Transcriptomic responses of Fusarium oxysporum f. sp. radicis-lycopersici to secreted antimicrobial compounds of Pseudomonas chlororaphis ToZa7.

Pseudomonas chlororaphis ToZa7 is a potential biocontrol agent against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) on tomato. This study investigated the effects of ToZa7's crude secondary metabolites on FORL by combining phenotypic bioassays with the early transcriptomic dynamics of the pathogen, after exposure to crude secreted compounds. In vitro bioassays demonstrated that exposure to the bacterial secretome significantly inhibited mycelial growth, conidiation, conidial germination and germ tube elongation. Transcriptomic analysis revealed a strong antagonistic effect against the pathogen, particularly at 1 h post-treatment, by suppression of essential key processes such as cell wall and cell membrane biosynthesis, conidiation, RNA metabolism, ribosome biogenesis, and DNA replication. Notably, a down-regulation of genes encoding chitin and 1,3-b-glucan synthases, alongside conidiation-specific proteins, directly reflected the observed phenotypic delays. Furthermore, down-regulation of virulence-associated hydrolytic enzymes involved in plant cell wall degradation further indicates a direct effect on the pathogen's infection potential. By 6 h post-treatment, activation of oxidative stress responses and cellular detoxification mechanisms in FORL, suggest a partial adaptive response that was insufficient to overcome the fungal growth inhibition effect. These results provide novel insights into the molecular mechanisms underlying microbial interactions in the tomato rhizosphere and highlight the potential of P. chlororaphis ToZa7 for effective biological control of FORL.