title: Elongated phytoglycogen chain length in transgenic rice endosperm expressing active starch synthase IIa affects the altered solubility and crystallinity of the storage α-glucan.
abstract: The relationship between the solubility, crystallinity, and length of the unit chains of plant storage α-glucan was investigated by manipulating the chain length of α-glucans accumulated in a rice mutant. Transgenic lines were produced by introducing a cDNA for starch synthase IIa (SSIIa) from an indica cultivar (SSIIa (I), coding for active SSIIa) into an isoamylase1 (ISA1)-deficient mutant (isa1) that was derived from a japonica cultivar (bearing inactive SSIIa proteins). The water-soluble fraction accounted for >95% of the total α-glucan in the isa1 mutant, whereas it was only 35-70% in the transgenic SSIIa (I)/isa1 lines. Thus, the α-glucans from the SSIIa (I)/isa1 lines were fractionated into soluble and insoluble fractions prior to the following characterizations. X-ray diffraction analysis revealed a weak B-type crystallinity for the α-glucans of the insoluble fraction, while no crystallinity was confirmed for α-glucans in isa1. Concerning the degree of polymerization (DP) ≤30, the chain lengths of these α-glucans differed significantly in the order of SSIIa (I)/isa1 insoluble > SSIIa (I)/isa1 soluble > α-glucans in isa1. The amount of long chains with DP ≥33 was higher in the insoluble fraction α-glucans than in the other two α-glucans. No difference was observed in the chain length distributions of the β-amylase limit dextrins among these α-glucans. These results suggest that in the SSIIa (I)/isa1 transgenic lines, the unit chains of α-glucans were elongated by SSIIa(I), whereas the expression of SSIIa(I) did not affect the branch positions. Thus, the observed insolubility and crystallinity of the insoluble fraction can be attributed to the elongated length of the outer chains due to SSIIa(I).
authors.affiliation: Department of Biological Production, Akita Prefectural University, Akita City, Akita, 010-0195 Japan. naokof@akita-pu.ac.jp
authors.forename: Naoko
authors.initials: N
authors.lastname: Fujita
authors.forename: Isao
authors.initials: I
authors.lastname: Hanashiro
authors.forename: Sachi
authors.initials: S
authors.lastname: Suzuki
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Higuchi
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Toyosawa
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Utsumi
authors.forename: Rumiko
authors.initials: R
authors.lastname: Itoh
authors.forename: Satomi
authors.initials: S
authors.lastname: Aihara
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Nakamura
mesh_terms: D003460:Crystallization; D056625:Endosperm / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D012995:Solubility; D013214:Starch Synthase / Q000235:genetics* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D005936:Glucans; D010940:Plant Proteins; D006003:Glycogen; C111377:starch synthase II; D013214:Starch Synthase