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

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 ischolar_mains and its recirculation from shoot to ischolar_main. 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 ischolar_mains. Higher transcription levels in shoot recirculate Na⁺ from shoot xylem to ischolar_main phloem whereas lower transcription levels in ischolar_main do not allow sodium to enter the plants through ischolar_main 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/ischolar_main length, number of lateral ischolar_mains, shoot/ischolar_main fresh weight and decreased Na⁺/K⁺ ratio under salinity stress.