| High molecular weight (HMW) glutenin subunits are one group of the major components of storage proteins in wheat seeds, variation in the amount and composition of HMW glutenin subunit would affect and determine the flour processing quality. Analysis of the composition of the HMW subunits of glutenin has proved to be a useful tool not only for plant breeding, mainly due to its important association with bread-making quality which has aroused the interest in the identification of novel types of HMW subunits that can be exploited in wheat quality improvement programmes, but also for assessment of genetic diversity in wheat germplasm resources. In present study, we analyzed the composition of the HMW glutenin subunits in landraces, improved and newly bred cultivars/lines of common wheat (Triticum aestivum L.) from Hubei province, China, together with Chinese endemic wheats (Tibetan weedrace, Yunnan hulled and Xinjiang rice wheat) and Aegilop tauschii Coss., furthermore, the genetic diversity at Glu-1 loci among these materials was also evaluated. The main results are as follows.1. Identification of novel HMW glutenin subunit alleles in common wheatSix novel alleles of HMW glutenin subunits have been found among 391 accessions of common wheat from Hubei, (1Bx7*+1By8*), (1Bx6+1By8**) and (1Bx7+1By8**) were encoded by Glu-B1 locus, and (1Dx4+1Dy null), (1Dx4+1Dy9.5) and (1Dx5*+1Dy12) were at Glu-D1 locus.2. Composition of the HMW glutenin subunits at Glu-1 loci in common wheatThe alleles of 1Ax1, 7+8 and 2+12 were the most dominant at each of the Glu-1 loci among the landraces, improved and newly bred cultivars/lines, but allelic frequencies varied among the three different populations.By comparing the allelic frequencies in newly bred cultivars/lines with that of improved cultivars/lines and landraces, it was found that, at Glu-A1 locus, the frequency of 1Ax null in newly bred cultivars/lines decreased 12.77% and 23.85%, but the frequency of subunit 1Ax1 increased 9.61% and 20.31%. At Glu-B1 locus, the frequencies of subunits 14+15 and 7+9 in newly bred cultivars/lines increased, subunits 14+15 increased 4.53% and 7.7% while 7+9 increased 5.01% and 20.95%, respectively. However, the frequencies of 7+8 and 17+18 decreased in newly bred cultivars/lines, 7+8 decreased 4.93% and 23.13%, 17+18 decreased 1.1% and 4.95%. The frequency of subunits 2+12 decreased in newly bred cultivars/lines with the amount of 32.38% and 20.3%, whereas the frequency of subunits 5+10 increased with the amount of 32.6% and 20.86%.Generally, the composition of HMW glutenin subunits in newly bred cultivars/ lines has been improved comparing with improved cultivars/lines and landraces, the frequency of analyzed materials with 5+10 increased 17.35% and 32.01% but those containing subunits 2+12 decreased 33.62% and 14.36%, respectively.3. Genetic diversity and gene differentiation in landrace of common wheatThe genetic diversity indexes were relatively high in the collection of common wheat landrace analyzed, with values of A=5.33, P=1.00, Ae=1.352 and H=0.2381, but variations existed within the six subpopulation representing six different wheat cultivation regions. The indexes of the third wheat cultivation region (A=3.67, P=1.00, Ae=1.451, H=1.2787) were the highest among the six regions while the second region were the lowest one (A=1.33, P=0.33, Ae=1.123, H=0.0896).The mean gene diversity within populations (HS=0.1941) was greatly higher than that of the mean gene diversity among populations (DST=0.0439), indicating that greater gene diversity exists within the populations than between the populations.The average of the relative degree of gene differentiation among populations (GST) over all Glu-1 loci was 0.185, which means that 18.46% of the total gene diversity was between populations while 81.54% of the gene diversity was within the populations.4. Comparison of the genetic diversity among the populations of newly bred, improved cultivars/lines and landracesThe numbers of alleles detected in newly bred cultivars/lines were lower than that in improved cultivars/lines and landraces, with 16 alleles found in landraces, 15 and 14 in improved and newly bred cultivars/lines, indicating the variations of HMW glutenin subunits are abundant in landraces. However, the genetic diversity of newly bred cultivars/lines was 0.5340, higher than that of improved cultivars/lines (H=0.4169) and landraces (H=0.2442), suggesting the distribution of alleles in it was more balanced than that of the others.5. Genetic diversity of HMW glutenin subunits among Chinese endemic wheatsTen alleles at Glu-1 loci were detected among 50 accessions of Tibetan weedrace wheat (T. aestivum ssp. yunnanense King), and one novel allele (7**+8) and one rare allele (2+12*) were also found. Seven HMW glutenin subunit compositions resulted form different combinations of the ten alleles, (null, 7+8, 2+12) was the most common combination with the frequency of 69.64%. Analysis results indicate that the genetic diversity at Glu-1 loci in the collection of Tibetan weedrace wheat evaluated was relatively low with four indexes of A=3.33, P=1.00, Ae=1.220, H=0.1646.Four types of HMW glutenin subunit combinations were detected in 10 accessions of Yunnan hulled wheat (T. aestivum ssp. tibetanum Shao), they were (null, 7, 2+12), (null, 7+8, 2+12), (null, 17+18, 5+10) and (null, 7+8, 2+12*).Two accessions of Xinjiang rice wheat (T. petropavlovskyi Udacz et Migush) all possessed HMW glutenin subunit combinations of (null, 7+8, 2+12).6. HMW glutenin subunit compositions in Aegilops tauschiiFive x-type and four y-type glutenin subunits of high molecular weight were identified in 47 accessions of Aegilops tauschii. Subunit 1Dtx1.1 was one novel x-type glutenin subunit, with the slower mobility than subunit 1Ax1 in common wheat, and at present, it might be the subunit with the largest molecular mass reported in the species of Aegilops tauschii.Eight alleles were found in this collection, 1.1~t + 11~t,1~t + 11~t,1.5~t + 12~t,2~t + 10.1~t,2~t + 11~t,2~t + 12~t,2~t + 12.4~t,3~t + 11~t. Among them, two novel alleles, 1.1~t + 11~t and 2t + 12.4t, were reported in this study for the first time.Results obtained in the present studies should provide new materials and useful references for common wheat quality improvement and basic genetics research as well. |
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