The Sucrose Synthase 1 And 2 Genes (TaSus1, TaSus2) Associating With 1000-grain Weight In Wheat(Triticum Aestivum L.)

Wheat (Triticum aestivum L.) is one of the most important cereal crops in the world. The yield of wheat comprises three components, fertility head number, grain number, and thousand grain weight. Continuously raise of wheat yield largely depends on the increase of grain number and thousand grain weight.Starch in the endosperm accounts for 70% of the dry weight grain. The enzyme starch synthase catalyzes the first step in the conversion of sucrose to starch. In this study, two sucrose synthase genes (TaSus1, TaSus2) were genotyped. Several different haplotypes were associated with thousand grain weight (TGW), and the favored haplotypes were tested for their frequency changes during breeding and their geographic distribution was characterized.1. Two wheat Sus orthologous genes (TaSus1 & TaSus2) were isolated and mapped on chromosomes 7A/7B/7D and 2A/2B/2D. TaSus2-2A was mapped on 2AS in a DH population derived from Lumai 14 × Hanxuan 10, which was flanked by SSR markers Xgwm122 and Xgwm328.2. The prediction of protein domains coded by TaSusl and TaSus2 suggested that 70% of the domain was sucrose synthase domain and the other part was glycosyl transferase domain. The protein was distributed in green plants, Eukaryota and Cyanobacteria in taxonomic coverage.3. After resequencing 36 wheat varieties, two SNPs (Single nucleotide polymorphisms) were found in the coded region of TaSus2-2A, which formed two haplotypes, Hap-A and Hap-G. A CAPS (Cleaved amplification polymorphic site) marker was developed to distinguish the two haplotypes. In Chinese wheat mini core collection, the two haplotypes were significantly associated with thousand grain weight. Mean TGW difference between the two haplotypes was 6.4g. In Chinese modern varieties and European varieties, the frequency of TaSus2-2A-Hap-A was increased during past six-decades breeding. It favored the higher latitude region.4. Seven SNPs were found in the coded region of TaSusl-7A, which formed five haplotypes, Hap-1/2/3/4/5. Two CAPS markers and an AS-PCR marker were developed to distinguish the five haplotypes. Mean TGW of Hap-2 was 2.8g higher than that of Hap-1 in the Chinese mini core collection. The frequency of TaSusl-7A-Hap-1 was higher in low latitude regions, but TaSusl-7A-Hap-2 was higher in high latitude regions.5. Six SNPs and one indel (Insertion and deletion) were found in the coded region of TaSusl-7B, which formed two haplotypes, Hap-T and Hap-C. A CAPS marker was developed to distinguish the two haplotypes. In the Chinese mini core collection the two haplotypes were significantly associated with TGW, and mean TGW difference between the two haplotypes was 4.4g. In Chinese modern varieties and European varieties, the frequency of TaSusl-7B-Hap-T was increased during breeding in the past six decades. We found Hap-T favored at higher latitude region.6. Four favored haplotypes at TaSusl and TaSus2, TaSus2-2A-Hap-A, TaSus2-2B-Hap-H, TaSusl-7A-Hap-2 and TaSusl-7B-Hap-T, experenced strong positive selection in breeding, and each of them had different geographical preference. The more on yield effect of a haplotype, the stronger it was selected positively in breeding, which let the favored haplotype fixed in breeding populations.