Microbe-mediated regulation of cadmium partitioning and intra-plant detoxification in the medicinal plant Solanum aculeatissimum

Abstract

Soil cadmium (Cd) pollution poses a serious threat to agricultural ecosystems, and plant-microbe interactions offer a promising strategy for Cd remediation. Solanum aculeatissimum is a medicinal and industrial plant with high Cd tolerance and accumulation potential, yet its interactions with associated microorganisms under Cd stress remain unclear. Metagenomic analyses revealed that Cd stress significantly reduced rhizosphere microbial diversity and promoted the enrichment of Cd-tolerant and potentially beneficial microorganisms. Notably, the abundance of Achromobacter increased markedly under high Cd treatment. Two core Achromobacter strains, Hach1 and Hach3, were isolated from roots. Both strains exhibited multiple plant growth-promoting traits, tolerated 800 mg/L Cd²⁺, and achieved Cd removal rates exceeding 60% in liquid culture. Inoculation experiments demonstrated that Hach1 significantly increased root Cd content by 35.6% and alleviated Cd-induced oxidative damage primarily by enhancing POD and CAT activities. In contrast, Hach3 enhanced Cd translocation to stems by 61.4% and to leaves by 56.2%, while improving Cd tolerance through enhanced SOD activity and proline accumulation. At the transcriptional level, application of the two core strains differentially regulated the expression of heavy metal ATPase (HMA) gene family members, thereby influencing Cd spatial distribution within plants. This study systematically elucidates the mechanisms underlying the cooperative responses of S. aculeatissimum and Achromobacter to Cd stress, providing mechanistic insights into plant-microbe interactions associated with Cd tolerance and adaptation.