Sorghum HKTGene Na~+/K~+ Transport Key Sites And Drought Resistance Analysis

Abiotic stress such as drought,saline and alkaline is one of the significant factors affecting plant growth and restricting agricultural production in our country for a long time.With the increasing number of population and the continuous decrease of available land area,maximizing the use of marginal land such as drought and saline is particularly urgent.Sorghum（Sorghum bicolor（L.）Moench）which is gramineous C₄ plants with tolerance to drought,salinity and the ability of high biological yield,is an ideal energy plant growing on marginal land.Making full use of its good genetic traits,analyzing the important tolerance-related genes by genetic engineering methods is an effective way for obtaining more plants with drought or salt tolerance.HKT（High affinity potassium transporter）transporters have the capacity to transport Na⁺ and K⁺ under salt stress.In Sorghum,four members of the gene family have identified,such as SbHKT1;4,SbHKT1;5 and SbHKT2;1.SbHKT1;4 has the strongest capacity to transport Na⁺/K⁺.However,the capacity for the key sites of ion transport have not well studied,as well as drought tolerance of SbHKTs.This thesis analyzes the function of SbHKT as follows:Study the SbHKT1;4 key sites which regulate ion transport by heterogeneous expression system yeast and Arabidopsis thaliana.Transient expression the key sites mutation of expected Na⁺ transport Q303,N398 and E495 sites in Nicotiana benthamiana L.demonstrated that they resided on plasma membrane and the nucleus.Heterogeneous expression analysis in Arabidopsis thaliana indicated that SbHKT1;4 mutant genes did not lead to salt sensitive phynotype,which is opposite to wild SbHKTl;4.Functional complementary analysis of the key sites related to K⁺ transport S121 and A124 in yeast mutant strain W△6（Mat a ade2 ura3 trpl trk1D::LEU2 trk2D::HIS3）showed that the yeast strains containing mutant genes had a weaker K⁺transport activity than wild SbHKT1;4.We also compared the drought resistance of different transgenic lines,SbHKT1;4/athkt1-1,SbHKT1;5/athkt1-1 and SbHKT2;1/athktl-1.After water stress,which was simulated by polyethylene glycol（PEG-6000）treatment,we found that transgenic lines were more drought-tolerant than athktl-1 mutant line.This indicated that SbHKTs exert significant function in the presence of drought-stress.In summary,this thesis analyzed five key sites which regulate ion transport ability of SbHKT1;4 in a sense.Meanwhile,we found that SbHKTs not only plays an important role in plant resistance to salt,but also has certain function in terms of drought resistance.These results provide a theoretical basis for the salt-tolerant genes renovation,and give a futher understanding of SbHKTs function.