| Summary: | 碩士 === 國立臺灣大學 === 農藝學研究所 === 101 === Abstract
Rice is the major crop in Taiwan, and the promotion of rice grain quality is an important goal in rice breeding programs. Because starchy endosperm is primary portion of rice grains, endosperm texture and starch granule morphology of rice grains are closely related to grain quality and yield. The comprehensive researches by a series of induced opaque endosperm mutants on genetic analysis, positional cloning and these isolated genes conferring to opaque grains provided new raw breeding material to improve rice grain quality and to breed new rice varieties for multipurpose usage of rice. The characteristics of the opaque endosperm mutants of TK 8 induced by EMS could be generally categorized into three types: waxy, dull, and floury grains according to the amylose contents and starch granule morphologies. The fracture surface of endosperm under scanning electron microscopy revealed that polygonal single starch granule was closely packed without space in translucent portions of endosperm, and the polygonal starch granules were tightly packed containing pores on the inside surface in the opaque portion of waxy mutants. In addotion, in the opaque sections of floury mutants, the single starch granules were round and loosely packed with a lot of air spaces. One novel opaque endosperm mutant line CNY921403 (WY14) exhibits a floury grain. By positional cloning, a nonsynonymous mutation occurred at FLO7 in WY14. The promoter and 3’-UTR region of FLO7 showed DNA diversity between japonica and indica varieties. FLO7 was annotated as a ATP-binding cassette transporter. Furthermore, the number of transmembrane domains of FLO7 protein was predicted 4 in wild type but only 3 in the mutated flo7, in which the nonsynonymous mutation resided in conserved domain among several species. To verify the positional cloning of FLO7, the complementary test was executed by transforming the wild type allele of FLO7 into mutant line WY14, and the T1 seeds of T0 plants were segregated for translucent and opaque endosperm, comfirming that FLO7 gene was responsible for flouy grain. By subcellular localization analysis by transforming the fluorescent protein-target FLO7 protein into rice protoplasts, FLO7 protein was observed in endoplasmic reticulum, Golgi apparatus and proplastids. As the result, the comprehsive research of this novel floury gene FLO7 provides additional information for the factors corresponding to endosperm development and rice quality.
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