| High molecular weight glutenin subunits (HMW-GSs) are the critical components of wheat seed storage proteins. Variation in the composition and amount of HMW-GS are closely related to the nutritional and processing quality of wheat flour. Wild emmer wheat (Triticum dicoccoides, AABB,2n= 4x= 28) is the most primitive species with B genome in Triticum genus, in which there are extensive allelic variation of HMW-GS, especially those encoded by Glu-B1 loci. And,1By subunit, which is usually silent in common wheat, is also rich in wild emmer wheat. In order to understand the characteristics and efficiently utilize the 1By gene, one active 1By gene from T. dicoccoides accession D97 was cloned and characterized, in the present study. Sequence characteristics and phylogenetic relationship on this gene were analyzed, and the secondary structure of its encoded protein was predicted to evaluate its potential effect on wheat flour quality. The main results are as follows:1. An active 1By gene, 1By8.1 (GenBank No. KC545957), was successfully isolated from T. dicoccoides accession D97 with the four HMW-GSs. The open reading frame (ORF) of 1By8.1 was 2166 bp in size, most similar to the previous reported 1By8 with a high sequence identity at 99%. The polypeptide encoded by 1By8.1 contained 720 amino acid residues (aa) was with the typical structural characteristics of the HMW-GS of 1By type which consisted of the four domains including signal peptide of 21 aa, the conservative N-terminal domain of 104 aa with five cysteine residues (Cys), the central repetitive region of 553 aa with one Cys at position-73, and the conservative C-terminal domain of 42 aa with one Cys. Its central repetitive region contained abundant kinds of polypeptide, including tripeptide, pentapeptide, hexapeptide, nonapeptide, undecapeptide and dodecapeptide. Of which, hexapeptide was the most, reaching up to 67.9%.2. There were 19 single nucleotide polymorphisms (SNPs), including 12 transitions and 7 transversions between 1By8.1 (KC545957) and the three most similar 1By alleles 1By8 (JN255519, JF736014 and DQ537336) to it, resulting in the 12 aa substitution. So, 1By8.1 is a novel allele variation of Glu-B1-2.3. The nucleotide sequence of 1By8.1 is highly similar to that of the superior subunit gene 1By8 from common wheat. Its encoding protein 1By 8.1 possessed the similar primary and secondary structures to the superior subunit 1By8. In addition, its central repetitive region contained more α-helixes and β-sheets. Therefore,1By8.1 of T. dicoccoides accession D97 might be similar to, even more superior than the 1By8 in terms of the processing quality.4. Phylogenetic analysis showed that 1By8.1 and the other two 1By alleles (1By 16.1 and 1By16*) from T. dicoccoides were clustered into the three different subcludes, and separated from the 1By8 alleles from hexaploid common wheat and tetraploid poulard and durum wheats. The comparative analysis suggested that the Glu-B1-2 loci in T. dicoccoides existed abundant genetic diversity. However, in the processes of domestication into tetraploid cultivars and evolution into common wheat, the genetic diversity in Glu-B1-2 loci was decreased due to their molecular structural becoming progressively more close each other. Therefore, the abundant allele variation in Glu-Bl-2 loci from T. dicoccoides would be considerablely important genetic resources for modern wheat quality improvement. |
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