Bacillus G7 improves adaptation to salt stress in Olea europaea L. plantlets enhancing Water Use efficiency and preventing oxidative stress

Plants are naturally endowed with adaptative mechanisms to overcome environmental changing conditions that enable them to grow and survive in adverse conditions. In addition to these mechanisms, plants retrieve additional help from the surrounding microbiome, especially beneficial bacterial strains (PGPB) that contribute to plant fitness modulating plant physiology to fine-tune adaptation to environmental changes. The aim of this study was to explore the effects of a Bacillus strain G7 to modulate the adaptive mechanisms of Olea europaea plantlets to high saline conditions, exploring changes at the physiological, metabolic and gene expression levels. Net carbon fixation and water use efficiency (WUE) were significantly improved, resulting in significant increases in osmolytes and antioxidants while ROS scavenging enzymes were not affected, suggesting a lower oxidative stress, also supported by the high energy dissipation observed. The ABA-mediated pathway was strongly stimulated as ABA synthesis and ABA-sensing related genes were overexpressed together with a strong inhibition of repressors of ABA-response elements, as revealed by the transcriptome analysis. All these results reveal the multitargeted improvement of plant metabolism under salt stress by Bacillus G7, which allows growth under water limitation conditions, an excellent trait to develop biofertilizers for agriculture under harsh conditions.