Constitutive And Salt-inducible Expression Of BADH Gene In Transgenic Tomato(Solanum Lycopersicum L. Cv. Micro-Tom) Enhances Salt Tolerance

In genetic engineering of plant resistance, many genes including transcription factors have been expressed in transgenic plants using either constitutive or stress-inducible promoters. Transgenic plants that show strong constitutive expression of transcription factors often suffer from many undesirable phenotypes, such as stunted growth and reduced yield.However, stress-inducible promoters can drive exogenous gene higher expressed in transgenic plants under stress and increase its tolerance without affecting its growth and yield.Betaine aldehyde dehydrogenase (BADH) is the key enzyme for betaine synthesis. Betaine is regarded as being a kind of small, non-toxic osmoprotectant and plays an important role in plant salt-tolerance.BADH expression is induced by salinity and its expression is related to its promoter (P5:-300-+62bp). P5is a salt-induced promoter.In the present study, BADH gene was cloned from Suaeda liaotungensis and, controlled by the Cauliflower mosaic virus (CaMV)35S promoter and stress-inducible P5promoter, transformed into tomato(Solanum lycopersicum) using a leaf regeneration system. Real-time PCR was performed to determine the BADH copy number in the obtained transgenic plants, and single copy transgenic plants were selected. Then through real-time PCR to detect expression of BADHmRNA driven by the two promoters in the single copy transgenic plants. Compare the salt tolerance and growing performance of P5:BADH plants and CaMV35S:BADH plants, the main results are as follows:1. P5:BADH and CaMV35S:BADH were transferred into Micro-Tom via Agrobacterium-mediated leaf disk transformation.400seeds were used in the experiment, and about90plants regenerated plantlet were obtainted.2.16independent Hy-resistant transgenic plants screened by PCR were chosen for determination of BADH copy number by real-time PCR. Three lines of P5:BADH transgenic plants and one line of CaMV35S:BADH transgenic plants contained a single copy of BADH.3. Plants were treated with0,100and200mM NaCl for24h. Real time PCR showed the BADH mRNA level of the plants driven by the P5promoter increased2.3-fold when exposed to100mM NaCl and3-fold in response to200mM NaCl. Under salt stress, the expression of BADH in P5:BADH plants was much higher than that in CaMV35S:BADH plants 4. After7days of salt stress by treatment with200mM NaCl, NT plants had wilted, whereas transgenic plants were healthy and turgid.5. Growth of NT plants, P5:BADH and CaMV35S:BADH transgenic tomato Micro-Tom plants in growing medium, in1/10MS liquid medium, and in soil. Compared to the NT plants, CaMV35S:BADH plants showed highly stunted growth, abscission of flowers and lower yield, whereas P5:BADH plants grew normally as the NT plants.