Amino Acid Transporter as a Potential Carrier Protein for the Root-to-Shoot Translocation of Polybrominated Diphenyl Ethers in Rice

This study finds that polybrominateddiphenyl ethers (PBDEs)were hitchhiked on the amino acid transporter to enable their root-to-shoottranslocation in rice plants. Astypical persistent organic pollutants, polybrominateddiphenylethers (PBDEs) tend to accumulate in edible parts of rice, posinggreat ecological and health risks. The translocation of PBDEs fromunderground to aboveground parts of rice is a crucial procedure todetermine the final bioaccumulation level. Herein, this study aimedto identify the transporter proteins for PBDEs in rice plants in orderto strengthen our understanding of the bioaccumulation mechanism andthe potential prevention strategy of the PBDE risk. Similar time-dependentpatterns were observed among the root-to-shoot translocation factors(TFs) of PBDEs, the expression of lysine histidine transporter (LHT)protein, and the relative levels of LHT substrates (phenylalanineor tyrosine), implying the potential co-transport of PBDEs, phenylalanine,and tyrosine by the carrier LHT. Fluorescence spectra and circulardichroism showed that PBDE congeners interfered with LHT via static fluorescence quenching and changes in the protein'ssecondary structure. The in vitro sorption fractionof LHT to PBDEs, as revealed by sorption equilibrium analysis, wascomparable to the in vivo TF values. Knockout of OsLHT1 in rice using CRISPR/Cas9 technology caused a 48.2-78.4%decrease in PBDE translocation. Molecular docking simulation suggestedthat PBDEs, phenylalanine, and tyrosine were inserted into the sameligand-binding cavity of LHT, substantiating the potential carrierrole of LHT for PBDEs from a conformational perspective. Quantitativestructure activity relationship analysis demonstrated that the ether-bondoxygen and the carbons at the site 4 and 4 & PRIME; of PBDE moleculesare significant determinants of the binding affinity with the LHTprotein and in vivo translocation of PBDEs. In summary,this study discovered that LHT acts as the cellular carrier for PBDEsand offered a comprehensive molecular explanation for the bioaccumulationand translocation of PBDEs in rice plants, covering both biologicaland chemical perspectives. These findings fill in a knowledge gapon the endogenous transporter proteins for exogenous organic pollutants.