Hydrogen Peroxide Metabolism in Interkingdom Interaction Between Bacteria and Wheat Seeds and Seedlings

In endophytes, the abundance of genes coding for enzymes processing reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂), argues for a crucial role of ROS metabolism in plant-microbe interaction for plant colonization. Here, we studied H₂O₂ metabolism of bread wheat (Triticum aestivum L.) seeds and their microbiota during germination and early seedling growth, the most vulnerable stages in the plant life cycle. Treatment with hot steam diminished the seed microbiota, and these seeds produced less extracellular H₂O₂ than untreated seeds. Using a culture-dependent approach, Pantoea and Pseudomonas genera were the most abundant epiphytes of dry untreated seeds. Incubating intact seedlings from hot steam-treated seeds with Pantoea strains triggered H₂O₂ production, whereas Pseudomonas strains dampened H₂O₂ levels, attributable to higher catalase activities. The genus Pantoea was much less represented among seedling endophytes than genus Pseudomonas, with other endophytic genera, including Bacillus and Paenibacillus, also possessing high catalase activities. Overall, our results show that certain bacteria of the seed microbiota are able to modulate the extracellular redox environment during germination and early seedling growth, and high catalase activity is proposed as a key trait of seed endophytes.