Adaptability Comparison Between Cultivated Soybean And Wild Soybean Under Salt And Low Nitrogen Stresses

Soil salinization is one of the most important abiotic stresses affecting agricultural production in the world.In order to pursue high yield of crops,excessive application of nitrogen fertilizer often occurs in production,which not only increases the agricultural cost,but also pollutes the environment.Cultivated soybean is the main oil crop and food crop in the world.Cultivated soybean is a typical sweet soil plant,which is easy to suffer from salt stress,and needs a lot of nitrogen fertilizer in the growth process.Therefore,it is an effective strategy to cultivate soybean with strong salt tolerance and high efficiency to obtain and utilize nitrogen under low nitrogen level.Wild soybean,which has been living in the natural environment for a long time,is a near source wild species of cultivated soybean.It has strong tolerance to saline alkali stress and low nitrogen stress.It is a high-quality wild resource to improve the stress resistance of cultivated soybean.It is one of the effective measures to deal with soil salinization and excessive application of nitrogen fertilizer to cultivate soybean varieties with strong stress resistance by using high-quality wild soybean germplasm resources.In this study,we simulated two types of salt and low nitrogen conditions on cultivated soybean and wild soybean seedlings under neutral salt,alkaline salt and low nitrogen stress treatment.The physiological,metabolic and transcriptome changes of cultivated soybean and wild soybean seedlings under three types of stress were analyzed,and the physiological,metabonomics and transcriptome responses of cultivated soybean and wild soybean seedlings to three types of stress were compared.The main conclusions were as follows:?1?Under the two types of salt stress,wild soybean seedlings showed stronger salt tolerance than cultivated soybean.?2?Under two types of salt stress,wild soybean could maintain stable photosynthetic function.At the same time,wild soybean could maintain a low Na⁺/K⁺value,accumulate beneficial ions such as Fe²⁺and Ca²⁺and stable mineral nutrient balance to reduce the damage caused by salt stress.However,photosynthesis of cultivated soybean was significantly inhibited and ion balance was destroyed under two types of salt stress.?3?The wild soybean seedling roots could enhance the metabolism of amino acids,fatty acids,sugars,sugar alcohols and organic acids,accumulate a large amount of osmotic adjustment metabolites,at the same time,it could enhance the metabolism of phenolic metabolism and improve the neutral salt tolerance.The wild soybean seedling roots enhanced its amino acid and fatty acid metabolism,especially unsaturated fatty acid metabolism and tricarboxylic acid cycle,and improved the metabolism of secondary metabolite flavonoids to resist alkaline salt stress.Under neutral salt stress,the metabolism of amino acids,fatty acids,organic acids,sugars,sugar alcohols and tricarboxylic acid cycle in cultivated soybean seedling roots were inhibited.Under alkaline salt stress,the metabolism of fatty acids,organic acids,sugars and alcohols,and the cycle and secondary metabolism of tricarboxylic acid were inhibited in cultivated soybean,although the metabolism of amino acids was enhanced.Transcriptome analysis showed that there were 139 and 587 differentially expressed genes under neutral salt stress,and 1627 and 5482 differentially expressed genes under alkaline salt stress in wild soybean and cultivated soybean seedling roots respectively.The regulation of Trihelix,WRKY and HB-HD-ZIP family transcription factors under neutral salt stress,and MYB,NAC,TIFY and WRKY family transcription factors played very important positive regulatory roles when wild soybeans resist salt stress.The up regulation of homologous domain leucine zipper protein?HD-Zip?gene under neutral salt stress,and the up regulation of annexin,phosphoenolpyruvate carboxylase,H⁺-ATPase,?