Combinational transformation of three wheat genes encoding fructan biosynthesis enzymes confers increased fructan content and tolerance to abiotic stresses in tobacco.

Seven kinds of transgenic tobacco plants transformed with combinations of three FBE genes were obtained. The transgenic plants transformed with Ta1-SST + Ta6-SFT genes appeared to have the highest fructan or soluble sugar content and the strongest salt tolerance. Fructan is thought to be one of the important regulators involved in plant tolerance to various abiotic stresses. In this study, wheat-derived genes, Ta1-SST, Ta6-SFT, and Ta1-FFT, encoding fructan biosynthesis enzymes (FBE) were isolated and cloned into vectors modified pBI121 or pZP211. Seven different combinations of the three target genes were transformed into tobacco plants through an Agrobacterium-mediated approach, and transgenic tobacco plants were identified by PCR, ELISA, and Southern blotting. Compared with tobacco plants transformed with other six combinations of the three target genes and with wild-type plants, the transgenic plants transformed with Ta1-SST + Ta6-SFT genes contained the highest fructan and soluble sugar content. All seven types of transgenic tobacco plants displayed a much higher level of tolerance to drought, low temperature, and high salinity compared with the wild type. Differences of drought and low temperature tolerance between the transgenic plants containing a single FBE gene and those harboring two or three FBE genes were not significant, but the salt tolerance level of the transgenic plants with different FBE gene combinations from high to low was: Ta1-SST + Ta6-SFT > Ta1-SST + Ta6-SFT + Ta1-FFT > Ta1-SST + Ta1-FFT > Ta1-SFT + Ta1-FFT > single FBE gene. These results indicated that the tolerances of the transgenic tobacco plants to various abiotic stresses were associated with the transformed target gene combinations and the contents of fructan and soluble sugar contained in the transgenic plants.