Abstract：Abstract S-adenosylmethionine decarboxylase (SAMDC) is a crucial enzyme related to biosynthesis of polyamines (PAs). In this study, the full-length 1 083 bp cDNA sequence of Sesamum indicum (SmSAMDC) (GenBank No. GU983041.1) was amplified from total mRNA of S. miltiorrhiza by RT-PCR and designated as SmSAMDC. Phylogenetic analysis of this deduced protein inferred using the unweighted pair-group method with arithmetic means (UPGMA) method indicated that SmSAMDC was quite similar to SAMDC from other plants, especially S. indicum up to 82%. The SmSAMDC protein showed an obvious homology with other species of plants. To reveal the role of polyamines against drought, the ampli?ed coding sequence of SmSAMDC was overexpressed in tobacco (Nicotiana tabacum). To screen the positive plants, PCR analysis was performed and DNA of the transgenic lines (T0 and T1 plants) was used as templates. RT-PCR analysis was performed using gene-specific primers to screen 5 transgenic plants, and an amplicon of 500 bp was showed. These results clearly demonstrated the overexpression of the SmSAMDC gene in the genome of the transgenic plants. During drought, the growth rates of the wild type and transgenic tobacco significantly decreased, and their development process was also inhibited. However, after 18 d drought treatment, obvious wilting was observed in wild type, meanwhile, much fewer wilting was detected in T1 generation plants of transgenic tobacco from lines S-7, S-8 and S-14 until 18. After rewatering, much more transgenic tobacco plants survived and recovered comparing with the wild type. This results showed that overexpression of SmSAMDC greatly increased the survival rate under drought condition. The physiological study indicated plant lines with SmSAMDC showed a higher relative water content (RWC) and stronger activities of antioxidant enzymes, with lesser contents of malondialdehyde (MDA) and superoxide radical anions (O2·-) compared with the wild type lines under drought condition. To reveal the role of SmSAMDC in preventing membrane injury caused by drought stress, the activities of several antioxidant enzymes, comprising of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were analyzed. And the activities of these enzymes were almost the same between the transgenic lines and wild type in normal growth. However, after 18 d of drought treatment, the activities of SOD and CAT were slightly higher in the transgenic lines than that in wild type, on the other hand, the activities of POD dropped a lot. To further explore the role of SmSAMDC in ROS reduction, the accumulation of O2·- and H2O2 were examined in transgenic lines under drought stress using nitroblue tetrazolium (NBT) and diaminobenzidine (DAB) staining, separately. The staining results indicated that overexpression of SmSAMDC decreased the accumulation of O2·- (NBT staining) and increased H2O2 (DAB staining) under drought stress for 18 d comparing to wild type. Furthermore, the results showed that overexpression of SmSAMDC signi?cantly increased the accumulation of hydrogen peroxide (H2O2) in tobacco under drought stress. These results indicated that overexpression of SmSAMDC increased drought tolerance in tobacco. Furthermore, this is the foundation that SmSAMDC could be applied in other species.
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