Genetic Analysis And Gene Mapping Of A Null-Allele For Lipoxygenase-3 In Rice Embryos (Oryza Sativa L.)

The absence of lipoxygenase-3(Lox-3) in rice embryos can alleviate the accumulation of stale flavor during storage and enhance the storage stability of rice. The western blot based on monoclonal antibodies against rice embryo Lox-3 was used to identify Lox-3-null varieties previously, but the immunoblotting was expensive and time-consuming, which limited the application of Lox-3-null character in rice breeding. In this report, a novel identification method was developed to screen rice embryos for Lox-3-null, based on the physiology and biochemistry characteristic of Lox-3. The screening of Lox-3-null varieties and the genetic analysis of Lox-3-null character were carried out using the above method. The gene for the absence of Lox-3 was mapped with molecular markers. The results were as follow:1. The development of a novel identification method to screen rice embryos for Lox-3-null and the screening of Lox-3-null varieties in landraces.One simple,rapid and novel identification method was developed to screen rice embryos for Lox-3-null, based on the oxidative ability of hydroperoxides, the catalytic product of Lox-3, and the development ability of Starch-KI.Using the specific inhibitor of lipoxygenase, the color development in the normal Lox-3 varieties were inhibited completely. It verified that this method specifically identified the Lox-3-null character in rice embryos. Using the Lox-3-null and Lox-3 normal varieties, which have been identified using western blot by Suzuki, the manipulation of this method was investigated. Similar result could be obtained in replicated experiments by the new method with good sensitivity.199 rice landraces collected from four regions in China were used to screen the Lox-3-null varieties by the above method. Eleven new varieties from Yunnan province China were identified lacking the Lox-3 in embryos, while all landraces from the otherthree regions China was found with normal Lox-3 activity.2. Genetic analysis and gene mapping of a null-allele for lipoxygenase-3 in rice embryos.The inheritance of Lox-3 in rice embryos was determined by crossing Lox-3-null varieties with rice cultivars having normal Lox-3 activity. The distribution of F2 genotypes for the presence of Lox-3 n heterozygote and absence of Lox-3 fitted the ratio 1:2:1, while the segregation ratio of the BCi generation also gave a good fit to 1:1. These data support the conclusion that the lacking of Lox-3 is inherited as a single recessive trait, which accords with the former result analyzed by western blot.A mapping population of 162 F2 line from a cross between ajavanica variety DawDam, which lacked Lox-3 in its embryo, and an indica variety IRBB7, which had normal Lox-3 activity, was used to detect a null-allele for Lox-3. The gene for the absence of Lox-3 was mapped between C595 and C1351 on the chromosome 3 based on SSR and RFLP analysis, with distances of 15.5cM and 14.2cM, respectively. Therefore, this gene was temporarily designated as lox-3.