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

• Published in: The Plant journal : for cell and molecular biology Vol. 112; no. 2; pp. 322 - 338
• Main Authors: Han, Qing‐Qing, Wang, Yong‐Ping, Li, Jian, Li, Jing, Yin, Xiao‐Chang, Jiang, Xing‐Yu, Yu, Min, Wang, Suo‐Min, Shabala, Sergey, Zhang, Jin‐Lin
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01-10-2022
• Subjects: Deprivation; Efflux; Extrusion; Halophytes; HKT1;5; K+ deprivation; Na+ exclusion; Potassium; Puccinellia; Puccinellia tenuiflora; Saline soils; Salinity; Salinity effects; Salinity tolerance; salt stress; Salt tolerance; Selectivity; Sodium; Soil salinity; SOS1; Transport processes; Xylem; Yeasts
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.15946

SUMMARY
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 that P. tenuiflora possesses stronger selectivity for K+ than for Na+; however, the mechanistic basis of this phenomenon 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 that PutHKT1;5 possessed Na+ transporting capacity and was highly selective for Na+ over K+. PutSOS1 was located at the plasma membrane and operated as a 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 upregulated 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, which was consistent with root Na+ efflux. The transcript levels of root PutHKT2;1 and PutAKT1 were downregulated 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/channel (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.
Significance Statement
P. tenuiflora is considered an important model halophyte due to its strong salt tolerance and close genetic relationship with cereals. Here, We aimed to elucidate the coordinated physiological and molecular mechanism for P. tenuiflora adapt to severe salinity and K+ starvation conditions.