Abstract
<title>Abstract</title> <p> Plant-associated bacteria can influence plant growth, development, and stress responses, yet the mechanisms underlying stable interactions with host plants remain incompletely understood. Here, we characterized <italic>Paenibacillus</italic> sp. ST1, a newly identified potato endophyte isolated from long-term maintained tissue culture plants and detected in field-grown potato. Strain ST1 efficiently colonized internal potato tissues and spread to aboveground organs, likely through the xylem, while maintaining its cellular morphology within the host. Transcriptomic analyses revealed adaptation to both root exudates and the endophytic environment, including shifts in carbon utilization, reduced expression of chemotaxis-associated genes, activation of secretion and host-interaction systems, and regulation of oxidative stress responses. In parallel, ST1-colonized plants exhibited modified root architecture consistent with improved nutrient acquisition and water use, as well as increased tolerance to potato virus Y (PVY). Strain ST1 induced plant transcriptional responses associated with microbe-triggered immunity, although at relatively mild levels consistent with a mutualistic interaction. Together, these findings provide insight into the mechanisms underlying the establishment and maintenance of a stable long-term endophytic association between bacteria and potato plants, while highlighting its contribution to plant growth promotion and stress resilience. </p>