The reduction of starch branching enzyme alters properties of starch granules in Arabidopsis
Date Issued
2008
Date
2008
Author(s)
Abstract
Starch branching enzymes catalyze the formation of theα-1,6 linkages within the starch polymer. In regard to their peptide sequences, these SBEs are categorized into three classes named SBEI, SBEII, and SBEIII. Three starch branching enzymes, SBE2.1, SBE2.2, and AtSBEIII, have been found in the genome of Arabidopsis thaliana. In the previous studies, no impact on starch structure was observed in the null AtsbeIII mutants, while only slight modifications in amylopectin structure were detected in sbe2.1 and sbe2.2. In stead of knocking out both SBE2.1 and SBE2.2, which leads to no starch accumulation, the strategy adopted in this study is to knock down both SBE 2.1 and SBE 2.2 in order to analyze the effects of SBE on the characteristics of starch granules. The mutants, resulted from RNA interference, decrease the activity of SBE 2.1 to 20~30% and SBE2.2 to 70~80%, compared to those of wild type. On the whole, the decrease of SBE activity may have more severe effects on SBE RNAi mutants than that of sbe 2.1 or sbe 2.2. In this regard, the dwarf mutants, namely SBE RNAi mutants, contain less amount of starch than that of wild type. Starch granules from plants with SBE RNAi mutants show slight difference from those from wild type regarding to morphology as well as diameter. In terms of amylopectin structure, the distribution of chain lengths of amylopectin from SBE RNAi mutants are reduced at DP 6-10 and are comparably high at DP 26-35, compared to those of wild type. The thermal behaviors of the starches isolated from SBE RNAi mutants have greater gelatinization temperature range than those of wild type, indicating the starch structure from SBE RNAi mutants is less regular.
Subjects
RNA interference
Starch branching enzyme
gelatinization temperature
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