Granule-bound starch synthase 1 (GBSS1) is responsible for amylose synthesis in cereals, and this enzyme is regulated at the transcriptional and post-transcriptional levels. In this study, we show that GBSS1 from Oryza sativa L. (OsGBSS1) can form oligomers in rice endosperm, and oligomerized OsGBSS1 exhibits much higher specific enzymatic activity than the monomer. A monomer-oligomer transition equilibrium for OsGBSS1 occurs in the endosperm during development. Redox potential is a key factor affecting the oligomer percentage as well as the enzymatic activity of OsGBSS1. Adenosine diphosphate glucose, the direct donor of glucose, also impacts OsGBSS1 oligomerization in a concentration-dependent manner. OsGBSS1 oligomerization is influenced by phosphorylation status, which was strongly enhanced by Mitogen-activated protein kinase (MAPK) and ATP treatment and was sharply weakened by protein phosphatase (PPase) treatment. The activity of OsGBSS1 affects the ratio of amylose to amylopectin and therefore the eating quality of rice. Understanding the regulation of OsGBSS1 activity may lead to the improvement of rice eating quality.
Keywords: 3-(cyclohexylamino)-1-propanesulfonic acid; 5,5′-dithiobis-(2-nitrobenzoic acid); ADP-glucose pyrophosphorylase; ADPG; AGPase; CAPS; DBE; DPA; DTNB; DTT; ELC; ELISA; Eating quality; GSH; GST; IPTG; MAPK; NADP; NADPH; NADPH-dependent thioredoxin reductase; NTRC,; Ni-NTA; Oligomerization; Oryza sativa granule-bound starch synthase 1; OsGBSS1; PMSF; PPase; PVDF; Rice; SBE; SP; SS; Specific enzyme activity; adenosine diphosphate glucose; days past anthesis; dl-dithiothreitol; enzyme-linked immunosorbent assay; extra-long unit chain; glutathione S-transferase; isopropyl beta-d-thiogalactopyranoside; lambda protein phosphatase; mOsGBSS1; mature OsGBSS1; mitogen activated protein kinase; nickel nitrilotriacetic; nicotinamide–adenine dinucleotide phosphate; phenylmethanesulfonyl fluoride; poly(vinylidene difluoride); reduced glutathione; reduced nicotinamide–adenine dinucleotide phosphate; starch branching enzyme; starch debranching enzyme; starch phosphorylatase; starch synthase; γ-ECS/GCS; γ-GS/GSHS; γ-glutamylcysteine synthetase; γ-glutathione synthetase.
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