Comparisons in functions of HKT1;5 transporters between Hordeum marinum and Hordeum vulgare in responses to salt stress
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Sea barley (Hordeum marinum) is more salt tolerant than barley (Hordeum vulgare). In our previous study, H. marinum accession H559 showed the superior salt tolerance and K+/Na+ homeostasis than barley cultivar Golden Promise under 400 mM NaCl. However, the molecular mechanism underlying the difference of salt tolerance between the two species remains to be revealed. Here, we characterized a homolog of HvHKT1;5 transporter in sea barley, HmHKT1;5, and compared their functions in salt tolerance. Like HvHKT1;5, HmHKT1;5 also encodes a plasma membrane protein, which is mainly expressed in roots. The expression of both genes was induced by salt stress, but HmHKT1;5 had less increase than HvHKT1;5. When expressed in Xenopus laevis oocytes, both HmHKT1;5 and HvHKT1;5 were permeable to only Na+, but the transport affinity of HmHKT1;5 was lower than that of HvHKT1;5. Moreover, when each of the two genes was introduced into rice cv. Nipponbare, both the HvHKT1;5 and HmHKT1;5 transgenic lines showed greater Na+ uptake than the wild-types, resulting in enhancement of salt stress sensitivity. Besides, the introduction of HvHKT1;5 also increased Na+ translocation from roots to shoots in rice, while the introduction of HmHKT1;5 did not. The results indicate that HvHKT1;5 is involved in Na+ uptake and translocation from roots to shoots and HmHKT1;5 is only involved in Na+ uptake, and the uptake ability of HmHKT1;5 for Na+ is much weaker than that of HvHKT1;5. These findings partially reveal the reasons why H. marinum has higher salt tolerance than H. vulgare.
KeywordsSalt tolerance High affinity HKT transporters Na+ loading Ion homeostasis
This study was supported by National Natural Science Foundation of China (31620103912, 31771685), China Agriculture Research System (CARS-05) and Jiangsu Collaborative Innovation Centre for Modern Crop Production (JCIC-MCP). We thank Dr. JM Xu (Zhejiang University, China) for elements analysis.
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