Cloning and application of major gene GS5 capable of controlling width and weight of rice grain

The invention belongs to the technical field of plant gene engineering, disclosing a separated and cloned major gene GS5 capable of controlling the width and the weight of a rice grain and the DNA sequence of the allelic gene of the major gene GS5. The DNA sequence is shown as SEQ ID NO.1 (Zhenshan 97B) and SEQ ID NO.3 (H94) and contains 10 exons. The amino acid sequence of the major gene and the amino acid sequence of the allelic gene are shown as SEQ ID NO.2 and SEQ ID NO.4. By using two large-grain rice varieties and two small-grain rice varieties for comparative sequencing, in an approximately 6.1kb range, 22 common base differences exist between the large-grain variety and the small-grain variety, wherein 18 mutations are in a promoter area, 4 mutations are in a code area and 5 amino acids are caused to be changed. By using a transgenic technology, GS5 transgenic rice plants are obtained and express that the width and the weight of the rice grain are obviously improved when being compared with the control width and the control weight of the rice grain. The character changes are quite coincident with the two genotype expressions of a Zhenshan 97 near-isogenic line and a GS5 near-isogenic line. The invention additionally discloses a method of near-isogenic line breeding, gene cloning and gene transfer and application thereof.