Microbial biofilms as drought shields: Bacillus velezensis D103 enhances maize tolerance via aquaporin regulation

Drought stress severely constrains crop productivity, and while plant growth-promoting rhizobacteria (PGPR) are known to enhance drought tolerance by modulating host aquaporins (AQPs), the specific role of bacterial biofilm formation in this regulatory process remains poorly understood. Here, we demonstrate that biofilm formation is a pivotal mechanism through which Bacillus velezensis D103 confers drought resilience to maize. Under drought stress, maize root exudates synergistically enhanced D103 biofilm formation, which was essential for robust root colonization and mediated a drought-adaptive restructuring of the rhizosphere microbiome. Crucially, we found that an intact bacterial biofilm systemically upregulated key plant AQPs (ZmPIP2;6 and ZmTIP1;1), thereby enhancing root water transport capacity. Using virus-induced gene silencing, we further clarified the molecular mechanism underlying this biofilm-aquaporin link, revealing that ZmPIP2;6 is indispensable for D103-conferred drought tolerance. Our findings refine the current understanding of PGPR-mediated drought tolerance, highlighting that biofilms coordinate host AQP expression, rhizosphere microbiome assembly, and soil water retention to enhance drought resilience. This work provides a mechanistic basis for developing effective microbial inoculants.