Amelioration of Soybean Plant from Saline-Induced Condition by Exopolysaccharide Producing <i>Pseudomonas</i>-Mediated Expression of High Affinity K⁺-transporter (HKT1) Gene

Abstract

There is a consensus that soil salinization causes decreased agricultural production. Several plants may adapt to survive under high salt stress wherein glycophytes fail to grow. Among transporters in plants, the sodium transporter, also known as high-affinity K + -transporter (HKT1) that comes under the HKT gene family, is involved in uptake of sodium through the roots and its recirculation from shoot to root. In the present study, we have examined the role of transporter HKT1 in soybean plants upon addition of 200 mM NaCl and treatment with Pseudomonas sp. strain AK-1. It is reported that HKT1 is permeable to K + /Na + and systemically alleviates salinity stress through upregulation of gene expression in shoots and down-regulation in roots. Higher transcription levels in shoot recirculate Na + from shoot xylem to root phloem whereas lower transcription levels in root do not allow sodium to enter the plants through root cells. We have also examined role of exopolysaccharide (EPS) produced by strain AK-1 which helps in the binding of free Na + from soil and thus makes Na + unavailable to the soybean plants. Strain with EPS showed decrease in electrical conductivity of soil from 1.1 to 0.9 dS/m in the presence of 200 mM NaCl. In conclusion, treatment with Pseudomonas sp. strain AK-1 exhibits significant rise in shoot/root length, number of lateral roots, shoot/root fresh weight and decreased Na + /K + ratio under salinity stress.

The Effects of Plant-Associated Bacterial Exopolysaccharides on Plant Abiotic Stress Tolerance

“…Plant responses to salt stress include morphological, physiological, and biochemical changes aimed to exclude or restrict the uptake of toxic ions, maintain osmotic balance, and prevent damage to the photosynthetic process [ 41 , 42 , 43 ]. Certain strains of PGPR associated with plant roots are able to induce these changes through a variety of mechanisms, including plant hormones production and modulation [ 44 , 45 , 46 , 47 ], activation of stress-responsive genes [ 48 , 49 ], osmolytes production and osmotic adjustment [ 12 , 13 ], enzyme antioxidant activation [ 48 ], the release of volatile organic compounds [ 50 , 51 ] and bacterial exopolysaccharide production [ 52 , 53 , 54 ].…”

“…In this sense, several studies have demonstrated the beneficial effect of EPS to alleviate salt stress by sodium chelation in the soil, which makes Na + inaccessible to plant roots ( Table 1 ). For instance, Kasotia et al [ 54 ] described that EPS produced by Pseudomonas sp. AK-1 were able to bind free Na + from the soil, making Na + unavailable to soybean and maintain normal plant growth up to 200 mM NaCl.…”

Epsc Involved in the Encoding of Exopolysaccharides Produced by Bacillus amyloliquefaciens FZB42 Act to Boost the Drought Tolerance of Arabidopsis thaliana

“…For instance, in soybean plants exposed to salinity stress, the exopolysaccharides generated by certain Pseudomonas spp. act to reduce the translocation of Na + ions from the soil into the root [30]. Consortia of PGPR and their respective exopolysaccharides have been suggested as conferring a greater benefit with respect to drought tolerance compared with inoculation using PGPR alone [31].…”

When Salt Meddles Between Plant, Soil, and Microorganisms

“…The kind of EPS produced by Pseudomonas spp. (Kasotia et al, 2016), and Bacillus spp. (Amna et al, 2019) helped in the binding of free Na + from the soil, thus making Na + unavailable to the soybean and wheat plants, respectively.…”