Morpho-Physiological, Root Exudation and Metabolomics Insights on the Single and Combined Effect of Exogenous Strigolactones and Mycorrhiza in Tomato

Strigolactones (SLs) are plant hormones and have recently been characterized for their regulatory roles in plant development and rhizosphere communication, including interactions with arbuscular mycorrhizal fungi (AMF). The present work investigated the single and combined effects of exogenous GR24, an SL analogue, and AMF in tomato plants by assessing their potential synergistic effects on morpho-physiological enhancements and on AMF colonization through root-untargeted metabolomics and root exudate profiling. Specifically, a supervised multi-omics data integration approach has been used to identify the most relevant features correlated with treatments. Although the effect of AMF appeared to be hierarchically prevalent, GR24 provided significant effects at all levels when applied alone or combined with AMF. Noteworthy, the combination of GR24 and AMF delivered synergistic effects on morphological and photosynthetic traits with reduced energy loss in photosystem II (PSII) and increased chlorophyll content, and provided distinctive metabolic profiles compared to the single treatments. Mostly in the presence of the GR24 + AMF treatment, a positive modulation of N-containing compounds, phenylpropanoids, terpenes, and phytoalexins and an adjustment of phytohormones like abscisic acid, brassinosteroid, cytokinin, and jasmonate crosstalk was observed. Moreover, the exudation signatures were consistently distinctively shaped, enriched in flavonoids and amino acids. Finally, the multi-omics data integration underlined a positive correlation between the roots and root exudate datasets, with high discriminatory potential of the selected features among the treatments.