Plant and Cell Physiology Advance Access originally published online on April 20, 2009
Plant and Cell Physiology 2009 50(6):1062-1074; doi:10.1093/pcp/pcp058
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Chlorella Starch Branching Enzyme II (BEII) Can Complement the Function of BEIIb in Rice Endosperm
1CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama, 332-0012 Japan
2Akita Prefectural University, Shimoshinjo-Nakano, Akita-city, 010-0195 Japan
3Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo, 192-0392 Japan
4Kyusyu University, Hakozaki, Fukuoka, 812-8581 Japan
*Corresponding author: E-mail, nakayn{at}akita-pu.ac.jp; Fax, +81-18-872-1681.
| Abstract |
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In monocots, starch branching enzyme II (BEII) was functionally differentiated into BEIIa and BEIIb after separation from the dicots, and in cereals BEIIb plays a distinct role in amylopectin biosynthesis in the endosperm. The present study was conducted to examine to what extent a green algal BEII has an overlapping function with BEIIb in starch biosynthesis by introducing the Chlorella BEII gene into an amylose-extender (ae) mutant of rice. Chlorella BEII was found to complement the contribution of the rice endosperm BEIIb to the structures of amylopectin and starch granules because these mutated phenotypes were recovered almost completely to those of the wild type by the expression of Chlorella BEII. When the recombinant BE enzymes were incubated with the rice ae amylopectin, the branching pattern of Chlorella BEII was much more similar to that of rice BEIIb rather than rice BEIIa. Detailed analyses of BE reaction products suggests that BEIIb and Chlorella BEII only transfer chains with a degree of polymerization (DP) of 6 and 7, whereas BEIIa preferably transfers short chains with a DP of about 6–11. These results show that the Chlorella BEII is functionally similar to rice BEIIb rather than BEIIa.
Keywords: Amylopectin - Chlorella - Rice - Starch - Starch branching enzyme
Abbreviations: ae, amylose-extender; BE, starch branching enzyme; DP, degree of polymerization; DSC, differential scanning calorimetry; DTT, dithiothreitol; SEM, scanning electron microscopy; SS, starch synthase.
(Received February 2, 2009; Accepted April 14, 2009)
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