Systems-level Plant Responses Reveal Pseudomonas-Mediated Growth Promotion in Brachypodium Under Nitrogen Limitation

Plant molecular adaptation to plant growth promoting bacteria (PGPB) under nutrient stress remains unclear, yet is essential for advancing PGPB use in agriculture. The model grass Brachypodium dystachion was studied together with Pseudomonas koreeensis (Pk) at two nitrogen (N) conditions. Non-invasive shoot phenotyping showed an immediate response to low-N, while beneficial effects of Pk became quantifiable after day 19. Increased N content in inoculated plants, along with Pks ability to grow on N-free media, suggests bacterial N contribution at deficient N. In low-N conditions, Pk-inoculated plants showed 33.2% more N than uninoculated controls and biomass comparable to high-N plants. Pk had no effect under sufficient N. Proteomics and lipidomics revealed that lipid profiles were primarily shaped by N availability, while protein abundance responded to both Pk and N status. Inoculated low-N plants displayed protein profiles resembling those of high-N controls, with some distinct exceptions. The plant-microbe interaction is dynamic and developed over 3 weeks, leading to increased biomass and N content. Root proteins strongly induced by Pk under low-N included lipid degradation enzymes, N transporters, and regulatory proteins, suggesting a coordinated remodelling of energy metabolism supporting whole-plant biomass and increased abundance of N uptake proteins.