Phenotypic Analysis And Gene Fine Mapping Of Rice Floury Endosperm Mutant Q9

Starch is one of the major storage materials in rice, whose structure and character affect the appearance and eating quality of rice.Nowadays, improving rice quality and enhancing the international competitiveness of rice has become an important issue of rice genetics and molecular breeding in China. Cloning and analyzing floury genes by map-based cloning can explain both the synthesis and regulatory mechanisms of rice starch, which has practical and theoretical significance.Using a rice floury endosperm mutant q9 derived from a landrace Dongbeixiangmi by radiation, this study was conducted including phenotypic observation, physiological, biochemical and genetic analysis. In addition,the gene q9 was fine mapped by map-based cloning strategy. The main results were as follows:(1) The dehulled seeds of q9 were opaque. Compared with the wild type, both the 1,000-grain weight and the total starch content of q9 significantly decreased,amylose content increased, sucrose content decreased, while glucose and fructose content rised, total protein content rised.(2) Dry material accumulation during the mikling process showed that, the single grain weigh of q9 was lighter than that of the wild-type.(3) SEM(scanning electron microscopy) showed starch granules of Dongbeixiangmi were polygonal and densely arranged in uniform size, while starch granules of q9 was round with uneven size and dispersed arrangement(4) SDS-PAGE analysis indicated that the total storage protein of q9 grain was similar to that of Dongbeixiangmi.(5) The chain length distribution of amylopectin suggested that, the fine structure of amylopectin in q9 changed, compared with the wild type. The proportion of short chains (DP 7-9) increased, while the proportion of DP10-17 chains reduced.(6) The starch granules of both q9 and wild type began to swell when the concentration of urea was 5M though the swelling volume of q9 was smaller than that of the wild type.(7) The viscosity profile analysis showed that compared with Dongbeixianngmi, q9 exhibited decreased peak viscosity, hot paste viscosity, breakdown viscosity, and cold paste viscosity as well as increased setback viscosity and pasting temperature, indicating the poor quality of q9.(8) Genetic analysis showed that, in the F2 population derived from the cross between q9 and the wild type, the segregation ratio of seeds showing normal and dehulled phenotype followed Mendelian pattern, i.e.3:1, indicating that the phenotype of q9 was controlled by a single recessive gene.(9) Using a F2 population of q9/Dular (200 plants), the gene q9 was primarily localized within a region of 27.4cM on the short arm of Chromosome 2. Using F2:3 and F3:4 populations of q9/Dular (7548 plants), q9 was fine-mapped within a region around 142kb.Based on current reports, the gene q9 is a new gene conferring floury endosperm.