The major storage substance in rice endosperm is starch, which accounts for 80% of dry matter weight. In this study, rice mutant flo7, selected from the progeny of Nipponbare's tissue culture, displayed floury and opaque endosperm. Compared with its corresponding wild type(WT) Nipponbare, the mutant flo7 produced longer, narrower, thinner and lighter grains. The levels of glucose, fructose and sucrose in the mutant flo7 endosperm were higher than those in the WT endosperm, whereas the protein content was not affected. With respect to both amylose content and gel consistency, the mutant flo7 was lower than WT, but its alkali value was higher. Scanning electron microscopic examinations showed that the endosperm of the mutant flo7 contained irregular, loosely packed and compound starch granules. Genetic analysis indicated that the mutant phenotype was determined by a single recessive nuclear gene. The flo7 locus was mapped to a region on the long arm of chromosome 12, within a 95.1 kb interval defined by the markers C2-11 and C5-15. There are 13 open reading frames in the mapping interval. Transcription profiling of the developing grains showed that a number of genes involved in starch synthesis were affected differently in the mutant flo7.
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