A tomato plastidic ATP/ADP transporter gene SlAATP increases starch content in transgenic Arabidopsis

A plastidic ATP/ADP transporter (AATP) is responsible for importing ATP from the cytosol into plastids. Increasing the ATP supply is a potential way to facilitate anabolic synthesis in heterotrophic plastids of plants. In this work, a gene encoding the AATP protein, named SlAATP, was successfully isolated from tomato. Expression of SlAATP was induced by exogenous sucrose treatment in tomato. The coding region of SlAATP was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis to obtain transgenic plants. Constitutive expression of SlAATP significantly increased the starch accumulation in the transgenic plants. Real-time quantitative PCR (qRT-PCR) analysis showed that constitutive expression of StAATP up-regulated the expression of phosphoglucomutase (AtPGM), ADP-glucose pyrophosphorylase (AtAGPase), granule-bound starch synthase (AtGBSS I and AtGBSS II), soluble starch synthases (AtSSS I, AtSSS II, AtSSS III and AtSSS IV) and starch branching enzyme (AtSBE I and AtSBE II) genes involved in starch biosynthesis in the transgenic Arabidopsis plants. Meanwhile, enzymatic analyses indicated that the major enzymes (AGPase, GBSS, SSS and SBE) involved in the starch biosynthesis exhibited higher activities in the transgenic plants compared to the wild-type (WT). These findings suggest that SlAATP may improve starch content of Arabidopsis by up-regulating the expression of the related genes and increasing the activities of the major enzymes invovled in starch biosynthesis. The manipulation of SlAATP expression might be used for increasing starch accumulation of plants in the future.