| Grain hardness, or kernel texture, is one of the most important agronomic traits of wheat and directly determines milling quality of wheat. Grain hardness, as well as seed storage proteins in wheat endosperm, jointly determines wheat quality. Two major genes controlling grain hardness, Puroindoline a(Pina) and Puroindoline b(Pinb), are located at the Hardness(Ha) locus on the short arm of chromosome5D of wheat, encode two proteins of ca.14kDa, PINA and PINB. In common wheat(Triticum aestivum L.), the soft-texture phenotype of grain requires the wild-type of both Pin genes (the Pina-D1a and Pinb-D1a alleles), while non-expression or mutations in either of the Pina or Pinb gene is associated with hard texture. Most varieties of tetraploid durum wheat(Triticum turgidum L. ssp. durum) have harder grain textures than common wheat varieties due to lack of the D genome and consequentially the Pina and Pinb genes.Pina and Pinb genes determine grain hardness in some type of synergism, while grain hardness also influences plenty of food-processing qualities; however, only a few studies have focused on the effects of Pin genes on food-processing qualities of wheat. In order to investigate the effects of PINA on food-processing qualities, we screened out transgenic lines of durum wheat homozygous for the foreign Pina gene. Analyses on the PINA protein levels, grain hardness and dough mixing properties of these transgenic and control lines demonstrated that expression of PINA not only decreased grain hardness, but also had detrimental effects of dough mixing properties, with significantly decreased dough resistance to extension observed in transgenic lines. It is demonstrated that food-processing qualities of wheat are largely controlled by seed storage proteins, especially by high-molecular-weight glutenin subunits (HMW-GS). We therefore raised the question of whether this detrimental effect of PINA on food-processing qualities would be consistent under genotypes with different compositions of HMW-GS. To clarify this question, a cross between two transgenic lines of durum wheat expressing1Ax1and Pina was made, which have the same genetic background. Lines coexpressing1Ax1and Pina, lines exclusively expressing1Ax1or Pina and lines containing neither1Ax1nor Pina were selected from the crossing progenies. Results of grain hardness and dough mixing properties from these lines showed that dough properties of lines coexpressing1Ax1and Pina were superior to the others, with no negative effects of PINA on the food-processing qualities being detected in "1Ax1-Pina" coexpressing lines. These results indicate that both proteins of PIN and HMW-GS have influences on food-processing qualities of wheat, and that transgenically expression of Pina and1Ax1shows combined effects on food-processing qualities.To further investigate the effects of two proteins of PIN and HMW-GS on food-processing qualities of common wheat, the pPA-RNAi and pPB-RNAi vectors, used for inducing the RNA-mediated silencing of the Pina and Pinb genes, were separately or combinationally introduced into a soft-textured common wheat variety L88-31. A total of six To transgenic plants were recovered from the three different plasmid conbinations and confirmed by PCR. Of these, three were produced under PPT selection following bombardment with the plasmid pPA-RNAi, one with pPB-RNAi and two with both plasmids. These transgenic lines will be valuble in studying the effects of Pina and/or Pinb genes on food-processing qualities in common wheat and in carrying on comparative analyses of food-processing qualities between durum wheat and common wheat.In brief, the results in the present study suggest that both wheat storage proteins and PIN proteins should be targets of genetic improvement of wheat quality, and possible combined effects of PINs and major groups of storage proteins on wheat qualities should be taken into consideration. |
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