An isopentyl transferase gene driven by the senescence-inducible SAG12 promoter improves salinity stress tolerance in cotton

Background: Soil salinity seriously affects cotton growth, leading to the reduction of yield and fiber quality. Recently, genetic engineering has become an efficient tool to increase abiotic stress tolerance in crops. Results: In this study, isopentyl transferase (IPT), a key enzyme involved in cytokinin (CTK) biosynthesis from Agrobacterium tumefaciens, was selected to generate transgenic cotton via Agrobacterium-mediated transformation. A senescence-inducible SAG12 promoter from Arabidopsis was fused with the IPT gene. Ectopic-expression of SAG12::IPT significantly promoted seed germination or seedling tolerance to salt stress. Two IPT transgenic lines, OE3 as a tolerant line during seed germination, and OE8 as a tolerant line at seedling stage, were selected for further physiological analysis. The data showed that ectopic-expression of SAG12::IPT induced the accumulation of CTKs not only in leaves and roots, but also in germinating seeds. Moreover, ectopic-expressing IPT increased the activity of antioxidant enzymes, which was associated with the less reactive oxygen species (ROS) accumulation compared with control plants. Also, ectopic-expression of IPT produced higher K+/Na+ ratio in cotton shoot and root. Conclusion: The senescence-induced CTK accumulation in cotton seeds and seedlings positively regulates salt stress partially by elevating ROS scavenging capability.