Plant-rhizosphere control of thallium mobility and detoxification in contaminated soils: Insights from multi-omics and in situ DGT.

Thallium (Tl) is an extremely toxic and strongly bioaccumulative metal increasingly detected in agricultural soils, yet its behavior at the plant-rhizosphere interface remains poorly constrained. Here, we integrated in situ diffusive gradients in thin films (DGT) with multi-omics analyses (transcriptomics, metabolomics, and 16S rRNA sequencing) to elucidate how plant-rhizosphere interactions regulate Tl mobility and detoxification in Brassica rapa. In situ DGT profiling coupled with the European Community Bureau of Reference (BCR) sequential extraction identified the root-soil interface (0-3 cm) as a hotspot of labile Tl dynamics, revealing a dose-dependent shift from rhizosphere-mediated Tl mobilization under moderate exposure to immobilization under high stress. This transition was mirrored by a hormesis-driven plant response, with low Tl levels stimulating growth and uptake (bioconcentration factor, BCF = 4.2), followed by growth inhibition and restricted translocation at higher doses. Multi-omics analyses showed coordinated metabolic and transcriptional reprogramming associated with this shift, including altered central carbon metabolism, glutathione homeostasis, phenylpropanoid biosynthesis, and selective regulation of metal transporters (ZIP downregulation; ABC and MATE upregulation). Key metabolites (L-proline, sinapoyl aldehyde) and genes (e.g., TAT, PRDX6) emerged as integrative regulators linking detoxification, redox balance, and osmoprotection. Concurrently, Tl exposure induced a functional succession of the rhizosphere microbiome toward metal-resistant taxa (e.g., Nitrospira, Microvirga), closely associated with changes in root exudation patterns. Collectively, these findings advance a process-based mechanistic understanding of how rhizosphere biogeochemistry, plant molecular responses and microbial dynamics jointly control Tl mobility and detoxification, informing Tl risk assessment and plant-microbe-assisted management.