title: Impact of down-regulation of starch branching enzyme IIb in rice by artificial microRNA- and hairpin RNA-mediated RNA silencing.
abstract: The inactivation of starch branching IIb (SBEIIb) in rice is traditionally associated with elevated apparent amylose content, increased peak gelatinization temperature, and a decreased proportion of short amylopectin branches. To elucidate further the structural and functional role of this enzyme, the phenotypic effects of down-regulating SBEIIb expression in rice endosperm were characterized by artificial microRNA (amiRNA) and hairpin RNA (hp-RNA) gene silencing. The results showed that RNA silencing of SBEIIb expression in rice grains did not affect the expression of other major isoforms of starch branching enzymes or starch synthases. Structural analyses of debranched starch showed that the doubling of apparent amylose content was not due to an increase in the relative proportion of amylose chains but instead was due to significantly elevated levels of long amylopectin and intermediate chains. Rices altered by the amiRNA technique produced a more extreme starch phenotype than those modified using the hp-RNA technique, with a greater increase in the proportion of long amylopectin and intermediate chains. The more pronounced starch structural modifications produced in the amiRNA lines led to more severe alterations in starch granule morphology and crystallinity as well as digestibility of freshly cooked grains. The potential role of attenuating SBEIIb expression in generating starch with elevated levels of resistant starch and lower glycaemic index is discussed.
authors.affiliation: CSIRO Food Futures Flagship, GPO Box 93, North Ryde, NSW 1670, Australia.
authors.forename: Vito M
authors.initials: VM
authors.lastname: Butardo
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Fitzgerald
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Bird
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gidley
authors.forename: Bernadine M
authors.initials: BM
authors.lastname: Flanagan
authors.forename: Oscar
authors.initials: O
authors.lastname: Larroque
authors.forename: Adoracion P
authors.initials: AP
authors.lastname: Resurreccion
authors.forename: Hunter K C
authors.initials: HK
authors.lastname: Laidlaw
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Jobling
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Morell
authors.forename: Sadequr
authors.initials: S
authors.lastname: Rahman
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D055029:Inverted Repeat Sequences; D035683:MicroRNAs / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D013213:Starch / Q000096:biosynthesis / Q000737:chemistry
chemical_list: D035683:MicroRNAs; D010940:Plant Proteins; D013213:Starch; D015061:1,4-alpha-Glucan Branching Enzyme; C116400:starch-branching enzyme IIb