Biocontrol of Strawberry Powdery Mildew by Bacillus altitudinis DXHS: Mechanistic Insights from Transcriptome Analysis

Strawberry powdery mildew (SPM), caused by Podosphaera aphanis , severely reduces strawberry yield and quality. Due to the pathogen's obligate parasitism, the screening of biocontrol bacteria is challenging, and effective strains remain scarce. In this study, we isolated a novel strain, Bacillus altitudinis DXHS, exhibiting strong control efficacy against SPM. It had abundant gene clusters for secondary metabolite biosynthesis by genomic analysis, including lichenysin, siderophores, and terpene. Strawberry leaves treated with DXHS showed a 77.05% reduction in SPM incidence versus the infected control, which was the first report of B. altitudinis controlling SPM. Transcriptomic analysis of strawberry leaves showed that 3,722 differentially expressed genes (DEGs) were upregulated and 1,729 DEGs were downregulated in the DXHS group compared to SPM group. GO enrichment analysis showed that these DEGs were significantly enriched in biological processes including defense response and the jasmonic acid (JA) signaling pathway. KEGG pathway analysis indicated that the DEGs were enriched in pathways including plant-pathogen interaction, MAPK signaling pathway, and plant hormone signal transduction. Furthermore, GSEA demonstrated a significant enrichment and upregulation of the MAPK signaling pathway. The qPCR validation confirmed significant upregulation of key genes, including MPK3 , MPK6 , PR1 , and ERF1 . These results suggest that the DXHS strain may activate the salicylic acid (SA), JA, and ethylene (ET) pathways in strawberry leaves, enhancing resistance to SPM. These findings provide insights into the molecular mechanism underlying the resistance induced by B. altitudinis DXHS against SPM and the application of DXHS strain in the biological control of strawberry diseases.