Abstract
Drought conditions marked by water deficit impede plant growth thus causing recurrent decline in agricultural productivity. Presently, research efforts are focussed towards harnessing the potential of microbes to enhance crop production during drought. Microbial communities, such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) buddy up with plants to boost crop productivity during drought via microbial induced systemic tolerance (MIST). The present review summarizes MIST mechanisms during drought comprised of modulation in phytohormonal profiles, sturdy antioxidant defence, osmotic grapnel, bacterial exopolysaccharides (EPS) or AMF glomalin production, volatile organic compounds (VOCs), expression of fungal aquaporins and stress responsive genes, which alters various physiological processes such as hydraulic conductance, transpiration rate, stomatal conductivity and photosynthesis in host plants. Molecular studies have revealed microbial induced differential expression of various genes such as ERD15 (Early Response to Dehydration 15), RAB18 (ABA-responsive gene) in Arabidopsis, COX1 (regulates energy and carbohydrate metabolism), PKDP (protein kinase), AP2-EREBP (stress responsive pathway), Hsp20, bZIP1 and COC1 (chaperones in ABA signalling) in Pseudomonas fluorescens treated rice, LbKT1, LbSKOR (encoding potassium channels) in Lycium, PtYUC3 and PtYUC8 (IAA biosynthesis) in AMF inoculated Poncirus, ADC, AIH, CPA, SPDS, SPMS and SAMDC (polyamine biosynthesis) in PGPR inoculated Arabidopsis, 14-3-3 genes (TFT1-TFT12 genes in ABA signalling pathways) in AMF treated Solanum, ACO, ACS (ethylene biosynthesis), jasmonate MYC2 gene in chick pea, PR1 (SA regulated gene), pdf1.2 (JA marker genes) and VSP1 (ethylene-response gene) in Pseudomonas treated Arabidopsis plants. Moreover, the key role of miRNAs in MIST has also been recorded in Pseudomonas putida RA treated chick pea plants.
Highlights
Escalation in drought incidences as a result of climate change meddles in agricultural productivity as water deficit conditions during drought interfere with the cellular metabolic machinery of plants [1]
Primary physiological criteria examined during water deficit includes relative water content (RWC), stomatal conductance, Chl content, photosynthetic rate (Pn), Fv/Fm and malondialdehyde (MDA) content in leaves [13]
Expression of aquaporin genes GintAQPF1 and GintAQPF1 cloned from R. irregularis was upregulated in cells of cortex and extraradical mycelia of maize roots inoculated by arbuscular mycorrhizal fungi (AMF) (G. intraradices), clearly indicating role of AMF aquaporins in enhancing water transport through AMF hyphae to plant
Summary
Escalation in drought incidences as a result of climate change meddles in agricultural productivity as water deficit conditions during drought interfere with the cellular metabolic machinery of plants [1]. Microbes can enhance drought tolerance in plants via microbial induced systemic tolerance (MIST) mechanisms involving various biochemical, physiological and molecular modifications in host plants. Arbuscular mycorrhizal fungi (AMF) inoculation have been observed to increase drought tolerance via maintaining Pn [17], RWC [18,19], MDA content [20], Fv/Fm [21] and gs in host plants [22]. This is primarily accomplished via enhanced hydration status and nutritional profile preserving the cellular turgor and machinery in plants during drought. Microbe Mediated Biochemical and Metabolic Mechanisms to Regulate Oxidative and Osmotic Stress
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