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

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.‎

Authors: 
Khaled M.‎ Hazzouri, Basel Khraiwesh, Khaled M.‎ A.‎ Amiri, Duke Pauli, Tom Blake, Mohammad Shahid, Sangeeta K.‎ Mullath, David Nelson, Alain L.‎ Mansour, Kourosh Salehi-Ashtiani, Michael Purugganan and Khaled Masmoudi
Year: 
۲۰۱۸
Publication type: 
Scientific Paper
Publication Source: 
Frontiers in Plant Science