Physiological and transcriptomic approaches reveal new insight into cadmium tolerance of Sesuvium portulacastrum L

Cadmium (Cd) pollution severely threatens to plant development and human health. As a phytoremediation species, S. portulacastrum possesses outstanding Cd accumulation ability. S. portulacastrum seedings was cultivated with half-strength Hoagland solution with 25 mg/L of CdCl₂, with Cd-free medium as control. After 14 days, treated plant kept growing but showed a 43.4% lower growth rate and 1.3 cm shorter roots. Leaf number increased and then decreased, whereas fresh weight increased continuously. The chlorophyll a/b ratio dropped to 1.89, suppressing photosynthesis. To eliminate excess ROS, plants activated comprehensive antioxidant systems: root SOD activity hit 192.64 U/g, root POD and stem CAT activities rose 2.8- and 4.6-fold separately. Cd accumulated predominantly in roots at 622.14 mg/kg, displaying obvious tissue specificity. Transcriptome analysis revealed 2461 and 4545 leaf DEGs, 2215 and 3004 root DEGs after 7 and 14 ds Cd exposure. Combined physiological and transcriptomic data uncovered two core Cd-tolerant mechanisms: metal transporters sequester toxic Cd²⁺ in vacuoles, and antioxidant systems scavenge ROS. Hub genes of key modules were enriched in glutathione metabolism, carbon metabolism, oxidative phosphorylation, peroxisome, protein processing, endocytosis and phenylpropanoid biosynthesis pathways. RT-qPCR validated the expression of representative metal transport and antioxidant hub genes, and heterologous GPX overexpression in yeast INVSc1 verified its function in boosting Cd tolerance. This study provides theoretical support for breeding heavy metal remediation plants via genetic engineering.