H OH metabolites OH Review Plant Responses to Abiotic Stresses and Rhizobacterial Biostimulants: Metabolomics and Epigenetics Perspectives Motseoa M. Lephatsi 1 , Vanessa Meyer 2 , Lizelle A. Piater 1 , Ian A. Dubery 1 and Fidele Tugizimana 1,3,* 1 Department of Biochemistry, University of Johannesburg, Auckland Park, Johannesburg 2006, South Africa;
[email protected] (M.M.L.);
[email protected] (L.A.P.);
[email protected] (I.A.D.) 2 School of Molecular and Cell Biology, University of the Witwatersrand, Private Bag 3, WITS, Johannesburg 2050, South Africa;
[email protected] 3 International Research and Development Division, Omnia Group, Ltd., Johannesburg 2021, South Africa * Correspondence:
[email protected]; Tel.: +27-011-559-7784 Abstract: In response to abiotic stresses, plants mount comprehensive stress-specific responses which mediate signal transduction cascades, transcription of relevant responsive genes and the accumulation of numerous different stress-specific transcripts and metabolites, as well as coordinated stress-specific biochemical and physiological readjustments. These natural mechanisms employed by plants are however not always sufficient to ensure plant survival under abiotic stress conditions. Biostimulants such as plant growth-promoting rhizobacteria (PGPR) formulation are emerging as novel strategies for improving crop quality, yield and resilience against adverse environmental conditions. However, to successfully formulate these microbial-based biostimulants and design efficient application programs, the understanding of molecular and physiological mechanisms that govern biostimulant-plant interactions is imperatively required. Systems biology approaches, such as Citation: Lephatsi, M.M.; Meyer, V.; metabolomics, can unravel insights on the complex network of plant-PGPR interactions allowing for Piater, L.A.; Dubery, I.A.; Tugizimana, the identification of molecular targets responsible for improved growth and crop quality.