Bacillus cereus T146 Enhances Wheat Salt Tolerance by Restructuring the Rhizosphere Microbiome and Activating TaPIN1-Dependent Auxin Transport.

Salinity stress disrupts rhizosphere homoeostasis and inhibits root development. Although PGPR are known to alleviate such stress, critical knowledge gaps remain regarding the specific mechanisms by which they enhance tolerance under moderate to high salinity, particularly within the wheat rhizosphere -root interface. Here, we show that Bacillus cereus T146, isolated from saline-alkali soil, enhances wheat salt tolerance through two integrated mechanisms. Metagenomic and culturomic analyses further revealed that T146 enriches IAA-producing Pseudomonas in the rhizosphere, and co-inoculation experiments demonstrated that these recruited bacteria contribute synergistically to salt tolerance. On the host side, transcriptomic and cell biological analyses demonstrated that T146 reactivates salt-suppressed auxin pathways. Specifically, inoculation upregulates key regulators of lateral root development (PLT3, PLT7, GLV6) and increases PIN1, PIN2, and PIN3 abundance, leading to elevated auxin accumulation as indicated by DR5::GFP signals. Importantly, silencing TaPIN1 largely compromised T146-induced tolerance and transcriptional reprogramming, demonstrating a functional interplay between microbiome modulation and host hormonal regulation. These results reveal that T146 synergistically promotes salinity resilience by coordinating rhizosphere microbiome remodelling with auxin-mediated root development, offering a mechanistic framework for microbiome-based strategies to improve crop stress tolerance.