Abstract
Drought tolerance of plants such as tomato or pepper can be improved by their inoculation with rhizobacteria such as Microbacterium sp. 3J1. This interaction depends on the production of trehalose by the microorganisms that in turn modulate the phyto-hormone profile of the plant. In this work we describe the characterization of metabolic changes during the interaction of pepper plants with Microbacterium sp. 3J1 and of the microorganism alone over a period of drought. Our main findings include the observation that the plant responds to the presence of the microorganism by changing the C and N metabolism based on its glutamine and α-ketoglutarate content, these changes contribute to major changes in the concentration of molecules involved in the balance of the osmotic pressure. These include sugars and amino-acids; the concentration of antioxidant molecules, of metabolites involved in the production of phytohormones like ethylene, and of substrates used for lignin production such as ferulic and sinapic acids. Most of the altered metabolites of the plant when inoculated with Microbacterium sp. 3J1 in response to drought coincided with the profile of altered metabolites in the microorganism alone when subjected to drought, pointing to a response by which the plant relies on the microbe for the production of such metabolites. To our knowledge this is the first comparative study of the microbe colonized-plant and microbe alone metabolomes under drought stress.
Highlights
Drought negatively affects the physiology and biochemistry of plants
The presence of Microbacterium sp. 3J1-Green Fluorescent Protein (GFP) in root tissues of the plant under water stressed and non-stressed plants, was determined by confocal fluorescent microscopy identifying the microorganisms inside the root tissues, showing that the microbial strain efficiently colonized the rhizosphere and pepper roots and that it was intimately associated with the plant since it was isolated from the interior of root and shoot tissues of inoculated plants (Figure 1B)
Our results indicate that production of osmoprotectants and antioxidants may collectively mediate enhanced resistance to water deficit in pepper plants when inoculated with Microbacterium sp. 3J1
Summary
Drought negatively affects the physiology and biochemistry of plants. Many mechanisms have been described in response to drought which include the synthesis of compatible solutes for example, amino acids such as proline and betaine. An increase in trehalose concentration, in addition to its xeroprotective effects, modulates the phytohormone profile of the plant (Rodriguez-Salazar et al, 2009; Yang et al, 2010; Lunn et al, 2014) This accumulation of compatible solutes is normally accompanied by the accumulation of antioxidant molecules to maintain cell turgor pressure, and to protect essential biomolecules from the cell, including membranes and enzymes from oxidative damage (Gill and Tuteja, 2010; Krasensky and Jonak, 2012; Gagné-Bourque et al, 2016). Other mechanisms proposed for the protection of plants against drought includes the so-called induced systemic tolerance (IST) process This process involves the modification of phytohormonal profiles, production of antioxidant defense mechanisms, the use of bacterial exopolysaccharides (EPS), and those associated with accumulation of several xeroprotectants such as sugars, amino acids, and polyamines by associated microorganisms. The production of heatshock proteins (HSPs), dehydrins, and volatile organic compounds (VOCs) are involved in the acquisition of drought tolerance (Kaushal and Wani, 2016; Vurukonda et al, 2016)
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