The Evolutionary Relationship And Divergence Mechanism Of Selected Metabolites From Barley Of Different Origins

Wild barley(Hordeum vulgare ssp.spontaneum)is the ancestor of cultivated barley(Hordeum vulgares ssp.vulgare).Because of its rich genetic diversity and sterile isolation from cultivated barley,wild barley is considered to be the primary gene bank for character improvement of cultivated barley.The domestication and dissemination are the two hot issues in academic circles of barley,but they are still controversial today.In this study,9 near East wild barley(Wb-NE),10 Tibetan wild barley(Wb-T)and 10Chinese cultivated barley(Cb-C)were analyzed by transcriptome and metabolism for identifying the origin of Chinese barley and the molecular mechanism of metabolite differentiation in the process of evolution.The main results are as follows:1.Through transcriptome sequencing and quality control,a total of 29 germplasms were obtained 185.60Gb Clean reads.Through mutation detection,a total of 1,182,394SNPs were obtained from 29 germplasms,and then 176,741 high quality SNPs were obtained after filtration.The genetic diversity of three barley populations was evaluated based on the SNPs set.The results showed that the genetic diversity of Wb-NE was the highest(π=0.23036,θ_W=0.21255,MAF=0.1745 and PIC=0.2176),followed by Wb-T,and the lowest is Cb-C.The results of PCA,population structure analysis and phylogenetic tree showed that the genetic differentiation was obvious between cultivated barley and wild barley.At the same time,Wb-NE was located at the base of the rooted evolutionary tree and differentiated first from bulbous barley(at the first node),then Wb-T differentiated from Wb-NE(at the second node),and finally,Cb-C differentiated from Wb-T(at the third node).These results suggest that the evolution of Cb-C may be from Wb-NE to Wb-T and finally to Cb-C,the hybrid phenomenon of some germplasm indicates that there is a phenomenon of gene flow in the process of evolution.identical by descent.2.Through the identical by descent(IBD)and ABBA-BABA statistical analysis by three populations,he results showed that 30 and 16 pairs of germplasm shared the same haplotype in Wb-T and Cb-C respectively,while only 3 pairs were detected in Wb-NE.HS26 and HS56 germplasm did not share the same haplotype with other germplasm in Wb-NE,which represented the most primitive genomic state and supported the theory of near-eastern origin of barley.In addition,three tree topology models are obtained from the statistical results of ABBA-BABA.Among them,the(((T,C),E),HS18)model is the best tree topology,and the D statistic of this model is 0.1679(>0),Z score is 6.021(>3),indicating the infiltration between Wb-NE and Cb-C.The other two models showed that gene infiltration also existed in Wb-T and Cb-C.3.The genomic similarity analysis of 25 barley germplasms from three populations based on 114120 SNPs showed that the similar genomic windows between Cb-C and Wb-T group,Cb-C and Wb-NE group were 560,281 respectively,while those between Wb-T and Wb-NE were the most groups(659).In addition,by observing the distribution of similarity windows on chromosomes,it was found that compared with Cb-C and Wb-NE group,Cb-C and Wb-T group had significantly more similarity windows on 7chromosomes,especially in 1H,4H and 7H staining,it is as high as 2 to 3 times.The averageπratio of Wb-NE to Wb-T group was 1.0455 and the average ROD value was-0.0455,while that of Wb-T and Cb-C group was 0.8708 and 0.1292 respectively.The above results showed that the genetic similarity between Wb-NE and Wb-T was the highest and the genetic differentiation was the lowest.In addition,compared with Wb-NE,Wb-T had the higher genomic contribution to Cb-C.The selected genes of the two evolutionary processes were screened and annotated by KEGG analysis with the Fst>0.5,a total of 261 selected genes were annotated from Wb-NE and Wb-T groups,and 1390 selected genes were annotated from Wb-T and Cb-C groups.4.Combined with metabolic group analysis,a total of 8828 non-redundant metabolites were detected in three population,including 328 annotated metabolites.PCA and cluster analysis of all metabolites showed that the metabolite differentiation occurred in the two evolutionary processes from Wb-NE to Wb-T and from Wb-T to Cb-C.1850metabolites(55 annotated)and 2766 metabolites(108 annotated)were strongly selected during the evolution from Wb-NE to Wb-T and from Wb-T to Cb-C,respectively.And all the annotated selected metabolites showed three evolutionary characteristics in the two evolutionary processes.The first is the metabolites of alkaloids(N-Methyltyramine and Hordenine)selected only in the process of transmission from Wb-NE to Wb-T,the second is the metabolites selected in both evolutionary processes,and the third is the metabolites of phenylpropanes(L-Phenylalanine,4-Hydroxycinnamicacid and Apiin)selected only in the domestication process from Wb-T to Cb-C.5.Combined with the selected genes,the genetic mechanisms of two metabolites that showed specific differentiation in the process of evolution were studied respectively.the results showed that five selected genes were involved in the synthesis of N-methyltyramine and hordenine in the evolution from Wb-NE to Wb-T,among which 8synonymous mutations and 5 missense mutations were found in the coding region of HORVU6Hr1G027650.These five missense mutation sites may be the key mutation sites leading to the differentiation of alkaloid metabolites in this evolutionary process.During the evolution from Wb-T to Cb-C,five selected genes were closely related to phenylalanine,p-coumaricacid and apiin,among which two synonymous mutations and four missense mutations were found in the coding region of the gene HORVU4Hr1G072150.These four missense mutations may be the key mutation sites leading to the differentiation of phenylpropane metabolites in the process of evolution in barley.