Fine Mapping Of Rice Grain Shape Gene GS2.2

Rice grain shape traits, which include grain length, grain width and grain size, were important traits related to both rice yield and quality. Firstly, grain shape of rice grain directly determines grain weight, which influences the yield of rice. Secondary, rice grain shape is an important factor to determine the appearance quality and commercial quality of rice. Thirdly, to breed the sterile line and restorer line with significant difference in grain shape traits, is the key technique suitable for seed mechanical separation processing in the new proposed "the sterile line and restorer line mixed sowing" hybrid rice seed production technology. Therefore, it is of great significance to fine mapping and cloning of grain shape genes, and to breed the rice varieties which meet the requirements of grain size by molecular design. In this paper, a set of near isogenic lines (NIL) was constructed, based the indica rice cultivar, Tedaxian (TDX), which with large size grain as the donor parent, and the japonica rice variety Nipponbare as recurrent parent. A major QTL conferring grain size traits was fine mapped by using the NIL. The function approach on the cellular level of the new QTL to grain shape traits was found also. The main results are as follows:1) The near isogenic lines was constructed, which with the indica rice cultivar TDX as donor parent and the japonica rice variety Nipponbare as recurrent parent, by continuous backcross three times and selfcross three times. The 1000-grain-weight, grain length, grain width and grain width of the NIL was 37.49g,9.18mm,3.39mm and 2.26mm, respectively. Among them, the difference of grain weight, grain weight, grain length, grain width between of the NIL and NPB were significantly at 0.01 level, whereas, the grain thickness was not significant difference. In addition to the traits of plant height, the other agronomic traits were not significant differences in the NIL and NPB. Results indicated that the behavior of large size grains and small size grains were conformed to Mendelian Law of the dominant single gene segregation.2) In the F2 population derived from NIL and NPB, the DNA marks of RM6424, RM318, RM13893, RM13896 and RM5378 located on chromosome 2 were found to linage to the grain shape traits, by using bulked segregation mixture analysis (BSA) method. The target gene, namely GS2.2, was further located near the molecular marker GS7-2, based on the 2887 plants with extremely small size grain.3) It was observation that both of the hull cell length and cell width were significantly different between GS2.2-NIL and NPB. Thus, it was concluded that the function of GS2.2 was increase hull cell length and cell width, and then further increase the grain size.