Abstract
BackgroundStarch biosynthesis is one of the most important pathways that determine both grain quality and yield in rice (Oryza sativa L.). Sugary endosperm, sugary-1 (sug-1), is a mutant trait for starch biosynthesis. Rice plants carrying sug-1 produce grains that accumulate water-soluble carbohydrates instead of starch, even after maturity. Although this trait enhances the diversity of grain quality, sugary endosperm rice has hardly been commercialized due to the severely wrinkled grains and subsequent problems in milling. This study was conducted to identify the genes responsible for the sug-h phenotype through a map-based cloning technology.ResultsWe induced a mild sugary mutant, sugary-h (sug-h) through the chemical mutagenesis on the Korean japonica cultivar Hwacheong. Grains of the sug-h mutant were translucent and amber-colored, and the endosperm appeared less wrinkled than sug-1, whereas the soluble sugar content was fairly high. These characteristics confer greater marketability to the sug-h mutant. Genetic analyses indicated that the sug-h mutant phenotype was controlled by a complementary interaction of two recessive genes, Isoamylase1 (OsISA1), which was reported previously, and Starch branching enzyme IIa (OsBEIIa), which was newly identified in this study. Complementation tests indicated that OsBEIIa regulated the properties of sugary endosperm.ConclusionsComplementary interactions between the starch biosynthesis genes OsISA1 and OsBEIIa determine the mild sugary endosperm mutant, sugary-h, in rice. Our finding may facilitate the breeding of sugaryendosperm rice for commercial benefit.
Highlights
Starch biosynthesis is one of the most important pathways that determine both grain quality and yield in rice (Oryza sativa L.)
We demonstrated that OsISA1 and OsBEIIa were associated with the genetic modifications that were responsible for the sugary endosperm phenotype
Because a direct function of the OsBEIIa could not have been elucidated yet, we suggest that the amino acid substitutions in OsISA1 and OsBEIIa changed the protein complex or enzyme interaction involved in starch biosynthesis, and might be responsible for the sug-h phenotype affecting amylopectin structure
Summary
Starch biosynthesis is one of the most important pathways that determine both grain quality and yield in rice (Oryza sativa L.). Rice plants carrying sug-1 produce grains that accumulate water-soluble carbohydrates instead of starch, even after maturity. This trait enhances the diversity of grain quality, sugary endosperm rice has hardly been commercialized due to the severely wrinkled grains and subsequent problems in milling. Starch is synthesized by four enzyme classes, with multiple subunits in each class: ADP-glucose pyrophosphorylase (AGPase); starch synthase (SS); starch branching enzyme (BE); and starch debranching enzyme (DBE). Other enzymes, such as phosphorylase (Pho) and disproportionating enzyme, are thought to be involved in starch biosynthesis.
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