Molecular mechanisms of Pseudomonas-enhanced plant performance in Brachypodium under limited nitrogen

Abstract

While the world population is increasing, the use of nitrogenous fertilizers has become obligatory to increase yields to meet the global food demand. Overuse of synthesized N fertilizers does not only negatively impact the environment during its energy intensive Haber-Bosch process, but also affects ground water bodies due to nitrate leaching losses and elevated N2O emissions. Improved use of N by crops may be achieved with N-fixing plant-growth promoting bacteria (PGPB). <br /> In this thesis, I investigated the temporally resolved morphological and biochemical responses of <em>Brachypodium distachyon</em> to inoculation with <em>Pseudomonas koreensis</em> a bacterial species previously shown to harbor plant growth-promoting properties. This investigation was conducted under different N levels. <em>P. koreensis</em> was tested for its ability to fix N via a ¹⁵N natural abundance approach. Under zero and limited N, inoculated plants have shown trends to a decreased &delta;¹⁵N signature, indicating an additional 14N source. A whole-plant increase in N content was observed in plants grown in limited N conditions when inoculated with <em>P. koreensis</em>, whereas the root C-content was significantly decreased. Limited N supplied plants inoculated with <em>P. koreensis</em> have shown several improvements in morphological parameters, such as (projected) leaf area, fresh weight, dry weight, and lateral root length at 21 days after sowing (DAS). The molecular mechanisms were investigated utilizing proteomics and lipidomics measurements. Inoculated limited N supplied plants have shown a comparable protein profile to sufficient N control plants. The lipid profile primarily responded to the two N levels. Additionally, <em>P. koreensis</em> inoculation altered the abundance of membrane and storage lipids prior to the growth promotion at 19 DAS. <br /> The generated descriptive data have the potential to shape future research to increase our understanding of plant-microbe interactions, leading to a decrease in synthetic N fertilizer production and application.