Functional Analysis of Key Transporter Genes Involved in Cadmium Uptake and Translocation in Wheat

While the molecular mechanisms of cadmium (Cd) uptake are well-studied in rice and tobacco, hexaploid wheat remains less explored. Elucidating the roles of transporter genes in Cd uptake and translocation in wheat is critical for minimizing Cd accumulation in grains. This study compared the differences in the expression levels of Cd transporter families (including the natural resistance-associated macrophage protein (NRAMP), heavy metal ATPase (HMA), zinc-regulated transporter/iron-regulated transporter (ZIP), and yellow stripe-like (YSL) families) between two high Cd-accumulating wheat varieties and two low Cd-accumulating wheat varieties using qPCR. We found that low Cd-accumulating wheat varieties had higher expression levels of TaNRAMP5 and TaHMA2 in roots and TaHMA3 in aboveground tissues, and lower expression levels of TaNRAMP6, TaZIP5, and TaYSL6 in both roots and aboveground tissues compared to the high Cd-accumulating wheat varieties. Mantel test analysis revealed that the root expression levels of TaNRAMP5 and TaNRAMP6 and aboveground expression levels of TaZIP6 and TaHMA2 were significantly correlated with the Cd content of wheat tissues. Furthermore, the expression levels of TaZIP5 in roots and TaZIP5 and TaHMA3 in aboveground tissues were significantly correlated with the Cd translocation factor from roots to aboveground tissues, suggesting that TaNRAMP5, TaNRAMP6, TaZIP6, and TaHMA2 played key roles in Cd uptake and accumulation in wheat, and TaZIP5 and TaHMA3 were closely associated with Cd translocation from roots to aboveground tissues. Compared to low Cd-accumulating varieties, high Cd-accumulating wheat varieties exhibit significantly elevated levels of thiol-containing compounds for Cd chelation, including glutathione (7.65%~75.5% higher), phytochelatins (2.35%~47.2% higher), and non-protein thiols (13.2%~37.1% higher). These findings deepen insights into wheat Cd absorption processes. The identified transporter genes could serve as foundational resources for future breeding strategies aimed at reducing Cd accumulation in wheat, pending further functional validation.