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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Complementation of sugary-1 Phenotype in Rice Endosperm with the Wheat Isoamylase1 Gene Supports a Direct Role for Isoamylase1 in Amylopectin Biosynthesis

Akita Prefectural University, Akita 010–0195, Japan (A.K., Y.U., Y.N.); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi, Saitama 332–0012, Japan (A.K., Y.U., Y.N.); Commonwealth Scientific and Industrial Research Organisation, Plant Industry, Australian Capital Territory 2601, Australia (S.R., Z.L., C.K.-R., M.M.); Osaka Kyoiku University, Kashiwara, Osaka 582–8582, Japan (Y.M.); Kansai University of Welfare Sciences, Kashiwara, Osaka 582–0026, Japan (M.Y.); University of Tokyo, Kashiwa, Chiba 277–8562, Japan (M.U.); Chiba University, Chiba 271–8510, Japan (K.H.); and Kyushu University, Higashi-ku, Fukuoka 812–8581, Japan (H.S.)

To examine the role of isoamylase1 (ISA1) in amylopectin biosynthesis in plants, a genomic DNA fragment from Aegilops tauschii was introduced into the ISA1-deficient rice (Oryza sativa) sugary-1 mutant line EM914, in which endosperm starch is completely replaced by phytoglycogen. A. tauschii is the D genome donor of wheat (Triticum aestivum), and the introduced fragment effectively included the gene for ISA1 for wheat (TaISA1) that was encoded on the D genome. In TaISA1-expressing rice endosperm, phytoglycogen synthesis was substantially replaced by starch synthesis, leaving only residual levels of phytoglycogen. The levels of residual phytoglycogen present were inversely proportional to the expression level of the TaISA1 protein, although the level of pullulanase that had been reduced in EM914 was restored to the same level as that in the wild type. Small but significant differences were found in the amylopectin chain-length distribution, gelatinization temperatures, and A-type x-ray diffraction patterns of the starches from lines expressing TaISA1 when compared with wild-type rice starch, although in the first two parameters, the effect was proportional to the expression level of TaISA. The impact of expression levels of ISA1 on starch structure and properties provides support for the view that ISA1 is directly involved in the synthesis of amylopectin.

^* Corresponding author; e-mail nakayn{at}akita-pu.ac.jp; fax 81–18–872–1681.

Received August 9, 2004; returned for revision October 27, 2004; accepted October 29, 2004.

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