Overexpression of GmSnRK1, a soybean sucrose non-fermenting-1 related protein kinase 1 gene, results in directional alteration of carbohydrate metabolism in transgenic Arabidopsis

Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) plays an important role in plant carbohydrate metabolism and starch biosynthesis. The regulatory role of GmSnRK1 from soybean in regulating carbohydrate metabolism and starch accumulation has not been reported. In the present study, a gene encoding the SnRK1 protein, named GmSnRK1, was successfully isolated from soybean, and the functions of this gene were studied. Subcellular localisation analysis in onion epidermal cells indicated that GmSnRK1 protein was localised to the nucleus. The GmSnRK1 gene was introduced into Arabidopsis to obtain transgenic plants. Its overexpression significantly increased the starch content, as well as the sucrose, glucose and fructose content in the transgenic plants compared to the wild-type (WT). Real-time quantitative polymerase chain reaction (PCR) analysis showed that overexpression of GmSnRK1 up-regulated the genes involved in starch biosynthesis, including sucrose synthase (AtSUS), phosphoglucomutase (AtPGM), ADP-glucose pyrophosphorylase (AtAGPase), granule-bound starch synthases (AtGBSS I and AtGBSS II), soluble starch synthases (AtSSS I, AtSSS II, AtSSS III and AtSSS IV) and starch branching enzymes (AtSBE I and AtSBE II) genes. In contrast, the expression of sucrose phosphate synthase (SPS) gene was decreased in the transgenic plants. Meanwhile, the enzyme activity levels of the five starch biosynthetic enzymes (SUS, AGPase, GBSS, SSS and SBE) exhibited higher activities, while the SPS activity was decreased in the transgenic plants compared to WT. These results suggest that the manipulation of GmSnRK1 expression might be used for improving the starch content in engineered plants for biofuel production.