Laminaria extracts and rhizobacteria (Paenibacillus alvei T22) elicit metabolic reprogramming of wheat seedlings: A metabolomics-guided biostimulants mode-of-action discovery for plant growth and defence priming

Plant biostimulants, including seaweed extracts (SWE) and plant growth-promoting rhizobacteria (PGPR), are known to enhance crop performance, while multi-component biostimulants, combining microbial and non-microbial agents, show promise for enhanced plant physiological responses and defence activation, yet their metabolic mechanisms remain enigmatic. This breakthrough study unveils the molecular mechanisms behind biostimulants action -PGPR (Paenibacillus alvei T22), and seaweed extract laminarin (L-1)- in wheat seedlings (Triticum aestivum L.) through comprehensive untargeted metabolomics using ultra-high-performance liquid chromatography coupled to high-definition mass spectrometry (UHPLC-HD-MS) and advanced pathway enrichment analysis. Three distinct metabolic phenotypes were identified: Laminarin (SWE) treatment triggers the modulation of the energy metabolism with maximum energy production, characterised by robust activation of the citric acid (TCA) cycle, and rapid activation of the secondary metabolism through the upregulation of aromatic amino acids (Phenylalanine, Tyrosine, Tryptophan), feeding into the phenylpropanoid pathway. PGPR treatment orchestrates precision defence priming with moderate and controlled activation of the energy metabolism, accompanied by a targeted modulation of secondary metabolism and the phenylpropanoid pathway. Remarkably, combined P. alvei (T22) and laminarin L-1 treatment achieved a metabolic optimisation, a harmonised activation and modulation of both the primary and secondary metabolism, transcending simple additive effects to create genuine metabolic enhancement. These biostimulants fundamentally reprogram plant metabolism through distinct pathway-level mechanisms revealed by metabolic network analysis, unlocking the molecular basis of superior plant performance. These discoveries provide the mechanistic framework for designing next generation biostimulants formulations tailored to specific crop requirements, environmental challenges, and performance targets in precision agriculture, for sustainable agricultural intensification through targeted metabolic reprogramming.