Unveiling Metabolic Crosstalk: Bacillus-Mediated Defense Priming in Pine Needles Against Pathogen Infection

<b>Background/Objectives:</b> Plant growth-promoting rhizobacteria (PGPR), particularly <i>Bacillus</i> spp., are pivotal in enhancing plant defense mechanisms against pathogens. This study aims to investigate the metabolic reprogramming of pine needles induced by <i>Bacillus</i> csuftcsp75 in response to the pathogen <i>Diplodia pinea</i> P9, evaluating its potential as a sustainable biocontrol agent. <b>Methods:</b> Using liquid chromatography-mass spectrometry (LC-MS/MS), we performed a principal component analysis and a cluster analysis to assess the metabolic alterations in treated versus control groups. This study focused on specific metabolites associated with plant defense. <b>Results:</b> Our findings indicate that treatment with <i>Bacillus</i> csuftcsp75 significantly modifies the metabolic profiles of pine needles, leading to notable increases in metabolites associated with flavonoid biosynthesis, particularly phenylpropanoid metabolism, as well as amino acid metabolism pathways. These metabolic changes indicate enhanced systemic acquired resistance (SAR) and induced systemic resistance (ISR), with treated plants exhibiting elevated levels of defense-related compounds such as 5-hydroxytryptophol and oleanolic acid. <b>Conclusions:</b> This study reveals that <i>Bacillus</i> csuftcsp75 enhances defense against pathogen P9 by modulating pine needle metabolism and activating key immune pathways, inducing systemic acquired resistance and induced systemic resistance, offering a natural alternative to chemical pesticides in sustainable agriculture.