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Drought is a critical factor limiting the productivity of legumes worldwide. Legumes can enter into a unique tripartite symbiotic relationship with root-nodulating bacteria of genera Rhizobium, Bradyrhizobium, or Sinorhizobium and colonization by arbuscular mycorrhizal fungi (AMF). Rhizobial symbiosis provides nitrogen necessary for growth. AMF symbiosis enhances uptake of diffusion-limited nutrients such as P, Zn, Cu, etc., and also water from the soil via plant-associated fungal hyphae. Rhizobial and AMF symbioses can act synergistically in promoting plant growth and fitness, resulting in overall yield benefits under drought stress. One of the approaches that rhizobia use to survive under stress is the accumulation of compatible solutes, or osmolytes, such as trehalose. Trehalose is a non-reducing disaccharide and an osmolyte reported to accumulate in a range of organisms. High accumulation of trehalose in bacteroids during nodulation protects cells and proteins from osmotic shock, desiccation, and heat under drought stress. Manipulation of trehalose cell concentrations has been directly correlated with stress response in plants and other organisms, including AMF. However, the role of this compound in the tripartite symbiotic relationship is not fully explored. This review describes the biological importance and the role of trehalose in the tripartite symbiosis between plants, rhizobia, and AMF. In particular, we review the physiological functions and the molecular investigations of trehalose carried out using omics-based approaches. This review will pave the way for future studies investigating possible metabolic engineering of this biomolecule for enhancing abiotic stress tolerance in plants.

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Black gram is one of the most indispensable components of the world food basket and the growth and health of the crop get influenced by biotic and abiotic factors. Beneficial phyto-microbes are one among them that influence the crop growth, more particularly the seed borne microbes are comparatively beneficial, that they pass from generation to generation and are associated with the plants from establishment to development. In the present study, twenty seed-borne yeasts were characterized and tested for growth promotion of black gram and their antagonism against black gram phytopathogens. Two yeasts, Pichia kudriavzevii POY5 and Issatchenkia terricola GRY4, produced indole acetic acid (IAA), siderophore, 1-amino cyclopropane-1-carboxylic acid deaminase (ACCD), and plant defense enzymes. They solubilized phosphate and zinc and fixed atmospheric nitrogen. Inoculation of these two yeast isolates and Rhizobium BMBS1 improved the seed germination, physiological parameters and yield of black gram. Inoculation of Rhizoctonia solani-challenged plants with plant growth-promoting yeasts, resulted in the synthesis of defense-related enzymes such as peroxidases (POD), chitinases, catalase (CAT), and polyphenol oxidases (PPO). Thus, the seed-borne yeasts, Pichia kudriavzevii POY5 and Issatchenkia terricola GRY4, could be used as plant probiotics for black gram.

Delineation of mechanistic approaches of rhizosphere microorganisms facilitated plant health and resilience under challenging conditions. 3 Biotech, 12(3), 57.