Assessing xylem endophytes interplay with Xylella fastidiosa or Brenneria salicis

Xylella fastidiosa and Brenneria salicis are xylem-specialist phytopathogens that frequently cause severe decline in host plants. However, some infected plants remain asymptomatic, and the factors underlying this dual symptomatology are not fully understood. Emerging evidence suggests that interactions between pathogenic bacteria and the endophytic xylem microbiota may influence disease outcomes. While endophytes are known to contribute to plant health, the mechanisms of their protective effects remain largely unexplored. This study investigates how xylem-associated endophytes interact with X. fastidiosa and B. salicis to inhibit their colonization and mitigate symptom development. Leveraging insights into the interaction between Salicaceae plants and these pathogens, over 400 bacterial endophytes were isolated, with several identified as potential biocontrol candidates. The composition of the isolated microbiome was completed with some metagenomic amplification. Then, simple confrontation assays were performed to evaluate interactions between these endophytes and X. fastidiosa KLN59.3 or B. salicis LMG2698. Promising isolates exhibiting inhibitory effects underwent further characterization and genome sequencing. Some of these strains are being transformed to express fluorescent proteins, enabling visualization of their growth, propagation, and interactions with pathogens within xylem vessels. Co-inoculation experiments using both Salicaceae hosts and Nicotiana tabacum serve as models for understanding these dynamics. This work sheds light on the role of xylem endophytes in plant-pathogen interactions and highlights their potential as biocontrol agents to manage diseases caused by xylem-inhabiting phytopathogens.