A Study On The Quality Properties Of Colored Rice And Molecular Genetics Of The Pericarp Color Character In Rice (Oryza Sativa L.)

Colored rice is a type of rice with pigments deposited in their grain pericarp. The pigments in colored rice pericarp are flavonoids in nature. Proanthocyanidins and anthocyanins are the major flavonoids of the two most common types of colored rice, red rice and purple rice, respectively. White rice that is now grown and consumed throughout the world was domesticated from red rice. In this study, a dozen colored rice lines and one white rice variety were grown in the same condition and their nutritional and functional quality parameters were analyzed; The inheritance of pericarp color of red rice Zhu I was investigated and the gene controlling this characteristic was mapped; The possible domestication route of white pericarp characteristic was explored through polymorphism analysis of one Rc fragment among 221 rice lines from all over the world; The genetic basis of the purple pericarp characteristic was analyzed and the gene controlling this trait was fine mapped; The DNA sequences and RNA expression of the Ra gene, one of the two candidate genes within the delimited region for purple pericarps was analysed. The main results are as follows:1. Analysis of brown rice grains (dehulled rice) of 4 red, 6 purple and one white rice line, which were harvested from plants grown in the same condition, showed that the content of ash, fat, fiber, total starch, mineral elements (Fe, Zn, Ca, Cu, Mn, Mg, Mo), resistant starch, and the relative content of fatty acids and amino acids of white rice was within the range of colored rice. The content of protein, amino acids and phytic acid of all colored rice lines was higher than that of the white rice, but the overall higher content of colored rice must not be caused by pigmentation because no significant correlation between the content of pigments and these components was detected.2. Cyanidin-3-glucoside and peonidin-3-glucoside are the two main constituents of pigment in purple rice pericarp. There are substantial differences of pigment content among purple rice lines with the highest at 12.44mg/g and the lowest at 2.20mg/g. The pericarp extract of colored rices had much higher antioxidant capability than the white rice, e.g. the DPPH scavenging activity of purple rice line NL5-9 was about 13 fold greater than the white line Chiyou S48. There is a positive relationship between DPPH scavenging activity and content of pigments, which indicated that anthocyanins are the main antioxidant component in purple rice.3. The red pericarp characteristic of rice is dominant over white pericarp characteristic. In the F₂ population of Pei'ai 64S (white rice)/ Zhu I (red rice), the segregation ratio of F₂ plants fit in a 1 (colored homozygous) : 2 (colored heterozygous) : 1 (white homozygous) ratio, indicating that a single gene controlled whether the pericarp is colored or not.4. The gene controlling the red pericarp characteristic of Zhu I was mapped on chromosome 7, which was linked with SSR markers RM542, RM8247 at genetic distances of 16.63cM, 4.58cM, respectively. This result matched previously mapped position of the Rc gene .5.. It was reported that a 14-bp deletion within the exon 6 of the Rc gene caused the mutation from red to white color of pericarp. DNA sequencing results showed that Zhu I has the same sequence as IRGC-105491's (red pericarp) and Pei'ai 64S the same as Jefferson's (white pericarp), which indicated that the difference of pericarp color between Zhu I and Pei'ai may also have resulted from the 14bp deletion. Based on the observations that Zhu I has the same Rc sequence as naturally occurring red rice in the very region, and that there was a high percentage of different microsatellite markers between Zhu I and Xieqingzao B, the reported parent variety of Zhu I , it is postulated that the red pericarp characteristic of Zhu I might have resulted from an outcross of Xieqingzao B with an unknown red rice line, instead of a result of a dominant mutation from Xieqingzao B.6. From the 161 white rice lines tested for the 14-bp deletion of the Rc gene, 10 lines don't contain the 14-bp deletion, which suggested that there are at least two domestication routes from red rice to white rice. Most of white rice lines, including white varieties of Oryza glaberrima were domesticated through the first route, which was caused by the14-bp deletion within the exon 6 of the Rc gene. Other white rice varieties, represented by the 10 white rice lines from Afghanistan, Iraq and Pakistan, were evolved through the second route, which is featured by a nonsense mutation C to A within exon 6 of the Rc gene.7. The purple pericarp characteristic of rice is also dominant over white pericarp characteristic. There are differences of pigmentation degree among segregating plants with colored pericarps. The plants segregated in a 3 (bearing colored seeds) :1 (bearing white seeds) ratio in the F₂ population of both Pei'ai 64S /Yunanheixiannuo and Pei'ai 64S /Chuanheinuo, which suggested that only a single gene controlling whether the pericarp is colored or not in both populations.8. The Pb gene that controls the purple pericarp characteristic is mapped to a 25Kb region (TIGR4: chromosome 4: 27712299-2773775) using the F₂ populations of Pei'ai 64S/Yunanheixiannuo and Pei'ai 64S/Chuanheinuo. The delimited region contained two candidate genes, bhlh16 and Ra.9. Sequence analysis showed that the exon 7 of the Ra gene of Yunanheixiannuo and Chuanheinuo had a 2 bp (GT) deletion compared with those of the white rice varieties Pei'ai 64S, 9311 and Nipponbare. A CAPS marker, CAPSRa, was developed according to the GT deletion for analysis of the two F₂ segregating populations and 106 rice lines. The results showed that all F₂ plants with white pericarp, and all non-purple rice lines (63 white and 22 red) don't contain the GT deletion, but all 20 purple rice lines contained the GT deletion. These results suggested that the Ra gene may be the Pb gene and the purple pericarp characteristic of rice is caused by the GT deletion of the Ra gene.