Multiomics reveals an essential role of long-distance cadmium translocation in regulating plant cadmium resistance and grain cadmium accumulation in allohexaploid wheat (Triticum aestivum L.) genotypes

Abstract Cadmium (Cd) easily enters cereal roots and is translocated to the shoots and grains thus posing risks to human health. Vastness and complexity of the allothexaploid wheat genome is a huge challenge for understanding its Cd resistance and accumulation. Herein, wheat plants of a Cd-resistant genotype (‘ZM1860’) and a Cd-sensitive genotype (‘ZM32’), selected from 442 wheat cultivars, exhibited significantly differential plant Cd resistance. Integrated comparative analyses of morpho-physiological investigation, ionomic and phytohormone profiling, genomic variations, transcriptomic landscapes, and functional analysis was performed to identify the mechanisms underlying differential Cd resistance. Under Cd toxicity, ‘ZM1860’ outperformed than ‘ZM32’ with obvious leaf chlorosis, weaker root architecture, ROS over-accumulation, and disordered phytohormone homeostasis. Ionomics showed that ‘ZM32’ had a higher translocation coefficient of Cd from roots to shoots and accumulated more Cd in grains than ‘ZM1860’. Whole-genome re-sequencing (WGS) and transcriptome sequencing identified numerous DNA variants and differentially expressed genes involved in abiotic stress responses and ion transport. Integrated ionomics, transcriptomics, and functional analyses identified the plasma membrane-localized TaHMA2b-7A as a central Cd exporter regulating differential long-distance Cd translocation in wheat genotypes. WGS- and PCR-based sequence polymorphisms revealed a 25-bp InDel site in the promoter region that might determine the differential gene expression of TaHMA2b-7A with same amino acid sequences in wheat gonotypes. The multi-omics approach used here eased the identification of wheat core transporters involving long-distance Cd translocation, and may provide elite gene resources for the genetic improvement of plant Cd resistance and grain Cd accumulation in wheat and other cereal species.