Physiological Response And Transcriptomic Analysis Of Desert Plant Zygophyllum Xanthoxylum Under Heat Treatment

High temperature is one of the main abiotic stress factors that limit agricultural production.Zygophyllum xanthoxylum,a widely distributed plant in the arid desert region of northwest China,is a typical succulent xerophyte with excellent heat resistance.Z.xanthoxylum contains abundant stress-resistant genetic resources as well as potential utilization value.However,physiological mechanism and molecular basis of heat tolerance is still unclear in Z.xanthoxylum.In this study,Z.xanthoxylum seedlings were treated with high temperature,in order to reveal the physiological mechanism of its resistance to high temperature preliminarily.By using RNA-seq sequencing,we obtained the transcriptome data of Z.xanthoxylum under heat treatment and analyzed the differentially expressed genes(DEGs)related to transcription factor,heat shock protein,antioxidant system and photosynthesis in Z.xanthoxylum.The major results are as follows:1.After 10 days(6 h·d^-1)of treatment at 40? and 45?,compared with the control group(25?,16 h·d^-1),the dry weight and fresh weight of the Z.xanthoxylum under 40? treatment increased by 24.3%and 33.4%,the relative growth rate of whole plant increased by 57.2%,and the net photosynthetic rate of leaves increased by 29.3%,while the growth and net photosynthetic rate of Z.xanthoxylum were severely inhibited under the 45? treatment,It shows that 40? treatment significantly promoted the growth of Z.xanthoxylum,while 45? treatment had an inhibitory effect on its growth;Compared with the control group,high temperature had no significant effect on the plasma membrane permeability of the leaves,and the osmotic potential decreased with the increase of the temperature.In addition,the content of proline and soluble sugar in the leaves of Z.xanthoxylum increased by 85.1%and 33.3%at 45? treatment compared with the control,and content of K⁺in the stem of Z.xanthoxylum increased by 66.7%and 55.6%.2.A transcriptome sequencing on Z.xanthoxylum seedlings which treated with40? and 45? for 0.5 or 6 hours respectively,and total 166892 unigenes with an average length of 1534 bp were obtained.Then,139130 unigenes(83.4%of the all-unigenes)were annotated to the known genes in the public databases,including Nr,Nt,Swissprot,KEGG,COG,Interpro and GO.3.Short-term heat treatment(40? and 45? with 0.5 h)significantly induced the expression of genes encoding HSF,bHLH,AP2/ERF,bZIP,MYB and WRKY transcription factor families associated with stress response in the leaves and roots of Z.xanthoxylum.Among them,the number of up-regulated genes in the leaves of Z.xanthoxylum after treatment at 40? and 45? for 0.5 h was significantly higher than that of 6 h.In addition,the number of WRKY family genes in leaves and HSF family genes at 45? treatment increased significantly higher than 40? treatment,The results showed that compared with 40? treatment,Z.xanthoxylum needed to up-regulate the expression of more WRKY and HSF family genes in response to 45? heat stress.4.When treated at 40? and 45? for 0.5 h,the expression abundance of heat shock protein-coding genes of HSP70,HSP90,small HSP(sHSP),HSP70-HSP90 and ClpB genes significantly up-regulated in the root and leaves of Z.xanthoxylum,indicating that heat shock protein genes played a key role response to high temperature in Z.xanthoxylum.In addition,the up-regulated number of HSP70 genes in leaves,HSP90 and sHSP genes in roots at 45? were significantly higher than that of 40? treatment for 0.5 h,indicating that these three heat shock proteins in Z.xanthoxylum may play a crucial role in response to 45? heat stress.5.Under the treatment of 40? and 45?,the expression abundance of reactive oxygen scavenging enzyme genes in the root and leaves of Z.xanthoxylum was significantly up-regulated,which was conducive to relieve the ROS damage to the cell membrane system.Among them,the expressions of SOD,GST,Trx,APX and GLR encoding genes we re significantly induced by high temperature treatment for0.5h.After 40? and 45? treatment for 6 h,SOD,Trx,APX,GLR and GST coding genes still highly expressed,and the total number of genes related to ROS scavenging at 45? treatment were higher than that of 40? treatment,which helped to alleviate the damage of ROS to plants.6.After treatment at 40?,the net photosynthetic rate and stomatal conductance of leaves were significantly higher than the control.Moreover,the expression abundance of genes related to photosystem II and carbon fixation enzymes was up-regulated in the leaves of Z.xanthoxylum;The results showed that the 40? treatment increased the stomatal conductance of leaves to increase the supply of CO₂,and activate the expression of a large number of photosynthesis-related genes,which increased the net photosynthetic rate of leaves together.In addition,the increase of stomatal conductance reduced leaf temperature.Although stomatal conductance was higher than that of control,net photosynthetic rate decreased significantly after treatment at45?,and the number of down-regulated expression genes belong to photosynthetic electron transporter subunits and photosynthetic carbon fixation in the leaves of Z.xanthoxylum were more than that of up-regulated,the results showed that the non-stomatal factors were the main reason for limiting photosynthesis of Z.xanthoxylum under 45? heat stress.