| High molecular weight gluten subunits(HMW-GSs)play a critical role on wheat flour processing quality,even they just account for less than 2%of the total weight of wheat grains.HMW-GSs are encoded by the loci Glu-1,locating on the long arm of homoeologous chromosome group in wheat and its relatives.Of which,Glu-1D on chromosome 1D has the most important contribution for wheat quality.Subunits 5+10 and 2+12,representing the most popular types of Glu-1D loci in wheat varieties,are well known for their relationship with bread quality.However,the effects and breeding values on Chinese traditional cooking food are not clear,especially in Sichuan province where sunshine is limited.On the other hand,common wheat has a low genetic diversity of HMW-GSs compared to its wild relative species,due to the genetic bottleneck created by polyploidization and artificial selection.Aegilops is the most closely related to wheat and has rich HMW-GS variations,thus valuable to break the genetic bottleneck.Based on previous reports,the locus Glu-1U on U-genome in Aegilops species probably harbors beneficial HMW-GS variations for wheat quality improvement.In the present study,we analyzed the correlations between HMW-GS compositions and quality traits of wheat varieties released in Sichuan since 1949,investigated the quality effects of 5+10 and 2+12 subunits,and introgressed the HMW-GSs encoded by Glu-1Uk from Aegilops kotschyi into Sichuan wheat.The main results are as follows:Based on the analysis of HMW-GS compositions in 184 Sichuan wheat varieties released from 1949 to 2018,there were three alleles at Glu-1A including 1,N,2*,eight at Glu-1B including 7,20,22,7+8,7+9,6+8,14+15 and 23+18,and three at Glu-1D including 5+10,2+12 and 3.1t+11*t.With the breeding process,the diversity of alleles increased,and the ratio of high-quality strong gluten 1 and 5+10 increased gradually.In terms of individual loci,5+10 had a positive effect on the stability time,while alleles of Glu-1A and Glu-1B affected on unit weight,protein and wet gluten contents.The 14 subunits formed 24 combinations,with the N/7+9/5+10 having the highest frequency(12%).N/6+8/2+12,N/6+8/5+10,1/20/2+12 and 1/20/5+10 were related with weak gluten and the 1/7+8/5+10,1/7+9/5+10 and N/7+8/5+10 related with medium gluten.The near-isogenic lines were developed to accurately evaluate the effects of 5+10 and 2+12 encoded by Glu-1D locus,and the background subunits of the Glu-1A and Glu-1B sites were 1 and 20,respectively.A heterozygous plant,showing 5+10 and 2+12 at Glu-1D locus,was selected from wheat line Shumai 1764 by screening the residual heterozygous line(RHL).The sister lines Shumai 1764A and Shumai 1764B which expressed 5+10 and 2+12 subunit were selected,respectively.According to single nucleotide polymorphism(SNP)analysis,their major differences o were found in the 403-414 MB region of chromosome 1D which contains the Glu-1D locus,confirming Shumai 1764A and B were near-isogenic lines,which were excellent materials for comparative study of quality.Based on the results from the multi-point test and the regional test in Sichuan province,there was no significant difference in the observed agronomic traits.This excluded the interference of varied agronomic traits on quality test,allowing an accurate evaluation on quality.Based on the data from six environments in the regional test of Sichuan province,the near-isogenic lines Shumai 1764A and Shumai 1764B were excellent with a higher yielding of 2.2%and 1.9%than the commercial check Mianmai 367.It indicated that the yielding level of near-isogenic lines Shumai 1764A and B were close to that of the major commercial variety and the differences of the Glu-1D region have no significant effects on yield.The seeds used for the quality test were collected from the multi-point test and the regional test in Sichuan province to reflect the overall environment conditions of Sichuan province.Out of the quality parameters,grain protein content was similar between 5+10 and 2+12 but the 5+10 increased gluten strength and decreased elongation.From the end use quality,5+10 subunit was better than 2+12 for bread and steamed bread.However,for noodle,2+12 was better than 5+10.Meanwhile,they exhibited similar quality of dumplings and biscuits.In quality improvement,therefore,5+10 should be a prior for bread and steamed bread,while 2+12 should be used for noodle wheat breeding.To exploit the HMW-GS variations in the relate species Ae.kotschyi(UkUkSkSk,2n=2x=28),the disomic 1Uk(1A)substitution line N124 was developed.N124 was derived from the successive selfing of the hybrids between common wheat line Y10-176 as female and Ae.kotschyi accession AS 19 as male parent.Fluorescence in situ hybridization karyotypes showed that N124 was a disomic 1Uk(1A)substitution line.SDS-PAGE and reversed phase high performance liquid chromatography(RP-HPLC)verified that N124 expressed two HMW-GSs from 1Uk.PacBio RNA sequencing and phylogenetic analysis confirmed that the two HMW-GSs were Ukx and Uky.Sequence comparison indicated that Ukx from the substitution line N124 had a high homology with previously reported genes at Glu-1U locus.However,the size of the repetitive domain of Uky in N124(738 residues)was much larger than that of a previously reported Uy subunit(GeneBank:AAL82616,655 residues).The large repetitive domain of Uky in N124 was due to the insertions of tandem repeats of standard nonapeptides(GHYFASLQQ)and irregular tripeptides and hexapeptides.Larger repetition regions usually contain more hydrogen bonds and β-turn structures formed by glutamine residues,which are conducive to the formation and stability of glutenin macropolymer and resulting in better molecular elasticity of proteins.To further evaluate the breeding value of the substitution line N124 in quality improvement,the agronomical traits and quality parameters were analyzed using the samples collected from six experimental environments.The integrated agronomic traits of N124 were slightly worse than the common wheat parent Y10-176,mainly attributing to a significant reduction in the setting ratio.However,N124 improved several major quality parameters such as higher protein content,sedimentation value,wet gluten content,stability time and grain hardness.Therefore,N124 could be served as a donor or bridge material for wheat quality improvement. |
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