The Mechanism Of Arbuscular Mycorrhizal Symbiosis Improving Salt Tolerance Of Sour Jujube Seedlings

Jujube(Ziziphus jujuba Mill.)is an important economic forest tree species in China and an important industrial tree species for rural revitalization in northwest China.Salinization of soil is the main adverse factor affecting the growth of jujube trees in northwest China.Sour jujube(Ziziphus acidojujuba Mill.)as the rootstock of jujube and can symbiosis with arbuscular mycorrhizal fungi to improve the growth condition of jujube tree.In this study,sour jujube seedlings and Rhizophagus irregularis(RI)were used as materials and treated with different concentrations of Na Cl to study the growth status,photosynthesis,and response to ion homeostasis of jujube seedlings under mycorrhizal symbiosis and Na Cl stress.In addition,comparative transcriptome analysis was carried out to reveal the physiological and molecular regulation mechanism of AMF inoculation to improve the salt tolerance of sour jujube under salt stress.The main results were as follows:(1)Salt stress significantly inhibited the growth of sour jujube seedlings.With the increase of Na Cl concentration,the biomass of sour jujube seedlings was significantly reduced and the growth of new leaves growth was inhibited.At 13 d of treatment,dead plants appeared in the 150 and 200m M Na Cl treatment group,and the jujube seedlings in the 100m M Na Cl treatment group could maintain growth.(2)Mycorrhizal symbiosis improve the photosynthesis and antioxidant enzyme activity of sour jujube seedlings under salt stress.Inoculation of AMF significantly improve Pn,Fv/Fm,Fv/Fm in sour jujube seedlings and reduces the NPQ.Mycorrhizal symbiosis increased the activity of SOD,CAT and POD,decreased the content of MDA,in roots,the inoculation of AMF increased the activity of POD and CAT.(3)Mycorrhizal symbiosis improved the nutrient level and element state of sour jujube seedlings by regulating element absorption and transport under salt stress.inoculation with AMF was contained higher P,K,Na and Ca content in the tissues of sour jujube seedlings than without inoculation seedlings,and the K/Na ratio was significantly increased.K/Na ratio in AM100 leaves was significantly higher than that in NM100.The Na~+flow rate of root tip measured by non-damage detection technology,results showed that the Na~+efficient exudation region was in the range of 200-1100?m from root tip,and the difference was significant between mycorrhizal and non-mycorrhizal roots in the range of 200-800?m.Inoculation of AMF changed the direction of H~+flow rate of sour jujube seedlings and reduced the K~+flow rate in root tip after salt stress,indicating that AMF responded to salt stress through H~+efflux and reduced K~+efflux.(4)The comparative transcriptome analysis showed,under salt stress,AMF inoculated and uninoculated treatments(GT1-T1)regulated 814 and 1028 differentially expressed genes in leaves and roots,respectively.These DEGs were mainly enriched in carbohydrate metabolism,hydrolase activity,ion transporter activity,lipid metabolism process,transcription regulation activity and oxidoreductase activity in GO terms.Inoculation of AMF could respond to salt stress by affecting the activation of genes related to energy metabolism ion absorption,transport and transcription regulation activity of sour jujube seedlings.The expression of the three main family genes of AP2/ERF,WRKY and MYB in mycorrhizal symbiosis is significantly regulated;the biosynthesis and signal transduction genes related to IAA and JA in leaves were significantly up-regulated compared with uninoculated sour jujube seedling.The up-regulation of the expression of biosynthetic genes also showed that mycorrhizal symbiosis increased the expression of related hormone biosynthesis genes,which made the hormones in plant roots,and enhanced sour jujube seedlings salt resistance ability.(5)Under salt stress,mycorrhizal symbiosis regulated the expression of genes encoding ion transport and channel proteins.After salt stress,mycorrhizal symbiosis reduced K~+effluents by regulating the expression of Zj NHX?Zj ATPase?Zj ATPase and Zj SKOR.After screening the P transporter genes,7 members of the PHT1 gene family were identified;in inoculated sour jujube seedlings,Zj PHT1.5,Zj PHT 1.6,and Zj PHT 1.7 were selectively induced to up-regulate expression under different Na Cl treatment times,and regulated P transport,while Zj PHT1.3 and Zj PHT1.11 showed a specific expression pattern related to mycorrhizal symbiosis.In this study,under salt stress,the Na Cl concentration threshold for jujube seedlings to maintain growth is 100 m M;at the physiological level,mycorrhizal symbiosis is mainly achieved by increasing the photosynthesis,antioxidant enzyme activity,endogenous hormone content of jujube and increasing leaf,the four main ways to increase the nutrient level of plants and maintain ion homeostasis,make the jujube obtain systemic resistance.At the transcriptional level,mycorrhizal symbiosis is through the regulation of carbohydrate metabolism and signal transfer.The expression of genes such as conductance,ion transport across membranes and transcriptional regulatory activity responds to salt stress.