Overexpression of BcGS2 gene in non-heading Chinese cabbage (Brassica campestris) enhanced GS activity and total amino acid content in transgenic seedlings

• The GS2 gene of non-heading Chinese cabbage was isolated from the leaf.
• Nitrate can be used through BcGS2 pathway beyond at least 30 mM in the leaf.
• Overexpression of BcGS2 leads to the improvement of GS activity and total amino acid content in transgenic seedlings.

BackgroundGlutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of nitrogen (N) assimilation, catalyzing the synthesis of glutamine from ammonium and glutamate. Plants have two types of GS isoenzymes that localize in different compartments: one in cytosol (GS1) and another in plastids/chloroplasts (GS2). GS2 is expressed abundantly in leaf mesophyll cells and converts ammonium taken up by plant leaves to glutamine.ResultsThe GS2 gene cDNA of non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) cultivar ‘Suzhouqing’ was isolated by RT-PCR and (5′/3′)-RACE techniques from the leaf. It was classified as a GS2 homolog by sequence alignment and motif search, and named BcGS2. However, there are no reports on regulation of GS2 from NHCC. The biological characterization of a full-length cDNA encoding GS2 is described in this paper. The objective is to investigate the expression, overexpression and regulation of BcGS2 in non-heading Chinese cabbage. The results suggest that BcGS2 is a novel member of the GS family, possibly involved in the N metabolism of non-heading Chinese cabbage. The BcGS2 expression level of transgenic plants was significantly higher than that of wild type plants. The glutamine synthetase activity and free amino acid content were all significantly improved compared to non-transgenic plants.ConclusionThe above results suggested that BcGS2 is a novel member of the GS family in plants. BcGS2 significantly related to the N assimilation of non-heading Chinese cabbage, demonstrating that this gene plays an important role in NHCC nitrogen metabolism.