The wheat (T. aestivum) sucrose synthase 2 gene (TaSus2) active in endosperm development is associated with yield traits
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Sucrose synthase catalyzes the reaction sucrose + UDP → UDP-glucose + fructose, the first step in the conversion of sucrose to starch in endosperm. Previous studies identified two tissue-specific, yet functionally redundant, sucrose synthase (SUS) genes, Sus1 and Sus2. In the present study, the wheat Sus2 orthologous gene (TaSus2) series was isolated and mapped on chromosomes 2A, 2B, and 2D. Based on sequencing in 61 wheat accessions, three single-nucleotide polymorphisms (SNPs) were detected in TaSus2-2B. These formed two haplotypes (Hap-H and Hap-L), but no diversity was found in either TaSus2-2A or TaSus2-2D. Based on the sequences of the two haplotypes, we developed a co-dominant marker, TaSus2-2B tgw , which amplified 423 or 381-bp fragments in different wheat accessions. TaSus2-2B tgw was located between markers Xbarc102.2 and Xbarc91 on chromosome 2BS in a RIL population from Xiaoyan 54 × Jing 411. Association analysis suggested that the two haplotypes were significantly associated with 1,000 grain weight (TGW) in 89 modern wheat varieties in the Chinese mini-core collection. Mean TGW difference between the two haplotypes over three cropping seasons was 4.26 g (varying from 3.71 to 4.94 g). Comparative genomics analysis detected major kernel weight QTLs not only in the chromosome region containing TaSus2-2B tgw, but also in the collinear regions of TaSus2 on rice chromosome 7 and maize chromosome 9. The preferred Hap-H haplotype for high TGW underwent very strong positive selection in Chinese wheat breeding, but not in Europe. The geographic distribution of Hap-H was perhaps determined by both latitude and the intensity of selection in wheat breeding.
KeywordsTriticum aestivum Sucrose synthase 2 Haplotype Thousand grain weight
We gratefully appreciate the help of Prof. Robert A McIntosh, University of Sydney, with English editing and discussion. Thanks were also given to the group of Prof. Tong YP and Li ZS, Institute of Genetics and Developmental Biology, CAS, for their help in mapping the haplotypes in their RIL population. Thanks were also given to Prof. Liu ZY and Yan JB, China Agricultural University; Mao L, Chinese Academy of Agricultural Sciences, for their help in comparative genetic analysis. This research was supported by the Chinese Ministry of Science and Technology (2010CB125902), funding from Ministry of Agriculture (2008ZX08009) and Modern Agricultural Technical System.
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