominated by several transcription factors and miRNAs, such as MYB103, WRKY33, miR397, and miR858, probably modulated the high Fe-caused root cell walls remodeling. These results suggest that high Fe enhances Cd accumulation in the aboveground tissues of P. cathayana by reconstructing the root cell walls, which is probably modulated by a regulatory network at both transcriptional and post-transcriptional levels.