| Wheat gluten is divided into gliadin and glutenin, and glutenin is divided into high-molecular-weight glutenin and low-molecular-weight glutenin. Even though high molecular weight glutenin subunits (HMW-GS) only accounts for 12% of the wheat storage protein, they act as "network backbone" in the gluten, greatly affect the structure and property of gluten, which play an important role in determinating the processing quality in common wheat. Therefore, reliable effect evaluation of allelic variation at Glu-1 on the processing quality is very essential for making breeding plan. In this study, ten HMW-GS near isogenic lines in genetic background of Yanzhan No 1 were used for evaluating the effect of different HMW-GS compositions on the bread-making quality and noodles quality. In addition, mechanism for 1Dx5 silencing in natural mutant plant was studied preliminarily.1. Ten near isogenic lines of Yanzhan No 1 were bred. Seeds were collected from Beijing and Luoyang respectively in two growing seasons, 2007, 2008). Though there is differenence on the processing quality characteristics between Beijing and Luoyang, the trends are consistent.2. HMW-GS compositions have great effection on bread score, and the variation coefficient between near isogenic lines with different HMW-GS compositions is 21.45%. Bread volume was significantly correlated positively with dough development time (r = 0.90, P < 0.01), Zeleny sedimentation (r = 0.89, P < 0.01), dough stability time (r = 0.67, P < 0.05) and flour protein content (r = 0.52, P < 0.05). Therefore, bread score was significantly and positively correlated with bread volume (r = 0.98, P < 0.01), Zeleny sedimentation (r = 0.93, P < 0.01), and dough development time (r = 0.89, P < 0.01). 3. BMQ tests indicated that the expression of 1Ax1 at Glu-A1 locus could improve BMQ in most lines. Contribution of alleles at Glu-B1 to BMQ was 7+8>14+15>6+8>7 in lines with Null subunit at Glu-A1 and 5'+12 at Glu-D1. However, it was 6+8>14+15>7 in the lines with 1 at Glu-A1 and 5'+12 at Glu-D1. When Null subunit was at Glu-A1, lines with 14+15 and 5+10 subunites were slightly better than those with 14+15 and 5'+12; In addition, lines with 7+8 and 5'+12 were much better than those with 7+8 and 5+10. Compared to the 5+10 lines, silence of 1Dx5 caused significant BMQ decline. Therefore, it seems that there is complementary effect between X-type and Y-type of HMW-GS on BMQ and either absence will cause decline of BMQ.4. Effection of HMW subunit compositions on noodles processing quality (NPQ) was also examinated. The results of correlation analysis showed that the composition of HMW-GS had great impact on the property of rheology; Kernel protein content is significantly correlated negatively with dough stability time (r = -0.67, P < 0.01), dough energy (r = -0.63, P < 0.01), Max.resistance (r = -0.63, P < 0.01); the farinograph parameters are significantly correlated positively with extensograph parameters to different extents. Kernel protein content are significantly correlated negatively with noodles color (r = -0.86, P < 0.01), stickness (r = -0.61, P < 0.05), firmness (r = -0.70, P < 0.01) and total score (r = -0.77, P < 0.01), noodles color is significantly correlated positively with dough stability time (r = 0.56, P < 0.01), dough energy (r = 0.54, P < 0.05) and Max.resistance (r = 0.51, P < 0.05).5. The results of noodles processing quality tests indicated that the expression of 1Ax1 at Glu-A1 locus couldn't always improve NPQ. Contribution of alleles at Glu-B1 to NPQ was 7>14+15>7+8>6+8 in lines with Null at Glu-A1 and 5'+12 at Glu-D1. However, it is 6+8>14+15>7 in the lines with 1 at Glu-A1 and 5'+12 at Glu-D1. When Null was at Glu-A1, 14+15 or 7+8 at Glu-B1, 5+10 subunites were better than 5'+12. In addition, 14+15 are high quality subunits for NPQ, the silence of 1Dx5 causes significant NPQ decline, but the deficiency of 1By8 made NPQ of 7, 5'+12 enhance significantly. Therefore, it seems that there is complementary effect between X-type and Y-type of HMW-GS on NPQ.6. The silent mechanism of 1Dx5 gene was studied. No transcription products were detected by RT-PCR, while the 1Dx5 gene can be amplifiyed by PCR genomic DNA of the mutant. Therefore, we conclude the 1Dx5 gene silence occurs during transcription. The degree of methylation of 1Dx5's promoter was examed by bisulfite sequencing. The results showed that methylation is very serious in 1Dx5 peomoter H1 district (-1972--1394) either mutant (95.5%) or wild type (93.25%), but there is no significant diference between them. Degree of methylation in the promoter H2 district (-450bp-+323bp) of the mutant is much more than that in wild type. The methylation proportion is 88.7% and 50.3% respectively and there exixted statistical significant difference (P < 0.01). Hense, we estimate that the 1Dx5 gene transcriptional silencing is caused by methylation in 1Dx5's promoter. |
