| Soil salinization is one of the most serious abiotic stresses, which poses a great threat to crop production and food security in the world. Thus, the transformation and utilization of saline-alkali lands have become an important issue in the sustainable agriculture. Development of salinity-tolerant crop cultivars through genetic improvement is regarded as an efficient and fundamental strategy for increasing crop productivity in saline environment. The elite germplasm and understanding of the mechanism in salt tolerance is crucial for developing the cultivars with salinity tolerance. In order to exploit elite alleles associated with salinity tolerance, the present studies were conducted with focusing on the unique and precious germplasm in China, the Tibetan annual wild barley(H. vulgare subsp.spontaneum) to illustrate the physiological and genetic characteristics o f salinity tolerance. The main results are as follows:1. There was a wide variation among wild barley accessions in salt tolerance. The salinity tolerance of 189 Tibetan wild barleys was evaluated in terms of relative shoot dry biomass under salinity stress and it was found that the examined germplasm exposed to the stress of 300mM NaCl showed a wide range of genetic variation. Compared with well known salt-tolerant cultivar CM72,139 genotypes showed a stronger salt tolerance, suggesting that Tibetan wild barley may offer elite alleles for salt tolerance improvement of barley. Furthermore, the physiological mechanism of salt tolerance was analyzed and it was found that salt tolerance is negatively correlated with Na+ content and the ratio of Na+/K+ in shoot (r=-0.455, p= 0.0012; r =-0.495, p= 0.0004), and while positively correlated with K+ content in shoots (r= 0.296, p= 0.04), indicating that salt tolerance in Tibetan wild barley is mainly attributed to regulation of ion homeostasis2. Six QTLs associated with salinity tolerance were indentified. The QTL analysis of 25 traits associated with salinity tolerance was carried out using a DH population derived from a cross Yerong and Franklin). Briefly, we detected six QTLs, located on the chromosome 2,6 and 7, respectively. The QTLs, controlling the relatively-reduced K+content in shoot, as well as the ratio of Na+/K+ in root under salt stress were located on the position of 125 and 150cM in chromosome 2, respectively. The QTL, controlling shoot dry biomass under salinity was detected on the locus 79cM in chromosome 6. The QTLs, located on the position of 58 and 72 cM in chromosome 7, controlled root and plant dry biomass and Na+ content in root under non-saline environment, respectively, and could explained 10-18% of the phenotypic variation. Moreover, comparative genomics analysis showed that the candidate genes close to the QTLs located on 2H and 7H might be HKT-like gene.3. Tibetan wild barley showed a wide genetic diversity. The population structure and linkage disequilibrium were analyzed for the Tibetan wild barley using 1125 DArT markers covering the whole genome, and it was found that this natural population can be divided into eight subgroups, indicating its wide genetic diversity. The distance of the whole genome LD extension was up to 20cM, of which LD on the chromosome 2,6 and 7 decreased rapidly and extended to 12.5,10 and 15cM, indicating that the population is suitable for genome-wide association mapping. Furthermore, the whole genome association analysis detected thirty DArT markers distributed over the whole chromosomes, which accossiated with relative shoot biomass under 300mM NaCl condition significantly. Among them, the markers located on 149.4cM and 58 cM of chromosome 2 and 7, respectively, were consistent with the QTLs detected in a DH population (Yerong/Franklin) controlling salinity tolerance, confirming the accuracy of QTL mapping. It may be suggested that joint linkage mapping and association mapping is a powerful tool for studying the quantitative traits in crop.4. The structure and allelic function of HvHKT1 and HvHKT2 were analyzed. HKT was assumed as a candidate gene for salinity tolerance. The structure, expression patterns, allelic and functional diversity of HvHKT1 and HvHKT2 were analyzed. The whole length of 2,505 and 2,055 bp genomic DNA sequences for HvHKT1 and HvHKT2 were cloned, respectively, and HvHKT1 was firstly reported (GenBank accession number JF496205). Both of these two genes were trans-membrane proteins, and the serine (S129) and glycine (G91) in the first loop determined the selectivity to Na+ and K+. Furthermore, the expression pattern of HvHKT1 and HvHKT2 were analyzed using real time PCR and found that HvHKT1 was induced by salinity, while HvHKT2 was down-regulated by salt stress. Moreover, based on association analysis of candidate gene, we found that HvHKT1 mainly control Na+ absorption, and HvHKT2 involved in K+ transport under salinity, suggesting that these two genes play an important role in Na+ and K+ homeostasis. In addition, HvHKT1 was located at DArT marker bPb-8737(108.7cM) on barley chromosome 2, which consistent with the conclusions gained in the previous genetic analysis.
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