The Improvement Of Osmotic Tolerance In Transgenic Tobacco And Arabidopsis Plants By Root-specific Expression Of Wheat Expansin Gene TaEXPB23

Drought is a major limiting factor in agricultural production systems because it preventscrops from achieving their genetically determined theoretical maximum yields. Recently, thisdisaster becomes more and more severe and frequent. Wheat (Triticum aestivum L) is theimportant food crop worldwide. Water deficit is one of common stresses during wheat growth,and the lost of wheat yield by water deficit is very large. Therefore, it is very important andsignificant to study he mechanism of drought tolerance in wheat in order to increaseproduction under drought stress.In our lab, we had cloned an expansin gene, named TaEXPB23(GenBank accession No.AY260547). In our previous study, transgenic tobacco plants constitutively overexpressingthe wheat β-expansin gene TaEXPB23, under the control of the35S promoter, can enhancedrought tolerance and form a larger root system. However, transgenic tobacco plants haveseverely retarded growth under normal conditions, such as, the grow was faster with largerleaves at early stage; but with shortened height, less leaves, longer internodes, smaller leaves,shortened lifecycle at all at late stage. To reduce the negative effects, in the current study, wegenerated transgenic tobacco plants with root-specific expressing TaEXPB23. The mainresults are as follows:(1) First, we cloned the root-specific expression promoter from Arabidopsis. To obtainstable transgenic lines with root-specific TaEXPB23expression in the roots, the full-lengthcDNA of this gene was positioned under transcriptional control of the PYK10promoter(called P10in the following). PYK10has been described as strongly expressed in root. Thegene construct was transformed into tobacco NC89and Arabidopsis through theAgrobacterium-mediated transformation method.(2) Mature transgenic plants had a larger root system than WT plants. The dry biomass ofroot systems of the tested P10::TaEXPB23transgenic lines was40-50%higher than that of WT plants. Consequently, the root-to-shoot biomass ratio was increased in P10::TaEXPB23transgenic lines. In contrast with the strong increase in root development, the shootdevelopment of P10::TaEXPB23transgenic lines was in accordance with the WT. A detailedquantitative analysis of stem elongation, number of leaves formed at last, and the time offlowering revealed no or only minor difference between the WT and P10::TaEXPB23transgenic lines.(3) Under water stress, P10::TaEXPB23transgenic lines showed a significantly highergermination rate and a better seedling growth.(4) The transgenic tobacco plants could maintain higher photosynthetic rate (Pn), actualefficiency (ФPSII) than WT under water stress(5) Under water stress, transgenic tobacco plants kept a relatively good growth status, incomparison with the withered status in WT. All P10::TaEXPB23plants had higher RWC inthe leaf tissues than WT after exposure to water stress, implying that P10::TaEXPB23couldkeep a higher water level than WT under water stress. Also, at any time point within6h ofdehydration, the three transgenic lines lost remarkably less water compared with WT.(6) P10::TaEXPB23transgenic lines displayed increases antioxidant tolerance underwater stress, with less H2O2accumulation and higher activities of antioxidant enzymes (CAT、POD、APX) compared with WT plants under water stress.(7) Immumology analysis of carbonyls protein indicated that the contents of proteincarbonyls were increased by water stress in both transgenic tobaccos and WT. However, theamount of protein carbonylation products accumulated in WT was greater than that intransgenic tobacco under normal and water stress conditions.(8) Under salt stress, P10::TaEXPB23transgenic lines (transgenic Arabidopsis andtobacco) showed a significantly higher germination rate and a better seedling growth.In conclusion, the present study suggests that the transgenic lines expressing ofTaEXPB23using the root-specific promoter show a normal phenotype under normal growthcondition. Meanwhile, root-specific P10::TaEXPB23expression improved the tolerance oftransgenic tobacco plants under osmotic stress conditions through root biomass enhancementand greater antioxidant competence.