| Starch is one of the most important processed products from agriculture, and it is either enzymatically processed for the production of sweeteners and as raw material for fermentation or channelled to various applications as dry starch. Native or chemically modified starches are utilized in food as well as non-food applications, where the specific physicochemical properties are main determinants for their respective use. In plants, starch consists of two different molecules, amylose and amylopectin. To be able to take the full benefit of the specific properties of either amylose or amylopectin, it is of interesting to develop different plant varieties containing only amylose or amylopectin. Through the manipulation of the genes encoding the starch branching enzymes (SBE), scientists have bred several novel varieties with high amylose content (AC) in maize and potato. But up to now, it wasn't achieved in rice. In present study, several approaches were applied to regulate the amylose content in rice endosperm, including the down-regulation of the Sbe expression via antisense RNA or RNA interference approach. The homozygous transgenic rice was subsequently selected from lots of primary transformants, and the grain quality and its related characters were carefully investigated and shown as followings:1. From the offsprings of the transgenic rice lines derived from the cultivars Wuxiang 9915 and Guanglingxiangnuo, we selected and identified several transgenic rice lines containing the homozygous double antisense-Sbe1/Sbe3, Sbe1-RNAi, or Sbe3-RNAi transgene.2. The results from Western blot analysis showed that the expression of both endogenous Sbe1 and Sbe3 was much lower or fully inhibited in the seeds of transgenic plants containing double antisense-Sbe1/Sbe3 gene when compared with those of the non-transfomed wild type. In the homozygous transgenic rice lines containing Sbe1-RNAi construct, the expression of endogenous Sbe1 gene was much lower than non-transfomed wild type, and the expression of endogenous Sbe3 gene was slightly down-regualted. In the homozygous transgenic rice lines containing Sbe3-RNAi construct, the expression of endogenous Sbe3 gene decreased significantly when compared with that of non-transfomed wild type, but the expression of endogenous Sbe1 gene was slightly up-regualted. We studied the expression of GBSS in different homozygous transgenic rice lines, the results showed that the expression of endogenous Wx gene increased slightly in mature seeds of the plants containing double antisense-Sbe/Sbe3 gene.3. The apparent amylose content (AAC) was measured to much higher in mature seeds of the selected transgenic offsprings from Wuxiang 9915 carrying double antisense-Sbe1/Sbe3 than that of the un-transferred wild type, and the highest reached to 26.96%. In mature seeds of the selected transgenic offsprings from Guanglingxiangnuo carrying Sbe3-RNAi construct, the highest AAC reached to19.73%, 12.5 folds more than non-transfomed wild type. The AAC slightly decreased in mature seeds of the selected transgenic offsprings from both Wuxiang 9915 and Ganglingxiangnuo carrying Sbe1-RNAi homozygous transgene.4. In the mature seeds of transgenic rice plants with down-regulated SBE expression and increased AAC, the gel consistency (GC) became harder after compared with that of non-transformed wild type, but the change of gelatinization temperature (GT) was different among various transgenic lines derived from different varieties. The starch RVA profile of nature seeds from transgenic rice also changed.5. In transgenic rice, there was a significant effect of the down-regulated SBE expression and increased AAC on the structure of the starch granules observed by scanning electron microscope. The results from field trials showed that the rice grain weight of the transgenic rice obviously reduced as its AAC down to very low level and the grain size also became smaller.
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