Functional characterization of the apple MdSAMDC2 gene by ectopic promoter analysis and over-expression in tobacco

The expression of MdSAMDC2 gene, which encodes S-adenosylmethionine decarboxylase (SAMDC) in apple, was up-regulated by low temperature, salt and drought stresses. To identify its in vivo biological functions in the responses to stresses, the promoter region of MdSAMDC2 was isolated and characterized by analyzing the cis-acting regulatory elements and GUS reporter gene by an Agrobacterium-mediated transformation. GUS activity was enhanced upon salt and cold stresses, indicating that MdSAMDC2 promoter region controls gene transcription under stresses. In parallel, several lines of the transgenic tobacco plants over-expressing MdSAMDC2 were obtained. The contents of three polyamines greatly increased in the transgenic lines compared with the non-transgenic WT control. Upon exposed to low temperature (4 A degrees C), salt (150 and 250 mM NaCl) and osmotic (20 % polyethylene glycol) stresses, transgenic plants produced more free polyamines and more active antioxidative enzymes such as superoxide dismutase and catalase than the WT control. Meanwhile, malondialdehyde content, an indicator for membrane lipid peroxidation, decreased in transgenic plants relative to the WT control. Thus, over-expression of MdSAMDC2 in tobacco conferred tolerance to stresses.