Plant and Cell Physiology, 2003, Vol. 44, No. 5 473-480
© 2003 Oxford University Press
Introduction of Wx Transgene into Rice wx Mutants Leads to Both High- and Low-Amylose Rice
1 Faculty of Agriculture, Niigata University, 8050, Ikarashi 2, Niigata, 950-2181 Japan
2 Faculty of Agriculture, Kagoshima University, 1-21-24 Koorimoto, Kagoshima, 890-0065 Japan
3 Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2, Niigata, 950-2181 Japan
The Waxy (Wx) gene encodes a granule-bound starch synthase (GBSS) that plays a key role in the amylose synthesis of rice and other plant species. Two functional Wx alleles of rice exist: Wxa, which produces a large amount of amylose, and Wxb, which produces a smaller amount of amylose because of the mutation at the 5' splice site of intron 1. Wxb is largely distributed in Japonica cultivars, and high amylose cultivars do not exist in Japonica cultivars. We introduced the cloned Wxa cDNA into null-mutant Japonica rice (wx). The amylose contents of these transgenic plants were 6–11% higher than that of the original cultivar, Labelle, which carries the Wxa allele, although the levels of the Wx protein in the transgenic rice were equal to those of cv. Labelle. We also observed a gene-dosage effect of the Wxa transgene on Wx protein expression, but a smaller dosage effect was observed in amylose production with over 40% of amylose content in transgenic rice. Moreover, one transgenic line carrying eleven copies of the transgene showed low levels of Wx expression and amylose in the endosperm. This suggested that the integration of excessive copies of the transgene might lead to gene silencing.
4 Corresponding author: E-mail, kimi{at}agr.niigata-u.ac.jp; Fax: +81-25-262-6854.
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