Lack of starch synthase IIIa and high expression of granule-bound starch synthase I synergistically increase the apparent amylose content in rice endosperm.
Rice endosperm starch is composed of 0-30% linear amylose, which is entirely synthesized by granule-bound starch synthase I (GBSSI: encoded by Waxy, Wx). The remainder consists of branched amylopectin and is elongated by multiple starch synthases (SS) including SSI, IIa and IIIa. Typical japonica rice lacks active SSIIa and contains a low expressing Wx(b) causing a low amylose content (ca. 20%). WAB2-3 (SS3a/Wx(a)) lines generated by the introduction of a dominant indica Wx(a) into a japonica waxy mutant (SS3a/wx) exhibit elevated GBSSI and amylose content (ca. 25%). The japonica ss3a mutant (ss3a/Wx(b)) shows a high amylose content (ca. 30%), decreased long chains of amylopectin and increased GBSSI levels. To investigate the functional relationship between the ss3a and Wx(a) genes, the ss3a/Wx(a) line was generated by crossing ss3a/Wx(b) with SS3a/Wx(a), and the starch properties of this line were examined. The results show that the apparent amylose content of the ss3a/Wx(a) line was increased (41.3%) compared to the parental lines. However, the GBSSI quantity did not increase compared to the SS3a/Wx(a) line. The amylopectin branch structures were similar to the ss3a/Wx(b) mutant. Therefore, Wx(a) and ss3a synergistically increase the apparent amylose content in rice endosperm, and the possible reasons for this increase are discussed.
Department of Biological Production, Akita Prefectural University, 241-438 Kaidobata-Nishi, Nakano Shimoshinjo, Akita City, Akita 010-0195, Japan. Electronic address: ncrofts@akita-pu.ac.jp.
Naoko
N
Crofts
Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan. Electronic address: f09c001b@gmail.com.
Katsumi
K
Abe
Department of Biological Production, Akita Prefectural University, 241-438 Kaidobata-Nishi, Nakano Shimoshinjo, Akita City, Akita 010-0195, Japan. Electronic address: sound-of-iberty.smash@docomo.ne.jp.
Satomi
S
Aihara
Department of Biological Production, Akita Prefectural University, 241-438 Kaidobata-Nishi, Nakano Shimoshinjo, Akita City, Akita 010-0195, Japan. Electronic address: i---love--strawberry_8.3@docomo.ne.jp.
Rumiko
R
Itoh
Department of Biological Production, Akita Prefectural University, 241-438 Kaidobata-Nishi, Nakano Shimoshinjo, Akita City, Akita 010-0195, Japan. Electronic address: nakayn@akita-pu.ac.jp.
Yasunori
Y
Nakamura
Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan; Center for Transdisciplinary Research Institute, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan. Electronic address: kimi@agr.niigata-u.ac.jp.
Kimiko
K
Itoh
Department of Biological Production, Akita Prefectural University, 241-438 Kaidobata-Nishi, Nakano Shimoshinjo, Akita City, Akita 010-0195, Japan. Electronic address: naokof@akita-pu.ac.jp.
Naoko
N
Fujita
D000687:Amylopectin / Q000096:biosynthesis*; D000688:Amylose / Q000096:biosynthesis*; D056625:Endosperm / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D014644:Genetic Variation; D005838:Genotype; D006006:Glycogen Synthase / Q000378:metabolism*; D009154:Mutation; D012275:Oryza / Q000201:enzymology* / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000378:metabolism; D013214:Starch Synthase / Q000378:metabolism
D000688:Amylose; D000687:Amylopectin; D006006:Glycogen Synthase; D013214:Starch Synthase