Over-expressing GsCBRLK/SCMRP Enhances Alkaline Tolerance and Methionine Content in Transgenic Medicago sativa

Abstract

Drought and saline-alkaline stresses, significantly affect growth and productivity of plants. The reaction of plant to environmental stresses is controlled by numerous genes via transcriptional regulation and protein phosphorylation. A stress-responsive kinase gene, GsCBRLK, has been cloned from a Glycine soja cDNA library under salinity, drought, and cold stresses. Over-expression of GsCBRLK in transgenic Arabidopsis resulted in enhanced tolerance to high salinity and ABA. SCMRP is a kind of storage protein gene coding high-sulfur-containing amino acid. In this study, we constructed an expression vector BEOCBRLK-SCMRP and transformed both GsCBRLK and SCMRP genes into alfalfa. The transgenic alfalfa grew well after NaHCO3 treatment(100 and 150 mmol L–1) for 14 days; whereas, the wild type plants exhibited discoloration and stunted growth, even death. The MDA content and relative membrane permeability caused by alkaline stress in transgenic plants varied significantly compared to those in the wild type(P 0.05). Moreover, the superoxide dismutase(SOD) activity in transgenic plants under alkali stress increased than that of the wild type. Amino acid content assay showed that the transformants had higher methionine content than the non-transformed plants. These results indicated that the transgenic alfalfa carrying both GsCBRLK and SCMRP possesses enhanced alkaline tolerance and rich methionine simultaneously.