Hydroponic experiments and computational simulations were conducted to investigate the changes in the gene expression, structure, and binding mode of the rice transporter protein OsTIL to OPEs by the presence of Cd 2+ and Zn 2+ . OPEs and Zn 2+ were observed to promote seedling growth and OPEs alleviated the suppressive effect of Cd 2+ on seedlings. Usually, Cd 2+ and Zn 2+ inhibited the accumulations of OPEs in plants accompanied by the decrease of RCF (root concentration factor) and TF (transport coefficient). In particular, Zn 2+ promoted TDCPP accumulation only in roots accompanied by the increase of RCF and the decrease of TF. Furthermore, Cd 2+ and Zn 2+ affected the gene expressions of OPEs transporter-OsTIL response in the accumulation of OPEs in both single and compound pollution. After molecular dynamics simulation analysis, RMSD of the protein backbone, binding pocket, and ligand only in TDCPP-OsTIL complex also were significantly affected by two metal ions. Furthermore, two metal ions can press the interaction of OPEs and OsTIL by reducing the stability of protein structure and the numbers of HB (hydrogen bonds) and enlarging the pocket. However, Zn 2+ extra supports an enlarged entrance for TDCPP, which could facilitate the entry of the coordination complex of Zn 2+ with TDCPP into the pocket and improve TDCPP capacity of OsTIL.
To understand uptake and accumulation process of organophosphate esters (OPEs), growth, concentrations of OPEs, and transcript regulation of lipid transporters in rice seedlings were investigated under six OPE congeners exposures. The increase of seedlings’ growth and accumulation of OPEs in plants were observed. Root concentration factors (RCFs) of aryl-OPEs were the highest in consistent with their strong hydrophobicity, indicating that they were more liable to be accumulated in roots. Meanwhile, shoot/root concentration factors (SRCFs) of halogenated alkyl-OPEs were the highest in accordance with their low hydrophobicity, implying that they were easily translocated to shoots. Lipid transporters involved in uptake and accumulation of OPEs, evidence from the transcript responses of their lipid transporters. Moreover, the only positive relationship between OsTIL expressions and accumulation of OPEs demonstrated the dominant role of OsTIL among the investigated transporters. In addition, although all of OPE congeners could be docked into active cavities of OsTIL with varied markedly binding affinities, hydrophobicity OPEs performed stronger binding energy with OsTIL after homology modeling and molecular docking analysis. Therefore, uptake and accumulation of OPEs were corporately charged by OPEs’ physicochemical properties and lipid carrier transports in coincidence with the experimental observation about accumulation of OPEs in roots and shoots.
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