A sodium transporter HvHKT1;1 confers salt tolerance in barley via regulating tissue and cell ion homeostasis
2018
Han, Y. (Zhejiang University, Hangzhou (China). Agronomy Department, Key Laboratory of Crop Germplasm Resource of Zhejiang Province) | Yin, S. | Huang, L. | Wu, X. | Zeng, J. | Liu, X. | Qiu, L. | Munns, R. | Chen, Z.H. | Zhang, G.
Our previous studies showed that high salt tolerance in Tibetan wild barley accessions was associated with HvHKT1;1, a member of the high-affinity potassium transporter family. However, molecular mechanisms of HvHKT1;1 for salt tolerance and its roles in Ksup(+)/Nasup(+) homeostasis remain to be elucidated. Functional characterization of HvHKT1;1 was conducted in the present study. NaCl-induced transcripts of HvHKT1;1 were significantly higher in the roots of Tibetan wild barley XZ16 relative to other genotypes, being closely associated with its higher biomass and lower tissue Nasup(+) content under salt stress. Heterologous expression of HvHKT1;1 in Saccharomyces cerevisiae (yeast) and Xenopus laevis oocytes showed that HvHKT1;1 had higher selectivity for Nasup(+) over Ksup(+) and other monovalent cations. HvHKT1;1 was found to be localized at the cell plasma membrane of root stele and epidermis. Knock-down of HvHKT1;1 in barley led to higher Nasup(+) accumulation in both roots and leaves, while overexpression of HvHKT1;1 in salt-sensitive Arabidopsis hkt1-4 and sos1-12 loss-of-function lines resulted in significantly less shoot and root Nasup(+) accumulation. Additionally, microelectrode ion flux measurements and root elongation assay revealed that the transgenic Arabidopsis plants exhibited a remarkable capacity for regulation of Nasup(+), Ksup(+), Casup(2+) and Hsup(+) homeostasis under salt stress. These results indicate that HvHKT1;1 is critical in radial root Nasup(+) transport, which eventually reduces shoot Nasup(+) accumulation. Additionally, HvHKT1;1 may be indirectly involved in retention of Ksup(+) and Casup(2+) in root cells, which also improves plant salt tolerance.
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