Genetic Diversity Of HvGS5 Associated With Barley Grain Width

Barley is not only the main raw materials of beer industry and livestock of China,but also major food crop of Tibetan’s.Although China’s beer production has ranked first in the world for 12 years,the per capita consumption is much lower than the average level of developed countries.There will be a huge gap between at present China’s malting barley production and future consumption demand.Besides,the average yield of naked barley is less than 300 kg/mu in Qinghai-Tibetan highland.The yield level can be improved greatly compared with other crops.Thus,stabilizing and improving barley production is important for the sustainable development of barley industry. To discover the elite genes/alleles hidden in the barley collection and carry out barley breeding with molecular assistant selection,is an important way to select high yield barley varieties and meet the demand for growing beer consumption as well as the maintenance of national unity and regional stability.A total number of 186 naked barley with obvious changes of grain width(GW)and thousands kernal weight(TKW) were filtered out from primary core samples.Genome wide association study(GWAS) was performed with 40 pairs of EST-SSR molecular markers in this study.There were 12 markers highly correlated with GW and TKW traits.Among which,marker GBM1451 in barley chromosome1 H had the highest contribution rate. The corresponding candidate gene is homologous gene of rice OsGS5,which was named as HvGS5 in our study.Through the allelic variation analysis and association study,eight of 32 variation in this gene were determined as the related loci which were significantly associated with GW and TKW traits.Among which,the tandem repeats(TCG) number variation of InDel-8(in the 2nd exon) and the T/A base variation in SNP-6(in promoter region) were extremely significant correlated with GW and TKW traits.The contribution rate of InDel-8 for GW and TGW reached 10.61% and 11.16% respectively,and SNP-6 for GW reached 7.5%.Eight haplotypes of HvGS5 gene were obtained by gene polymorphism analysis.GW and TKW showed a gradually decreasing trend from H1 to H8 except H4 and H5.The number of repeated segment(TCG) s in the InDel-8 was negatively correlated with GW and TGW.It was speculated that the increasing of serine numberin HvGS5 enhanced the enzyme activity,which led to the GW reducing and TKW decreasing.In addition,the expression level of different haplotypes of HvGS5 genes of seed and glume increased from H1 to H8 during grain development stage.Except the expression of haplotype H4 decreased compared to H5.The transcription level of HvGS5 was significantly negative correlated with barley GW. The higher transcription level of HvGS5 corresponding to the narrower GW and the less TKW.Promoter analysis showed that SNP-6(T/A substitution) in the promoter region of HvGS5 caused a lack of transcription initiation component(TATA-box).It was suggesting that SNP-6 is another candidate key variation which affects barley GW and TKW by changing the gene transcription.