Toward Positional Cloning of the Rice (Oryza sativa L.) Dull 8, Du8
Date Issued
2009
Date
2009
Author(s)
Lin, Hung-Ying
Abstract
Rice is one of the major crops in the world, and it is also a major food in Taiwan. The aim of rice production has been changed from quantity-oriented to quality-oriented because of altered rice consumption along with rapid development of economics and of joining WTO in Taiwan. Researches and breeding for improvement of the rice quality have been the important tasks ever since. The amylose content is one of important factors that affect the quality of rice grain. Low-amylose rice is mostly popular and widely accepted in Japan, Korea and Taiwan, which tends to show fluffy texture and glossy appearance after cooked. In this research, we selected 13 mutant lines of Taikeng 8 (TK8) induced by EMS that were provided by Dr. Yong-Pei Wu. The amylose contents of 13 lines were measured by the absorbance of spectrophotometer at 620 nm after iodine-binding procedures and ranged from 5.11% to 15.53%. The endosperm was stained with iodine which the color of endosperm was proportion to the amylose content. To understand what caused the changes of endosperm color and amylose content, we selected the mutant line CNY921391 for which good taste and low-amylose content of 11.92%. The starch granules of CNY921391, rather than in polyhedron shapes as of TK8, were in sphere shapes by SEM at 3000 X. We established an F2 population by crossing CNY921391 with O. sativa ssp. indica cv. Taichung Sen 17 (TCS17) for applying positional cloning this mutated dull gene. The ratio of transparent endosperm to opaque endosperm was found to be 3.6:1, knowing that this mutant gene is a recessive allele. A total of 30 F2 individuals with opaque endosperm were genotyped with 96 polymorphic markers and subjected for construction of genetic maps with an average interval of 16.63 cM. After linkage analysis, the dull gene was coarsely mapped between S13714 and C53391on the long arm of the chromosome 4 and named the mutated gene as Du8. We proceeded fine mapping by using 26 recombinants and narrowed down the target region between CH0422 and CH0426 encompassing 152987 bp and 12 candidate genes after annotation. We accomplished the fine mapping to narrow down candidate genes to 12, which paved a way to achieve final goal. In the future, high-resolution mapping and DNA sequence candidate genes will be implemented to touch down Du8. Consequently, we can elucidate the gene regulations of dull and metabolism of starch, and further apply in rice breeding to promote rice quality.
Subjects
rice
positional cloning
amylose
dull
Type
thesis
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