Phenotypic Analysis And Gene Mapping Of Rice Dull Mutant W54

The endosperm is the main edible part and also an important storage organ of starch and protein in rice seeds.The content and physicochemical properties of starch in endosperm are the decisive factors of yield and eating quality of rice.Characterizing genes controlling starch biosynthesis by map-based cloning using mutants can dissect regulatory mechanisms of rice starch,which has practical and theoretical significance.We obtained a dull mutant w54 from MNU mutants of the japonica variety cv.Koshihikari.Phenotyping,genetic,physiological and biochemical analyses were performed on the w54 mutant in this study.In addition,the mutant gene in w54 was fine mapped by map-based cloning strategy.The main results are as follows:[1]The w54 mutant showed milky and translucent endosperm(dull).When stained with I2-KI,the cross sections of both w54 and wild type seeds exhibited dark blue.Compared with the wild type,the 1000-grain weight of w54 decreased significantly,while no significant difference was observed in other major agronomic traits.[2]SEM(scanning electron microscopy)showed starch granules of Koshihikari were polygonal and arranged closely,as was the case with those of the w54 mutant.The semi-thin sections also showed that there was no significant difference in size and shape of compound starch granules between the wild type and w54.[3]The amylose content decreased significantly in the w54 mutant,only 45.1%of that of wild type.The total protein and starch contents as well as storage protein components in the w54 mutant were not significantly different from those of the wild type.[4]The chain length distribution analysis of amylopectin showed that compared with the wild type,the proportions of chains with DP 6-8 and 16-28 increased,while the proportions of chains with DP9-15 reduced in the w54 mutant.[5]Gelatinization properties analysis showed that the swollen volume of the w54 mutant was almost the same as that of wild type in the low concentration of urea solution(0-4 M).The swollen volume enlarged with the increasing concentration,and the apparent difference occurred at 7 M.[6]Comparison of the viscosity profile between Koshihikari and w54 showed that peak viscosity,breakdown viscosity,cold paste viscosity,and peak time of w54 decreased,while hot paste viscosity and setback viscosity increased,indicating the change in the quality of w54.[7]Compared with the wild type,the expression level and protein content of Wx in the w54 mutant were decreased,indicating the mutated gene might influence the transcription or processing of Wx gene.[8]Genetic analysis showed that,the segregation ratio of seeds showing normal and dull phenotype followed Mendelian pattern,i.e.3:1 in the population of genetic analysis,which indicated that the phenotype of w54 was controlled by a single recessive gene.[9]The w54 locus was maped within a 269 kb genomic region beween markers W57 and W64 on the long arm of Chromosome 6 by using 695 recessive extreme individuals.Based on current reports,the gene w54 could be a new gene du(12)t conferring dull endosperm,which is not yet cloned.In addition,we identified a small-grain dwarf mutant sgd1(t)gene as the multiple allele of BC12/GDD1.