Integration of Cytological and Transcriptomics Analyses Reveals How Escherichia coli Inoculation Enhances Suaeda Salsa Root Growth and Alleviates Cadmium‐Salt Stress

To explore how plant growth-promoting rhizobacteria (PGPR) regulate stress-tolerant plant growth and enhance heavy metal remediation under combined cadmium (Cd) and salt stress, we conducted hydroponic experiments using Suaeda salsa inoculated with Escherichia coli-10,527. We investigated the changes in plant growth and stress tolerance, Cd translocation, cell ultrastructure, Cd subcellular distribution, and gene expression under hydroponic conditions. The results showed that inoculation improved plant biomass, stress tolerance, and Cd uptake, particularly under low Cd/salt concentrations. E. coli-10,527 colonized lateral root zones and secreted extracellular polymeric substances (EPS), which promoted flavonoid accumulation (by 12.68%-36.76%), thereby enhancing root growth and Cd accumulation. Compared with the uninoculated control, E. coli-10,527 inoculation altered the subcellular distribution of Cd in S. salsa; the proportion of Cd in the cytoplasm increased from 16.29% (29.06%) to 24.28% (45.57%) in roots (shoots). Transcriptomic analysis revealed the upregulation of genes (ZIPA, NRAMP3, and HMA4) potentially involved in enhanced Cd transport and vacuolar sequestration. Overall, inoculation with E. coli-10,527 can promote root development in S. salsa under Cd and salt stress, while facilitating simultaneous phytoremediation of Cd and salt. This study provides an effective microbial inoculation strategy for Cd remediation in saline soils affected by combined stresses.