Effects On Rice Grain Quality By Interference Of The Expression Of Different Starch Branching Enzymes

Starch is the most important ingredient in rice endosperm, and its composition and structure are the most important factors to determine the quality and feature of rice. In rice endosperm, the starch is made up of amylopectin and amylose, and the starch branching enzyme (SBE) is one of the key enzymes involved in starch biosynthesis.In rice, there are three SBE isoforms, SBEI, SBEIIa (SBE4) and SBEIIb (SBE3). Previous studies had shown that SBEI and SBE3, mainly involved in the amylopectin biosynthesis of endosperm. If the expression of SBEI and SBE3was reduced at the same time, the apparent amylose content (AAC) and the resistant starch (RS) content could increase. SBE4mainly expressed in the leaves, but the formation mechanism for the structure of starch in rice endosperm is not clear.Therefore, based on the gene function study for SBEI and SBE3in our previous works, in this study, we constructed the vectors of SBE4-RN Ai, Anti-SBEl/4, Anti-SBE3/4, and generated a series of transgenic rice in order to analyze the influence on the physical and chemical properties of rice. Moreover, we also anylzed the grain quality of the homozygous transgenic lines containing the SBE3-RNAi, SBEI-RNAi, or Anti-SBE1/3, that our laboratory had been generated. We made a careful analysis and comparison of the starch physicochemical properties among these related transgenic rice. The main results are shown as followings:1. Three vectors, containing SBE4-RNAi, Anti-SBEl/4or Anti-SBE3/4, respectively, were constructed and introduced into the japonica cultivars R-Wuyunjing8and Yandao8by Agrobacterium-mediated transformation. The transgene integration was confirmed by PCR analysis and hygromycin resistance test. The results of RT-PCR analysis revealed that SBE4gene was expressed in all tested tissues with various expression level and the expression of the endogenous target gene(s) was sucussfully decreased in transgenic rice plants. 2. The results of agronomic traits investigation showed that no significant plant morphological changes among transgenic plants, however, the grain shape and weight of some transgenic rice lines changed greatly when compared with those of the wild type. By using scanning electron microscope, the starch granules of some transgenic rice present irregular shape, loosing arrangement, and the surface layer had different degree holes.3. The data of grain quality analyses showed that the AAC and RS content, as well as the thermodynamic properties, changed significantly in the endosperm of some transgenic rice. Especially for the transgenic rice with anti-SBEl/3, anti-SBE4/3, the AAC and RS content increased significantly. But in SBE1-RNAi transgenic rice, there was no effect on the physicochemical qualities. Based on the above data, it might be concluded that, in starch biosynthesis, SBE3plays a major role. Although the function of SBE4remains to be further researched, but the role of SBE4could not be ignored,4. In transgenic rice with only SBE1-RNAi, the thermodynamic properties of starch did not change. But, when interference of the expression of other SBE genes, or inhibiting the expression of two SBE genes at the same time, the thermodynamic properties of starch changed obviously. In transgenic rice with both antisense SBE3and SBE4genes, the peak gelatinization temperature was highest. Accordingly, the solubility and gelatinization properties of starches from some transgenic rice changed obviously when comparied with that of wild type.