| To study the contribution of low molecular weight glutenin subunits (LMW-GS) to wheat (Triticum aestivum L.) quality and thevariation rule of LMW-GS in the somatic hybridization, LMW-GSs in hybrid lines 7-4-1-2, â…¡-6-1, â…¡-11-3 and their parents, Agropyron elongatum, and Triticum aestivum (wheat c.v. Jinan 177), were analyzed. The hybrid lines contain LMW-GSs identity to or different from both parents. Nine, eleven and eight LMW-GS genes were isolated and characterized by genomic PCR from Agropyron elongatum, parent wheat and their asymmetric somatic hybrid line 7-4-1-2, respectively. Comparison of the deduced amino acid sequences with those of published LMW-GS from common wheat and its related species shows that LMW-GSs from wheat c.v. Jinan 177 and their asymmetric somatic hybrid line 7-4-1-2 have higher identity to those of published LMW-GS, with a frequency over 80%; the average frequency is over 90%. Whereas, the LMW-GSs identity of A. elongatum to the published sequences is lower, with the variation rates from 50% to 90%; the average frequency is 72.3%. According to the first amino acid residue of the predicted mature protein, LMW-GS has been classified into three classes, type-s (serine), type-m (methionine) and type- i (isoleucine). Out of the 28 LMW-GS genes cloned in this paper, 20 are LMW-m type, including two of A. elongatum, seven of somatic hybrid and all of wheat. None belong to LMW-s type or i-type. Other 8 LMW-GS genes can't be classified into the three types because they are absent N-terminal regions. LMW-GS genes have been further classified into 6 types and 12 groups based on alignment of the conserved N- and C-terminal domains and sequence similarity of the deduced amino acid sequences (Ikeda et al. 2002). According this criterion, none of LMW-GS genes of the A. elongatum could be classified into those types and groups, but four and five LMW-GS genes of somatic hybrid and wheat cv. Jinan 177 could be classified into those types and groups, respectively. Pseudogene was frequently found in LMW-GS gene family. In this paper, 2, 1 and 5 LMW-GS genes were also characterized as pseudogenes from A. elongatum, parent wheatand their somatic hybrid line 7-4-1-2, respectively.The number and location of Cys residue, as well as the numbers of repetitive sequencerepeat are strongly correlated to flour quality. In the deduced sequences of LMW-GS genes acquired in this paper, most of them have 8 Cys residues. Five of somatic hybrid LMW-GSs has eight Cys residues, but subunits 8217 and 8129 have ten and seven Cys residues, respectively. Only one subunit of Jinan 177 has seven Cys residues, the others have eight Cys residues. The numbers of Cys residues of the subunits from A. elongatum changes widely. AeL 2 and AeL5 have9 Cys residues, AeL7 and AeL9 have 7 Cys residues, the rest 4 have 8 Cys residues. The position of Cys residue is relation with intra-and inter-molecular disulfide bonds, which result in the formation of the "glutenin polymer" and then influence flour technological characteristics. AeL2 and AeL5 from the A. elongatum contain 9 Cys residues and subunit 8217 from somatic hybrid line has 10 Cys residues. So, AeL2 and AeL5 can form three extra inter-molecular disulfide bonds and 8217 can form 4 extra inter-molecular disulfide bonds. Besides the Cys residues, a long N-terminal repetitive domain was also speculated to have positive influence on quality of wheat flour. In all deduced sequences, 9 have more repetitive units (about 20), including AeL2, and 8217, both are high homologous (99.4%) in the gene sequences. So we suggest that 8274 is originated from AeL2 and has positive effects on high quality of the hybrid line.Alignment analysis of all those genes in this paper revealed that four of hybrid line were clustered to those of Jinanl77, two were clustered to those of A. elongatum, rest two were not clustered to anyone from both parents. One LMW-GS gene was located on the ID chromosome by AS-PCR. |
PDF Full Text Request