Effects Of Overexpression Of StP5CS Gene On Growth And Nitrogen Fixation In Vegetable Soybean Under Drought Conditions

Vegetable soybeans[Glycine max(L.)Merr.]are harvested during the prime period of soybean growth and eaten as vegetables or snacks.Drought stress is an important factor that limiting soybean growth and nodulation and nitrogen fixation process,which seriously affects soybean biomass and quality.The final product encoded by the StP5CS gene of wild eggplant(Solanum lorvum Swartz)is proline,which plays an important role in mitigating drought damage.This experiment adopts the method of vermiculite cultivation,the two T4 homozygous transgenic lines(HTLs)of vegetable soybean preserved in our laboratory are further self-crossed to obtain T6 HTLs,and T6HTLs containing StP5CS gene are compared with WT vegetable soybean after 3 weeks drought treatment to observe the differences in growth,nodulation and nitrogen fixation indexes.In order to obtain a new drought-resistant vegetable soybean variety with high nitrogen fixation.The main results are as follows:(1)The two StP5CS T6 HTLs vegetable soybean and their wild-type(WT)were used as experimental materials.The growth and physiological aspects were compared between transgenic plants and WT plants after 3 weeks drought treatment.The main results are as follows:After 3 weeks drought treatment,the plant height,stem diameter,root length,shoot weight and seed yield were significantly higher than those of WT plants;transgenic plants have significantly higher osmotic substances proline and soluble sugar than WT plants;antioxidant SOD and POD activities of transgenic plants were significantly higher than those of WT plants;the wilting index of transgenic plants and the content of MDA in leaves were significantly lower than those of WT plants.The above results indicated that the overexpression of StP5CS gene significantly increased the drought tolerance of vegetable soybean under drought conditions,and promoted the growth and development of vegetable soybean plants.(2)The StP5CS T6 homozygous transgenic lines(HTLs)of vegetable soybean were grown using vermiculite pot culture to investigate the effect of StP5CS gene overexpression on photosynthesis in vegetable soybean under drought stress,the results shows:After 3 weeks of drought treatment,the leaf area and relative chlorophyll content of the transgenic plants were significantly higher than those of the WT plants;compared with the WT plants,the net photosynthetic rate(Pn)and Ci of the transgenic vegetable soybean were significantly increased;the relative expression of rubisco and cytochrome c oxidase genes in transgenic plants were significantly higher than that in WT plants.The results indicate that under drought stress,the overexpression of StP5CS gene significantly increased the photosynthesis and antioxidant enzyme activities of vegetable soybean,further indicating that overexpression of StP5CS gene can alleviate the damage of drought sterss on plants,and promote the plant growth and development of vegetable soybean.(3)The StP5CS T6 homozygous transgenic lines(HTLs)of vegetable soybean were grown using vermiculite pot culture to determine whether StP5CS overexpression would enhance nodulation and nitrogen fixation in two T6 HTLs(17W-1,17W-2)under drought conditions.The growth performance,nodule development and seed weight of T6 HTLs were significantly better than those of wild type(WT)plants.The proline levels in various tissues of T6 HTLs were higher than those of WT plants.The concentrations of total ureide,total N,leghemoglobin(Lb)and the activity of glutamine synthetase(GS,EC 6.3.1.2)in the T6 HTLs were significantly increased.Moreover,the relative expression levels of five key nodulation-and SNF-associated genes(i.e.,GmENOD40-1,GmENOD40-2,GmLba,GmGS1βl and GmGS1β2)were significantly higher in T6 HTLs.In conclusion,overexpression of StP5CS enhances nodulation and symbiotic nitrogen fixation in transgenic vegetable soybean under drought stress conditions.