Vertically transmitted seed core endophytes enhance the drought tolerance of Ambrosia artemisiifolia

Seed endophytes play a pivotal role in shaping plant microbiota, with certain species being vertically transmitted throughout the plant's life history. Nevertheless, their transmission patterns and contributions to drought adaptation remain poorly understood. In this study, through comparative analysis of microbial communities in seeds and in vitro plantlets from five geographic populations, Pseudomonas and Bacillus were identified as vertically transmitted core endophytes. Analysis of endophytic communities in leaves and roots of plants grown in a common garden further revealed that these genera not only dominated the microbiota but also served as potential keystone taxa. Moreover, pot experiments demonstrated that these genera remained dominant under drought. Representative culturable isolates associated with core vertically transmitted OTUs, including Pseudomonas benzopyrenica and Bacillus cereus, carried multiple antioxidant-related genes based on whole-genome sequencing, and qRT-PCR analysis further showed that most of these genes were upregulated under drought stress. The pot experiment revealed that both strains enhance plant drought tolerance, with altered NCED expression associated with modulated ABA levels, and changes in GST, SOD2, and CAT expression correlated with reduced accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in inoculated plants. These findings advance our understanding of the role of vertically transmitted core endophytes in the adaptation of invasive plants and offer new perspectives for microbiome-based management strategies.