Overexpression of AtNHX1 increases leaf potassium content by improving enrichment capacity in tobacco (Nicotiana tabacum) roots

The NHX1 gene encodes a Na+/H+ antiporter located in the tonoplast membrane, which plays critical role in regulating plant salt tolerance. It is also involved in the uptake and accumulation of K in plants; however, its precise mechanism is unknown. In this research, we elucidated the physiological basis underlying the increases in K content induced by NHX1. We evaluated main agronomic traits, leaf K content, K+ uptake kinetics, and root morphological and physiological characteristics from field-planted and hydroponic plants. We included a wild-type tobacco (Nicotiana tabacum) variety (K326) and three transgenic tobacco lines (NK7, NK9, NK10) that overexpress AtNHX1 from Arabidopsis thaliana. Results demonstrated that the agronomic performance of the AtNHX1-overexpressing tobacco lines was similar to K326 in field and hydroponic settings. The three AtNHX1-overexpressing tobacco lines had significantly higher leaf K contents than K326. Under hydroponic condition, enhanced K uptake capacity and a larger maximum K uptake rate were seen in AtNHX1-overexpressing tobacco lines. AtNHX1-overexpressing lines also exhibited significantly superior root morphological and physiological traits relative to K326, including root biomass, root volume, absorption area, root activity, cation exchange capacity, soluble protein content, and H+-ATPase activity. Overexpression of AtNHX1 in tobacco significantly improves the K uptake and accumulation. Therefore, leaf K content greatly increased in these transgenic lines in the end. Our findings strongly suggest that AtNHX1 overexpression increased leaf K content by boosting the capacity of enriching K in tobacco roots, thereby advancing the understanding of the function of AtNHX1.