Abstract
Drought stress is an alarming constraint to plant growth, development, and productivity worldwide. However, plant-associated bacteria, fungi, and viruses can enhance stress resistance and cope with the negative impacts of drought through the induction of various mechanisms, which involve plant biochemical and physiological changes. These mechanisms include osmotic adjustment, antioxidant enzyme enhancement, modification in phytohormonal levels, biofilm production, increased water and nutrient uptake as well as increased gas exchange and water use efficiency. Production of microbial volatile organic compounds (mVOCs) and induction of stress-responsive genes by microbes also play a crucial role in the acquisition of drought tolerance. This review offers a unique exploration of the role of plant-associated microorganisms—plant growth promoting rhizobacteria and mycorrhizae, viruses, and their interactions—in the plant microbiome (or phytobiome) as a whole and their modes of action that mitigate plant drought stress.
Highlights
More than 700 million people in the world are severely affected by food insecurity according to the Food Security Information Network and Global Network Against Crises (2020), and this rate is likely to increase if the issues causing food insecurity are not addressed
Many enzymes that participate in photosynthesis, such as ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase), NADP-malic enzyme (NADP-ME), fructose-1,6-bisphosphatase (FBPase) and pyruvate orthophosphate dikinase
The most studied plant associated organisms are plant-growth promoting rhizobacteria (PGPR) (Ngumbi and Kloepper, 2016; Martins et al, 2018b; Ullah et al, 2019), mycorrhizal fungi (Quiroga et al, 2017; Zhang et al, 2017; Diagne et al, 2020), and viruses (Xu et al, 2008; Dastogeer et al, 2018). We focused on these three drought stress metigators and explained the modes of action through which they help plants mitigate drought stress (Figure 1)
Summary
More than 700 million people in the world are severely affected by food insecurity according to the Food Security Information Network and Global Network Against Crises (2020), and this rate is likely to increase if the issues causing food insecurity are not addressed. Grover et al (2014) found that treatment of Sorghum bicolor with Bacillus spp. strains KB122, KB129, KB133, and KB142 resulted in increased shoot length, root dry biomass, relative water content, sugar, chlorophyll, soil moisture content, and proline content, thereby improving sorghum seedling growth and health under drought stress conditions.
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