Mapping of HKT1;5 Gene in Barley Using GWAS Approach and Its Implication in Salt Tolerance Mechanism

Abstract

Sodium (Na+) accumulation in the cytosol will result in ion homeostasis imbalance and toxicity of transpiring leaves. Studies of salinity tolerance in the diploid wheat ancestor Triticum monococcum showed that HKT1;5-like gene was a major gene in the QTL for salt tolerance, named Nax2. In the present study, we were interested in investigating the molecular mechanisms underpinning the role of the HKT1;5 gene in salt tolerance in barley (Hordeum vulgare). A USDA mini-core collection of 2,671 barley lines, part of a field trial was screened for salinity tolerance, and a Genome Wide Association Study (GWAS) was performed. Our results showed important SNPs that are correlated with salt tolerance that mapped to a region where HKT1;5 ion transporter located on chromosome four. Furthermore, sodium (Na+) and potassium (K+) content analysis revealed that tolerant lines accumulate more sodium in roots and leaf sheaths, than in the sensitive ones. In contrast, sodium concentration was reduced in leaf blades of the tolerant lines under salt stress. In the absence of NaCl, the concentration of Na+ and K+ were the same in the roots, leaf sheaths and leaf blades between the tolerant and the sensitive lines. In order to study the molecular mechanism behind that, alleles of the HKT1;5 gene from five tolerant and five sensitive barley lines were cloned and sequenced. Sequence analysis did not show the presence of any polymorphism that distinguishes between the tolerant and sensitive alleles. Our real-time RT-PCR experiments, showed that the expression of HKT1;5 gene in roots of the tolerant line was significantly induced after challenging the plants with salt stress. In contrast, in leaf sheaths the expression was decreased after salt treatment. In sensitive lines, there was no difference in the expression of HKT1;5 gene in leaf sheath under control and saline conditions, while a slight increase in the expression was observed in roots after salt treatment. These results provide stronger evidence that HKT1;5 gene in barley play a key role in withdrawing Na+ from the xylem and therefore reducing its transport to leaves. Given all that, these data support the hypothesis that HKT1;5 gene is responsible for Na+ unloading to the xylem and controlling its distribution in the shoots, which provide new insight into the understanding of this QTL for salinity tolerance in barley.

Salinity tolerance of wild barley Hordeum vulgare ssp. spontaneum

“…n 43, n 23 and n 27) accumulated much lower Na in the leaves and roots, as compared to those of salinity‐sensitive genotypes (cultivars and a few wild barley genotypes). These findings were consistent with the previous studies on the wild grasses in which the critical role of the sodium (Na) ion in salinity tolerance has been highlighted, particularly at high levels of salinity stress (Arabbeigi et al, ; Hazzouri et al, ; Kiani, Arzani, & Habibi, ; Rezaei et al, ). The effects of the salinity stress on the leaf and root ionic contents also showed that the K concentration and K/Na ratio were significantly decreased under salinity conditions (Table ).…”

“…The ability to discriminate between Na and K in the soil solution and to preferentially exclude Na and accumulate K in the plant tissues has been recognized as the important contributors to salinity tolerance in the tribe Triticeae (Dvorak, Noaman, Goyai, & Gorham, ; Hazzouri et al, ; Shabala, Hariadia, & Jacobsen, ; Zhu, Shabala, Shabala, Fan, & Zhou, ). Hazzouri et al () demonstrated that HKT1;5 gene plays a key role in withdrawing Na from the xylem and therefore reducing its transport to the leaves in barley.…”

A cross population between D. kaki and D. virginiana shows high variability for saline tolerance and improved salt stress tolerance

“…However, the root expression was higher in roots of tolerant plants compared to sensitive which may explain its involvement in tolerance. As HKT1-driven tolerance is linked to the tissue-specific expression in other species [90][91][92], leaf and shoot expression would be necessary for explaining the phenotype of the studied populations. Regarding to the Clexclusion, both in DV and BC t tolerant populations, lower content in Clcan be associated with the lower relative values of g s and E compared to the control populations.…”

A Grain of Salt

“…The significantly associated region spanned approximately 6.6Mb, from 638,211,825 nt to 644,818,273 nt on the barley 4H physical map 21 and contained 247 gene models ( Supplementary Table 2 ). Common SNPs between the 50k and 9K iSelect platforms 22 aligned this association with a region recently shown to contain HvHKT1;5 20, 23 , and in the barley genome sequence HORVU4Hr1G087960, 140kb from the top scoring SNP (chr4H_638774955), was annotated as a homolog of OsHKT1;5. Considering this and previous functional studies 24–27 we conclude that HORVU4Hr1G087960 is the Na + specific transporter HvHKT1;5 .…”