Genome-wide identification of HIPP genes family in sorghum reveals the novel role of SbHIPP40 in accumulation of cadmium.

Excessive Cadmium (Cd) content in soil poses a significant threat to plant growth and human health. Heavy metal-associated isoprenylated plant proteins (HIPPs) are pivotal regulators of metal homeostasis and detoxification. While Sorghum (Sorghum bicolor) is a promising phytoremediation crops, the functional roles of its HIPPs family remain poorly characterized. Here, we identified 45 SbHIPP genes in sorghum through genome-wide analysis. Among these, SbHIPP40 exhibited predominantly expression in leaves and roots, with marked upregulated under Cd exposure. Subcellular localization assays revealed nuclear and plasma membrane targeting of SbHIPP40. Functional validation in yeast demonstrated SbHIPP40 overexpression enhanced Cd tolerance in the ycf1 mutant strain. Transgenic rice SbHIPP40 overexpressing accumulated 1.68-3.92 fold higher Cd in stems, leaves, and grains compared to wild-type plants. Transcriptomic profiling revealed that SbHIPP40 modulates key pathway in signal transduction and stress responses. Mutagenesis studies highlighted the indispensable role of the HMA domain in Cd binding, as its deleting drastically reduced Cd accumulation and impaired yeast growth, whereas truncation of other domain, such as isoprenylation motif, had no significant effect. Our findings establish SbHIPP40 as a pivotal Cd accumulator via its HMA domain, advancing understanding of sorghum's Cd detoxification mechanisms and offering a genetic resource for enhancing phytoremediation strategies.