The GS3 locus located in the pericentromeric region of rice chromosome 3 has been frequently identified as a major QTL for both grain weight (a yield trait) and grain length (a quality trait) in the literature. Near isogenic lines of GS3 were developed by successive crossing and backcrossing Minghui 63 (large grain) with Chuan 7 (small grain), using Minghui 63 as the recurrent parent. Analysis of a random subpopulation of 201 individuals from the BC3F2 progeny confirmed that the GS3 locus explained 80–90% of the variation for grain weight and length in this population. In addition, this locus was resolved as a minor QTL for grain width and thickness. Using 1,384 individuals with recessive phenotype (large grain) from a total of 5,740 BC3F2 plants and 11 molecular markers based on sequence information, GS3 was mapped to a DNA fragment approximately 7.9 kb in length. A full-length cDNA corresponding to the target region was identified, which provided complete sequence information for the GS3 candidate. This gene consists of five exons and encodes 232 amino acids with a putative PEBP-like domain, a transmembrane region, a putative TNFR/NGFR family cysteine-rich domain and a VWFC module. Comparative sequencing analysis identified a nonsense mutation, shared among all the large-grain varieties tested in comparison with the small grain varieties, in the second exon of the putative GS3 gene. This mutation causes a 178-aa truncation in the C-terminus of the predicted protein, suggesting that GS3 may function as a negative regulator for grain size. Cloning of such a gene provided the opportunity for fully characterizing the regulatory mechanism and related processes during grain development.
位于水稻3號染色體著絲粒附件區(qū)域的GS3位點在文獻中經(jīng)常被鑒定為粒重（產(chǎn)量性狀）和粒長（品質(zhì)性狀）的主效QTL。以明恢63（大粒）為輪回親本與川7（小粒）進行連續(xù)雜交和回交，構(gòu)建了GS3的近等基因系。對BC3F2后代的201個隨機個體進行分析表明了GS3解釋了該群體80%-90%的粒重和粒長的變異。另外，該位點還被確定為粒寬和籽粒厚度的微效QTL。從總共5740個BC3F2個體中挑出1384個隱性個體，利用11個分子標(biāo)記將GS3定位在大約長7.9kb的DNA片段。從該目標(biāo)區(qū)域內(nèi)鑒定出了一個全長cDNA，為GS3的候選基因提供了完整的序列信息。該基因含有5個外顯子，編碼一個232個氨基酸的蛋白，含有類PEBP結(jié)構(gòu)域，跨膜區(qū)，TNFR/NGFR家族富含半胱氨酸結(jié)構(gòu)域和VWFC模塊。對GS3基因進行序列比較分析，在第二個外顯子中鑒定出了一個無義突變，與小粒品種相比該突變在所檢測的所有大粒品種中都存在。該突變導(dǎo)致GS3蛋白C端缺失了178個氨基酸，這表明GS3可能是籽粒大小的負調(diào)節(jié)因子。
結(jié)果：GS3是粒長和粒重的主效QTL和粒寬和籽粒厚度的微效QTL；將GS3定位在7.9kb的DNA片段；GS3編碼一個可能的跨膜蛋白；蛋白翻譯提前終止導(dǎo)致了長粒的表型。