Functional interaction between Bacillus velezensis D103 and maize reveals a microbial mechanism for drought stress mitigation via photosynthesis and sugar metabolism

Drought stress severely limits maize productivity. Although plant growth-promoting rhizobacteria (PGPR) including Bacillus velezensis, are known to enhance drought tolerance, the underlying molecular mechanisms and essential host genes remain poorly defined. In this study, we demonstrate that B. velezensis D103 enhances maize drought tolerance through a coordinated physiological and molecular mechanism that preserves photosynthetic function and redirects carbon metabolism toward roots. Physiological analyses demonstrated that D103 inoculation improved photosynthetic performance and promoted root accumulation of carbohydrate under drought stress. Transcriptomic profiling revealed concurrent modulation of genes associated with photosynthesis and carbon metabolic pathways. Functional validation using virus-induced gene silencing (VIGS), we identified two distinct classes of host genes. Silencing of key non-compensable genes (ZmPsbXL, ZmSWEET13b, ZmPLT5, ZmGALX, and ZmFAB1D) eliminated the beneficial effects of D103, whereas drought tolerance was maintained in plants silenced for functionally compensable genes (ZmSWEET14, ZmRFS1, ZmBANGLUC) through activation of related paralogs, revealing a structured genetic network that confers functional resilience. Together, these findings establish a causal, gene-level framework for PGPR-mediated drought tolerance and highlight B. velezensis D103 as a promising microbial biostimulant for improving crop resilience to water limitation.