| Rice output is increasing as science and technology progressing.The stoage security problem spreads worldwide nowadays. The degradation of paddy lipids mainly occurs in one or two years storage time and it is responsible for the reduction of paddy quality and the production of stale flavor. As temperature and humidity increasing during storage time, the degradation of lipids expedited. It was reported that in China, 5% storage rice, either as food or seeds, were lost during storage time. Many methods are using to prevent the degradation of paddy lipids, including well packaging, microwave treatment, and low temperature storage, etc. Some of them cost much and others are not convenient, And what's mores the methods using today may impact the environment more or less. So a better new resolvent is to breeding storable rice varieties.It is proved that LOX-3, the major component of the isozymes accounting for 80-90% of total activity of LOX in rice embryos, is a key enzyme in the degradation of lipids, and its activity leads to the production of stale flavor. The lack of LOX-3 in rice embryo would decrease lipids peroxidation, and alleviate accumulation of stale flavor during storage time. The study of LOX-3 genetics, using LOX-3-null materials, is necessary for the breeding of storable rice varieties. Genetic survey suggested that the absence of LOX-3 was controlled by a single Mendelian recessive gene. An allelism test between several LOX-3-null varieties was taken and the gene was mapped in this research.1. Allelism testOur laboratory once examined 199 rice varieties from 4 regions, and found 10 embryo LOX-3-null varieties, which were all from Yunnan province. In this study, hybridizations were taken between Daw Dam and the 10 varieties lacking of embryo LOX-3 mentioned above. A simple, rapid and novel identification method called I2-KI screening method was developed by our laboratory to screen paddy embryos for LOX-3-null. Generating seeds were used to analyze the variation of theLOX-3-null in embryos, using I2-KI screening method. The results indicats that the lacking of LOX-3 in these 11 varieties are allelic, i.e., the 10 varieties contain the same recessive gene lox-3 with Daw Dam.2. LOX-3 gene fine mapping. In this research, a jovanica variety Daw Dam, which is proved lacking of LOX-3 in embryo, was crossed with an indica variety IRBB7, which has normal LOX-3 activity in embryo. And another japanica variety PL2, which is also a LOX-3 lacking material, was crossed with an indica Variety 9311, which has normal embryo LOX-3 activity, to build two F2 populations.I2-KI screening method was used to survey the distribution for absence phenotypes of LOX-3 in F2 populations. Detecting F2:3 lines, LOX-3-null ones were found and used as mapping populations.641 of the 3044 Daw Dam/IRBB7 F2 populatioin, which display absence of LOX-3 phenotype, were used as fine mapping population. Analysis was performed in conjunction with molecular markers. Data were collected and the linkage map was constructed. The gene, temporarily designated as lox-3, was located between SSR markers RM3405 and SSR3-183 on chromosome 3, with distances of 0.46cM and 0.15cM, respectively. More work was done to build both gene linkage map and physical map. A gene forecasting was taken, and found 5 ORFs in the mapping area, including 2 pupative LOX ORFs. |
