The Heavy Metal-Associated Isoprenylated Plant Protein (HIPP) Gene Family Plays a Crucial Role in Cadmium Resistance in Lotus (Nelumbo nucifera G.)

Cadmium (Cd) contamination poses significant threats to aquatic ecosystems. Heavy metal-associated isoprenylated plant proteins (HIPPs) are plant-specific chaperones involved in metal ion homeostasis and stress adaptation. Lotus is an aquatic plant with high biomass and Cd accumulation capacity, showing great potential in water remediation. However, the functional characterization of HIPPs in lotus remains unexplored, limiting its application in phytoremediation. We conducted comprehensive characterization of NnHIPP genes in lotus, integrating comparative genomics, Cd-stress transcriptomics, and heterologous expression assays in transgenic yeast. This study identified 33 NnHIPP genes classified into five subfamilies with conserved motifs and structures. Synteny analysis revealed closer evolutionary relationships with dicots (Arabidopsis and Medicago sativa) than monocots. Abundant stress-responsive elements were found in NnHIPPs promoters. Tissue-specific expression profilings indicated functional diversification across organs and developmental stages. Our transcriptome analysis revealed that most NnHIPPs responded to Cd stress, with stronger induction in roots than leaves. Four Cd-induced NnHIPPs (NnHIPP10/14/21/33) showed both plasma membrane and nuclear localization. Notably, NnHIPP14, NnHIPP21, and NnHIPP33 conferred varying degrees of Cd tolerance when overexpressed in yeast. Our study demonstrates that NnHIPPs participate in Cd stress response. Three candidate NnHIPP genes are proposed for genetic engineering to enhance phytoremediation efficiency in lotus.