Transcriptional Response of <i>Magnaporthe oryzae</i> Toward Barley Microbiome-Derived Bacteria

The composition of the plant microbiome is shaped not only by the host plant and abiotic environmental factors, but also by intermicrobial cooperation and competition. Plant pathogens, therefore, must remain competitive within the microbiome to establish themselves within their host niche. <i>Magnaporthe oryzae</i>, the blast disease-causing ascomycete fungus, can infect economically important hosts including rice, barley, and wheat. We sought to identify barley-associated bacteria able to antagonize <i>M</i>. <i>oryzae</i> and to characterize the fungal transcriptional responses following confrontation to reveal antimicrobial self-defense mechanisms. From a library of 25 barley-associated bacteria, two strains were identified as moderate and strong antagonists. Through RNA-seq, we demonstrate large-scale transcriptional changes in <i>M</i>. <i>oryzae</i> during their confrontation. Common responses to both strains included an overrepresentation of genes encoding drug efflux transporters, hydrolases, signaling components, DNA repair, and oxidative stress responses. This indicates that <i>M. oryzae</i> prioritizes stress adaptation and detoxification. We did not observe a significant increase in secreted proteins of <i>M</i>. <i>oryzae</i> as part of the common response. However, significant strain-specific changes were observed, indicating that, independent of host plant, specific microbial antagonists are perceived by <i>M</i>. <i>oryzae</i>, leading to altered secretome profiles. Understanding these adaptive strategies provides insight into antimicrobial resistance mechanisms with respective parallels to drug- and fungicide-resistance mechanisms in the medical and agricultural context. Additionally, our study provides potential targets on the plant pathogen side to weaken its fitness within the plant microbiome. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.