-glucosidase,chitinase,glutathione-S-transferase and glutamic acid dehydrogenase play important roles in wild soybean resisting salt stress.Association analysis of metabonomics and transcriptomics showed that the key to resist neutral salt stress was to enhance cyanoamino acid metabolism and flavonoid biosynthesis,the key to resist alkaline salt stress was to enhance tyrosine metabolism,cysteine and methionine metabolism in wild soybean resisting.?4?Wild soybean had stronger tolerance to low nitrogen than cultivated soybean.Wild soybean could resist low nitrogen stress by promoting root growth,maintaining a high ratio of root to shoot,increasing the contact area between root and nutrients,and absorbing more nitrogen to resist low nitrogen stress.?5?Under low nitrogen stress,photosynthesis damage of wild soybean was significantly less than that of cultivated soybean.Wild soybean could maintain stable photosynthetic pigment content and accumulate carotenoids,an important antioxidant substance,to resist low nitrogen stress.Under low nitrogen stress,wild soybean could maintain relatively stable ion content,especially NO₃^-.The accumulation of Fe²⁺and Mn²⁺in wild soybean seedling leaves and roots,Zn²⁺,B³⁺and Mg²⁺in leaves could effectively protect photosynthesis and improve the wild soybean seedling ability of tolerance to low nitrogen stress.However,low nitrogen stress significantly destroyed the absorption of essential mineral elements in cultivated soybean,resulting in a serious imbalance of mineral nutrients.?6?The metabolism of glutamate,aspartic,alanine and serine amino acids in wild soybean seedling leaves and roots were enhanced to resist low nitrogen stress.In addition,the tricarboxylic acid cycle maintained stable in wild soybean seedling leaves and enhanced in wild soybean seedling roots,which provided important metabolic intermediates for plants while ensuring energy supply.The metabolism of sugar,sugar alcohol,organic acid and fatty acid,and flavonoid metabolism in wild soybean seedling leaves and roots were enhanced,which contributed to the improvement of low nitrogen tolerance.Under low nitrogen stress,the whole metabolism level of cultivated soybean seedlings became disordered.Transcriptome analysis showed that there were 182 and 733 differentially expressed genes in wild soybean and cultivated soybean seedling leaves,and 807 and 621 differentially expressed genes in roots under low nitrogen stress respectively.Wild soybean could resist low nitrogen stress by regulating the expression of NRT1?NRT2 and AMT protein family related genes.AP2/ERF-ERF,C2H2,C3H,GRAS,MYB,NAC,TIFY and WRKY transcription factors in leaves,and C2H2,GRAS,MYB,NAC,TIFY and WRKY transcription factors played regulatory roles in the process of wild soybean resisting low nitrogen stress.Combined analysis of metabonomics and transcriptomics showed that the key to resist low nitrogen stress was to enhance the metabolism of cysteine methionine and glutathione in wild soybean seedling leaves,and to enhance the metabolism of cysteine methionine,cyanoamino acid,N-glycan biosynthesis,amino sugar and nucleotide sugar metabolism and glycolysis in wild soybean seedling roots.Combined analysis of metabonomics and transcriptomics showed that phenylalanine metabolism,starch and sucrose metabolism,pentose and glucuronide conversion,galactose metabolism and flavonoid biosynthesis were the key metabolic pathways to resist the three types of stress.In addition,four key genes were found to resist three types of stress in wild soybean.?7?Metabonomics and transcriptomics analysis showed that alkaline salt stress was the most harmful to cultivated soybean.The damage mechanism of neutral salt stress and alkaline salt stress on cultivated soybean seedling root was different.Neutral salt stress was mainly Na⁺and Cl^-combined stress,alkaline salt stress was mainly Na⁺stress and high p H stress.Metabonomics analysis showed that sugar and sugar alcohol metabolism in the roots of cultivated soybean seedlings was the most sensitive and were inhibited under three types of stress.Transcriptomics and metabonomics analysis showed that aspartate and glutamate metabolism,phenylalanine metabolism and glycolysis were the most seriously damaged under three types of salt stress.The results showed that aspartic acid and glutamic acid metabolism,phenylalanine metabolism and glycolysis were the most sensitive to adverse environment after long-term artificial breeding.This study provides new ideas and methods for the development and utilization of wild soybean and the cultivation of salt and alkali tolerance and low nitrogen tolerance of cultivated soybean.It lays an important theoretical foundation for the improvement of saline alkali land,the protection of ecological environment and the sustainable development of agriculture.It provides a scientific basis for improving the stress resistance of other crops and the protection and utilization of high-quality wild resources.