Elucidating The Composition And Function Of Low-molecular-weight Glutenin Subunit Genes In Bread Wheat

Low-molecular-weight glutenin subunits are the major components of seed storage proteins in common wheat. They play an important role in determining the bread-making quality of bread wheat. However, LMW-GS display high polymorphic protein complexes and are encoded by a multi-gene family. Elucidating the complex gene family in bread wheat remains challenging, which has limited the function analysis of LMW-GS and hindered their utilization in wheat quality improvement. In the present study, we investigated the micro-core collections of Chinese wheat germplasm and a Near-Isogenic Line population of LMW-GS using the LMW-GS gene marker system, the full-length gene cloning method and two-dimensional electrophoresis. The composition, sequence characteristics, expression analysis and function difference of LMW-GS in Chinese wheat germplasm were studied and discussed.In the micro-core collections of Chinese wheat germplasm, at least15LMW-GS genes were identified from a wheat variety. Their deduced proteins belonged to the typical LMW-GS and possessed eight conserved cysteine residues. At the Glu-A3locus, two m-type genes and2-4i-type genes were identified from individual wheat varieties, and1-3genes were generally expressed in developing seeds. At the Glu-B3locus,2-3m-type genes and1-3s-type genes were detected, and2-4of them were active. LMW-GS genes at the Glu-D3locus are conserved, and eight genes were identified from each variety, of which six encoded LMW-GS. LMW-GS genes at Glu-A3and Glu-B3loci showed high genetic diversity among wheat varieties, and the number of active genes were greatly different among genotypes. All i-type genes were located at the Glu-A3locus. They were tightly linked and formed12kinds of haplotypes in Chinese wheat germplasm. The s-type genes at the Glu-B3locus were also co-segregated and formed two groups of haplotypes. Sequence clustering analysis showed that i-type and s-type genes were classified into individual groups, and m-type genes at Glu-3loci were divided into four groups. In addition, based on the data from the core-collections of Chinese wheat germplasm, we developed an updated LMW-GS gene marker system to easily and accurately elucidate the complex gene family in bread wheat.To study the effects of LMW-GS on wheat quality properties, we investigated the Aroona near-isogenic lines containing five Glu-A3alleles, eight Glu-B3alleles and five Glu-D3alleles。Using the LMW-GS gene marker system and two-dimensional electrophoresis, we analyze the encoding genes and whole proteins for each allele. The results showed that the composition and nucleotide sequences of LMW-GS genes were significantly different among LMW-GS alleles, while the electrophoretic patterns of gliadins were similar for most alleles. For five Glu-A3alleles, Glu-A3e was an inferior allele on all quality properties. For eight Glu-B3alleles, Glu-B3g and B3b were correlated with superior bread-making quality, while Glu-B3c and B3d alleles produced the smallest quality properties. And For five Glu-D3alleles, there is no significant difference in all quality parameters measured in the present study. Moreover, all the alleles with superior dough resistance and pan bread quality also possessed high content of SDS-unextractable glutenin polymeric protein. Thus, the unique LMW-GS genes in individual alleles determined dough viscoelasticity by modifying the size distribution of glutenin polymers and the aggregative properties of glutenins.