title: Introduction of Wx transgene into rice wx mutants leads to both high- and low-amylose rice.
abstract: 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: Wx(a), which produces a large amount of amylose, and Wx(b), which produces a smaller amount of amylose because of the mutation at the 5' splice site of intron 1. Wx(b) is largely distributed in Japonica cultivars, and high amylose cultivars do not exist in Japonica cultivars. We introduced the cloned Wx(a) 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 Wx(a) 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 Wx(a) 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.
authors.affiliation: Faculty of Agriculture, Niigata University, 8050, Ikarashi 2, Niigata, 950-2181 Japan. kimi@agr.niigata-u.ac.jp
authors.forename: Kimiko
authors.initials: K
authors.lastname: Itoh
authors.forename: Hiroko
authors.initials: H
authors.lastname: Ozaki
authors.forename: Kyoko
authors.initials: K
authors.lastname: Okada
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Hori
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Takeda
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Mitsui
mesh_terms: D000688:Amylose / Q000096:biosynthesis*; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D009154:Mutation; D012275:Oryza / Q000201:enzymology / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D012639:Seeds / Q000201:enzymology / Q000235:genetics; D013214:Starch Synthase / Q000235:genetics* / Q000378:metabolism; D019076:Transgenes / Q000235:genetics* / Q000502:physiology
chemical_list: D010940:Plant Proteins; C060756:waxy protein, plant; D000688:Amylose; D013214:Starch Synthase