Genetic Effects Of Genes Encoding Sucrose Synthase And ADP-Glucose Pyrophosphorylase In Grain Development And Gene Selections In Global Wheat Breeding

In China increases in wheat(Triticum aestivum L.) production are mainly due to increases in yield. Wheat yield mainly depends on three components, spike number per area, grain number per spike and thousand kernel weight(TKW). Starch accounts for about 65% to 80% of the grain endosperm, so starch synthesis could largely influence TKW. In the starch synthesis pathway of the grain, sucrose synthase(Sus) and ADP-glucose pyrophosphorylase(AGPase) are considered as key enzymes. In this study, haplotypes of Ta Sus and Ta AGP were researched by relevance analysis to target several favored haplotypes associating with high TKW. The frequency changes of favored haplotypes were studied over the last century of wheat breeding worldwide.1. In this study, six Sus genes were cloned, Ta Sus2-2A/2B/2D and TaSus1-7A/7B/7D. Two, two, five and two haplotypes were found at Ta Sus2-2A, Ta Sus2-2B, Ta Sus1-7A and Ta Sus1-7B. Molecular markers were developed to scan different populations. In Chinese modern cultivars, TKW of Ta Sus2-2A-Hap-A were significantly higher than-Hap-G in three years, and that of Ta Sus1-7B-Hap-T were significantly higher than-Hap-C. The frequencies of two favored haplotypes were increased by 40% over six decades of Chinese wheat breeding process. Ta Sus2-2B-Hap-H and Ta Sus1-7A-Hap-1/2 were considered as favred haplotypes detected in near-isogenic lines(NILs). The frequencies of these favored haplotypes were increased differently during the process from landraces to modern cultivars. In NILs, favored haplotypes of Ta Sus2-2A and Ta Sus1-7A had higher expreesion levels and enzyme activities than non-favored ones. The frequencies of Ta Sus1-7A-Hap-1/2 were over 95% in both landraces and modern cultivars, for two SNPs in the sixth exon of non-favored ones might decrease the ability of the enzyme binding to the substrate. Ta Sus1-7A might be selected in tetraploid wheat. Favored haplotypes of four genes had high frequencies in six wheat-breeding regions, suggested these haplotypes were selected worldwide.2. Nine AGP genes were cloned, Ta AGP-S1-7A/7B/7D, Ta AGP-S2-5A/5B/5D and Ta AGP-L-1A/1B/1D. Four and four haplotypes were found at Ta AGP-S1-7A and Ta AGP-L-1B. In NILs, Ta AGP-S1-7A-1/2 and Ta AGP-L-1B-Hap-1/2/3 were considered as favored haplotypes(-Hap-I) for they were associated with higher TKW. Similar results were tested in the mini-core collectons and modern cultivars. One SNP in the third exon of non-favored haplotypes of Ta AGP-S1-7A might decrease the ability of the enzyme binding to the substrate. The SNP at position-122 of non-favored haplotypes of Ta AGP-L-1B decreased the promoter-driven ability which validated in the transgenic rice lines. The frequencies of two favored haplotypes were increased by 50% over six decades of the wheat breeding process, and the combination of two favored ones was also artificially selected. Ta AGP-S1-7A might be selected in tetraploid wheat.3. The combination of six favored haplotypes(Ta Sus2-2A-Hap-A, TaSus2-2B-Hap-H, Ta Sus1-7A-Hap-1/2, Ta Sus1-7B-Hap-T, Ta AGP-S1-7A-1/2 and Ta AGP-L-1B-Hap-1/2/3) had additive effect of TKW in Chinese wheat populations. Numbers of favored haplotypes were increased in the breeding process, yet the frequency of favored haplotype combinations was less than that of European and North American cultivars. Selections on these haplotypes were necessary in the future breeding.