Title: The mechanistic basis of sodium exclusion in Puccinellia tenuiflora under conditions of soil salinity and potassium deprivation

Authors: Qing-Qing Han, Yong-Ping Wang, Jian Li, Jing Li, Xiao-Chang Yin, Xing-Yu Jiang, Min Yu, Suo-Min Wang, Sergey Shabala*, Jin-Lin Zhang*

Journal: The Plant Journal

Impact Factor: IF₂₀₂₁ = 7.09

Abstract: Soil salinity is a significant threat to global agriculture. Understanding salt-exclusion mechanisms in halophyte species may be instrumental in improving salt tolerance in crops. Puccinellia tenuiflora is a typical salt-excluding halophytic grass often found in potassium-deprived saline soils. Our previous work showed P. tenuiflora possesses stronger selectivity for K⁺ over Na⁺; however, the mechanistic basis of this process remained elusive. Here, P. tenuiflora PutHKT1;5 was cloned and the functions of PutHKT1;5 and PutSOS1 were characterized using heterologous expression systems. Yeast assays showed PutHKT1;5 possessed Na⁺ transporting capacity and was highly selective for Na⁺ over K⁺. PutSOS1 was located at the plasma membrane and operated as Na⁺/K⁺ exchanger, with much stronger Na⁺ extrusion capacity than its homolog from Arabidopsis. PutHKT2;1 mediated high-affinity K⁺ and Na⁺ uptake and its expression levels were up-regulated by mild salinity and K⁺ deprivation. Salinity-induced changes of root PutHKT1;5 and PutHKT1;4 transcript levels matched the expression pattern of root PutSOS1 that was consistent with root Na⁺ efflux. The transcript levels of root PutHKT2;1 and PutAKT1 were down-regulated by salinity. Taken together, these findings demonstrate that the functional activity of PutHKT1;5 and PutSOS1 in P. tenuiflora roots is fine-tuned under saline conditions as well as by operation of other ion-transporters (PutHKT1;4, PutHKT2:1 and PutAKT1). This leads to the coordination of radial Na⁺ and K⁺ transport processes, their loading to the xylem, or Na⁺ retrieval and extrusion under conditions of mild salinity and / or K⁺ deprivation.

Linkage: https://onlinelibrary.wiley.com/doi/10.1111/tpj.15946