Abstract
Microbial plant biostimulants have been successfully applied to improve plant growth, stress resilience and productivity. However, the mechanisms of action of biostimulants are still enigmatic, which is the main bottleneck for the fully realization and implementation of biostimulants into the agricultural industry. Here, we report the elucidation of a global metabolic landscape of maize (Zea mays L) leaves in response to a microbial biostimulant, under well-watered and drought conditions. The study reveals that the increased pool of tricarboxylic acid (TCA) intermediates, alterations in amino acid levels and differential changes in phenolics and lipids are key metabolic signatures induced by the application of the microbial-based biostimulant. These reconfigurations of metabolism gravitate toward growth-promotion and defense preconditioning of the plant. Furthermore, the application of microbial biostimulant conferred enhanced drought resilience to maize plants via altering key metabolic pathways involved in drought resistance mechanisms such as the redox homeostasis, strengthening of the plant cell wall, osmoregulation, energy production and membrane remodeling. For the first time, we show key molecular events, metabolic reprogramming, activated by a microbial biostimulant for plant growth promotion and defense priming. Thus, these elucidated metabolomic insights contribute to ongoing efforts in decoding modes of action of biostimulants and generating fundamental scientific knowledgebase that is necessary for the development of the plant biostimulants industry, for sustainable food security.
Highlights
Drought stress is one of the major abiotic stresses constraining global crop production (Lesk et al, 2016)
The microbial biostimulant used in this study was a consortium of five Bacillus strains, referred hereafter as plant growth-promoting rhizobacteria (PGPR)
The PGPR-induced metabolic alterations spanned a wide spectrum of metabolite classes (Figure 1) including phenolic compounds, lipids, organic acids, hormones and amino acids
Summary
Drought stress is one of the major abiotic stresses constraining global crop production (Lesk et al, 2016). Some of the currently elucidated molecular changes underlying microbial-induced systemic resistance against drought stress include (i) the production of phytohormones, siderophores, volatiles and osmolytes, (ii) the enhanced antioxidant defense system and (iii) 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity and exopolysaccharides (EPS) production (Ahemad and Kibret, 2014; Vurukonda et al, 2016; Prasad et al, 2017; Bhat et al, 2019) These reported events are a tip of an iceberg in regards to cellular and molecular phenomenology, metabolic profiles and fluxes that represent the integrated output of the molecular machinery and biochemical processes, activated by microbial biostimulants for plant growth promotion and stress resilience. Such insight provides a framework for mechanistic prediction and understanding microbial biostimulant-induced physiological changes in crop plants, under drought conditions; a key necessary step for the development of the plant biostimulants industry, for sustainable food security
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