Poly-γ-Glutamic Acid-Induced Assemblage of Root Endophytic Microbiota Enhances Disease Resistance in Chrysanthemum Plants

Plant microbiota composition changes with the environment and host state, suggesting potential for engineering. However, engineering plant microbiomes is promising but currently undeveloped. This study investigated the role of root-associated bacterial microbiomes in poly-γ-glutamic acid (γ-PGA)-induced plant disease resistance. γ-PGA treatment significantly reduced wilt disease caused by Fusarium oxysporum f. sp. chrysanthemi (Foc). Quantitative PCR analysis revealed a 73.2% reduction in Foc abundance in the roots following γ-PGA exposure. However, the disease suppression effect of γ-PGA was notably weakened in sterilized soils or soils treated with bactericide, indicating the essential role of root-associated microbiomes in this process. 16S rRNA gene amplicon sequencing showed that γ-PGA treatments increased the abundance of Proteobacteria, particularly the family Burkholderiaceae, in the roots. Metabolite analysis further indicated that γ-PGA treatment significantly elevated salicylic acid (SA) levels, suggesting that SA played a critical role in the assembly of the root microbiome under γ-PGA treatment. Further experiments confirmed the antagonistic activity and induced systemic resistance (ISR) of Burkholderia sp. against Fusarium wilt. Burkholderia sp. CM72 was found to enhance plant disease resistance through antibiosis and activation of jasmonic acid (JA)-related pathways. In summary, γ-PGA significantly improved plant disease resistance by modulating the SA pathway and promoted the colonization of beneficial microbiota, particularly with Burkholderia sp.