Characterization And Function Of TaSPX129 On Mediating Tolerance To Pi Deprivation And Other Abiotic Stresses In Wheat

Improving resistance of plants to abiotic stresses is of great significance to plant growth,development and yield formation.The SPX family genes play an important role in maintaining phosphorus homeostasis.In this study,TaSPX129,a member which belongs to SPX gene family was identified in wheat.Molecular characterization,expression patterns and biological functions of TaSPX129 mediating plant responses to low phosphorus and salt stress were studied.The main results are as follows:By querying the protein of SPX domain in the Phytozome website Triticum aestivum v2.2 wheat genome database,a total of 87 SPX family gene-encoding protein sequences were obtained,corresponding to 39 genes,which were divided into four subfamilies according to C-terminal domains.The four subfamilies are SPX,SPX-MFS,SPX-EXS and SPX-RING,each containing 15,11,7 and 6members.The TaSPX129 belongs to the SPX-MFS subfamily and is localized to the tonoplast.The expression patterns of TaSPX129 in response to abiotic stresses were studied.The results showed that under low phosphorus stress of 20?M concentration,the expression of TaSPX129 in wheat root showed an upward trend,and reached the highest level within 1 h.Different from roots,the expression of TaSPX129 in new leaves was gradually decreased in the range of 27 h,while in old leaves,the expression was gradually increased.Under the 75 mM NaCl salt stress,the expression of TaSPX129 in wheat roots and old leaves was similarly to that in roots under low phosphorus treatment.However,the treatment of 9 h in new leaves also increased,and there was little change at other time points.Combined agar,hydroponic and vermiculite culture,the phenotypic characteristics of over expressing TaSPX129 tobacco transgenic lines were studied.The results showed transgenic plants confer improved seedling growth,increased leaf area and root number,along with the increased of chlorophyll content,etc.Further studies were conducted on the expression patterns of important genes respectively involved in low phosphorus and salt stress,and the results showed the phosphorus transporter genes including NtPT4 and NtPT5 were up-regulated in both roots and leaves of transgenic tobacco plants.Under NaCl stress,ABA receptor genes including NtSAPK2-25,NtSAPK7 and NtSPK7 were up-regulated in leaves,and there were several receptor genes up-regulated in roots.In addition,NtPT4 and NtPT5,which were up-regulated after low phosphorus stress,were also up-regulated in roots of transgenic lines treated with NaCl.These results indicated that TaSPX129may enhance the resistance to low phosphorus and salt stress through regulating phosphorus uptake and ABA signaling transduction pathway.Reactive oxygen scavenging parameters including the activities and gene expression patterns of cell protective enzymes in transgenic compared with WT plants were analyzed under low phosphorus and NaCl stress.It was found that activities SOD,POD and CAT were increased in transgenic plants under both low phosphorus and salt stress,while MDA content was decreased.Expression analysis revealed that expression of antioxidant enzyme encoding gene POD1;2,POD4,CAT1;1,CAT1;2 and CAT1;3 were up-regulated in transgenic line root under above treatments.The detection of in situ accumulation for H₂O₂ and O₂^-·were carried out using NBT and DAB staining methods,and the leaves of the transgenic tobacco were found both lighter than those of wild type,indicating the relative lower content of H₂O₂ and O₂^-·.So these results suggest that TaSPX129 could improve the scavenging ability of H₂O₂ and O₂^-·by regulating the activity and expression level of protective enzyme,which contributes to the plant tolerance to abiotic stresses.Consider as the growth advantages of over expressing TaSPX129 tobacco transgenic lines,the ability of transgenic plants to resist salt stress was further identified by investigating biochemical parameters such as proline,soluble sugar and protein content,relative ion leakage,along with stomatal characteristics.The results showed content of Pro and soluble sugar increased,while the relative ion leakage decreased compared with the wild type.In addition,the stomatal closure was faster in transgenic plants.So these results showed that the transgenic plants have stronger osmotic regulation ability under salt stress.Combined with faster stomatal closure and enhanced expression of mentioned ABA receptor gene,which indicated again that ABA signaling pathway may participate important role in responding to salt stress.To sum up,TaSPX129 plays an important role in enhancing the ability to resist low phosphorus and salt stress in plants,and the regulatory network along with the molecular mechanism were still need to be further studied.