<i>Bacillus siamensis</i> orchestrates plant gene reprogramming and rhizosphere microbiome reshaping to bolster maize crop performance

Abstract Plant growth‐promoting rhizobacteria (e.g., Bacillus ) confer health benefits to the host. Bacillus siamensis has been used to control plant disease in fruits and vegetables, but its potential effects on crop performance remain unclear. This study investigated changes in the growth, root transcriptomic profile, and rhizosp here microbiome of maize plants ( Zea may L.) following inoculation with B. siamensis 33. All inoculated plants grew better than non‐inoculated controls in pots, as exemplified by 24.0% and 6.8% increase in plant height and stem diameter, respectively ( p &lt; 0.01). Shoot dry weight also increased by 20.6% upon inoculation, accompanied by 46.9% increase in root dry weight ( p &lt; 0.01). Transcriptomic analysis revealed that inoculation induced (2.16‐ to 5.53‐fold) upregulated expression of genes related to auxin signal transduction in maize. The expression of genes involved in phenylpropanoid biosynthesis, glutathione metabolism, and plant defense‐related signal (e.g., jasmonic acid and salicylic acid) transduction was (2.06‐ to 11.30‐fold) upregulated in inoculated plants. Upon inoculation, bacterial α‐diversity trended higher and potentially beneficial taxa (e.g., Sphingobium , Flavihumibacter , and Parasegetibacter ) were enriched in the rhizosphere, likely a result of enhanced root exudation of specific metabolites (e.g., flavonoids) and subsequent recruitment of beneficial microbial taxa. Potential microbial functions associated with nitrogen cycling and pollutant degradation were stimulated by inoculation. These findings indicate that B. siamensis 33 mediates the reprogramming of plant gene expression and reshaping of rhizosphere microbiome structure to bolster maize crop performance.