Fungal-derived nanoparticles confer cadmium tolerance in maize through transcriptional reconfiguration and microbiome...

The application of nanotechnology presents a promising strategy for mitigating heavy metal toxicity in crops, yet the integrative mechanisms underlying nanoparticle-mediated stress alleviation across the plant-soil system remain poorly understood. Herein, we investigated the transcriptomic and rhizosphere microbial responses of maize to cadmium (Cd) stress and the responses associated with fungal-mediated iron-based nanoparticles (NPs). Characterization confirmed the synthesis of spherical, Fe-O dominant NPs with uniform distribution. Under Cd stress, transmission electron microscopy revealed severe ultrastructural damage in leaf cells, which was associated with pronounced cellular alterations, whereas NPs application was associated with preservation of leaf ultrastructure. RNA-sequencing analysis demonstrated that Cd stress triggered extensive transcriptional reprogramming, suppressing defense-related and phenylpropanoid biosynthetic genes while activating stress-signaling pathways. NPs treatment alone was associated with a distinct transcriptional response, including changes in defense and metabolism-related genes without pronounced stress-associated transcriptional signatures. In NPCd co-treated plants, NPs were associated with reversal of Cd-induced transcriptional changes, particularly in starch/sucrose and phenylpropanoid metabolism and ethylene and jasmonate related signaling pathways. Rhizosphere microbiome analysis further revealed that NPs application significantly altered bacterial diversity and community composition, with treatment-associated shifts in several bacterial genera, including Sphingomonas and Methylobacterium. Collectively, the results showed that fungal-mediated NPs application was associated with improved Cd tolerance in maize, accompanied by preservation of leaf ultrastructure, reduced Cd-associated superoxide accumulation, transcriptional reprogramming of defense and metabolism related pathways, and changes in rhizosphere bacterial communities. These findings highlight the potential of fungal-mediated NPs as a promising strategy for improving crop performance under Cd stress.