The Improvement Of Drought Tolerance In Transgenic Tobacco By Drought-inducible Expression Of Wheat F-box Gene TaFBA1

Drought is the major limiting factor in plant growth and development, and can greatly affect crop production. There are many pathways evolved in plants to improve the drought tolerance under water-deficit conditions. The ubiquitin-26 S proteasome system(UPS) plays an important role in the resistance of plants to abiotic stresses. E3 acts as a central component in the ubiquitination process. The SCF complex is a key E3 legases. F-box, as a major subunit of the SCF complex, plays an essential role in the recognition of the substrate. Meanwhile, F-box proteins are also important in response to biotic and abiotic stresses.In our previous study, we had cloned a F-box gene, named Ta FBA1. We found the transgenic plants with overexpressed Ta FBA1 under the control of the constitutive 35 S Ca MV promoter had a higher tolerance to drought stress, but displayed a changed phenotype in growth and development under normal conditions. In the present study, the stress-inducible RD29 A promoter was used instead of 35 S promoter for Ta FBA1 overexpression to minimize the effects on plant growth and development. Encouragingly, RD29A::Ta FBA1 transgenic plants exhibited enhanced drought tolerance while avoiding the variation in the development process compared with 35S::Ta FBA1 plants. We investigated the probable mechanism underlying the enhanced drought tolerance in the transgenic tobacco plants.(1) RD29A::Ta FBA1 transgenic tobaccos were obtained and identified by a variety of ways. We found the expression of Ta FBA1 could be induced by drought stress and the degree of the expression increased following the drought stress. Therefore, the transgenic plants can be used in the following assays.(2) Overexpression of Ta FBA1 in transgenic tobacco led to an altered phenotype compared with wild type(WT) under normal condition, while there was no significant difference between transgenic plants and WT at the seedling and adult stages. These suggest inducible expression of Ta FBA1 can eliminate the changed phenotype caused by overexpression of Ta FBA1.(3) Under drought stress, RD29A::Ta FBA1 transgenic tobaccos showed a higher germination rate and a better growth at both seedling stage and adult stage. These indicate than transgenic plants have a higher tolerance to drought stress. Meanwhile, RD29A::Ta FBA1 transgenic tobaccos had a stable photosynthesis compared with WT.(4) Under drought stress, compared with WT, RD29A::Ta FBA1 transgenic tobaccos displayed a high water retention capability. Transgenic tobaccos had higher relative water content(RWC), lower water loss and osmotic potential. Moreover, transgenic tobaccos had higher soluble sugar and proline contents, which indicated that the expression of Ta FBA1 can advance the accumulation of soluble sugar and proline to decrease the osmotic potential. This was benefitial to the water retention and improve the tolerance to drought stress.(5) Under drought stress, compared with WT, RD29A::Ta FBA1 transgenic tobaccos displayed increased antioxidant tolerance with less H2O2 accumulation and O2?ˉ production rate and lower MDA content and electrolyte leakage. RD29A::Ta FBA1 transgenic tobaccos had higher activities of antioxidant enzymes(such as SOD, CAT, APX, POD) and the expression of these enzymes genes was higher in transgenic plants. These results suggested that the reason why transgenic tobaccos had higher oxidative tolerance was transgenic tobaccos had higher antioxidant enzyme activites.(6) We constructed the expression vector pro Ta FBA1::GUS and transformed it into tobacco NC89. Through GUS staining, we found Ta FBA1 was expressed mainly in the leaves and the expression of the gene can be induced by drought stress. This indicated that Ta FBA1 can express in wheat and be inducibed by drought stress, which can improve the drought tolerance in wheat.