| The apple(Malus pumila Mill)is one of the most important fruits in the world and an important fruit tree species in China.Apples are widely cultivated in China,but soil salinization seriously threatens their growth and yield quality.The research group used Na Cl stress to treat the hybrid offspring of Xinjiang wild apple(♂)× anvil(♀)in the early stage,and obtained 18 descendants of extreme salt tolerance and extreme salt intolerance after phenotypic screening,and constructed mixed pools for the descendants of extreme salt tolerance and extreme salt intolerance phenotypes and performed transcriptome sequencing and BSR analysis,compared transcriptome analysis to obtain candidate genes that were differentially expressed in extreme salt tolerance and extreme salt intolerance,and verified the expression by functional screening of differential genes,sequence difference analysis between parents and q RT-PCR.It was found that the sequences of MdXTH1 and MdXTH23 genes were different between parents and their expression patterns were consistent with the salt stress phenotype,which may be the key functional genes of hybrid offspring in response to salt stress,and the salt tolerance function of MdXTH15 and MdXTH23 genes was verified in this study.The main findings are as follows:1.The total length of the MdXTH15 gene open reading frame is 828 bp,encoding 276 amino acids;The MdXTH23 gene open reading frame has a total length of 870 bp and encodes 290 amino acids.The amino acids encoded by MdXTH15 and MdXTH23 genes were highly conserved and had two highly conserved domains,and the physicochemical properties of the amino acids encoded by MdXTH15 and MdXTH23 genes were analyzed,and it was found that MdXTH15 and MdXTH23 amino acids were hydrophilic amino acids.A total of 38 XTH family genes were identified in the apple genome,and the MdXTH15 and MdXTH23 genes were located in the same evolutionary branch,and the family genes on different evolutionary branches had the same motif distribution pattern.2.The RNA-seq results were verified by q RT-PCR,and there were significant differences in the expression of MdXTH15 and MdXTH23 genes in the descendants of extreme salt tolerance and extreme salt intolerance.The CDS sequence of the MdXTH15 gene has a base difference in the two parents,resulting in a change in its protein sequence,and the presumptive function has also changed,and it is necessary to conduct subsequent functional verification of the MdXTH15 gene.3.Under Na Cl stress,35S::MdXTH15 Arabidopsis thaliana had longer taproot and higher plant height.The results showed that the callus of 35S::MdXTH15 apple grew well under Na Cl stress,while the callus of WT apple was severely browned,and the results showed that the callus of35S::MdXTH15 apple could enhance the tolerance of apple callus to salt stress under salt stress conditions,so that apple callus could maintain normal growth under salt stress conditions.By measuring the physical and chemical indexes of POD,SOD and malondialdehyde under Na Cl stress,it was found that the clearance ability of 35S::MdXTH15 apple callus and Arabidopsis thaliana ROS was significantly improved,and the degree of cell toxicity was lower.35S::MdXTH15 Arabidopsis thaliana chlorophyll a content was significantly increased.The expression of key genes of SOS pathway(an important defense pathway for plants tolerating Na+stression)and antioxidant enzyme-related genes in the callus of 35S::MdXTH15 apple callus was increased,indicating that MdXTH15 was induced by salt stress and was a key gene in response to salt stress.4.In the Na Cl stress environment,there was no significant difference between the root length and plant height of 35S::MdXTH23 Arabidopsis thaliana and WT Arabidopsis thaliana in the salt stress environment,and the POD,SOD enzyme activity and malondialdehyde content were measured at the same time,and it was found that there were no significant differences between the POD,SOD activity and malondialdehyde content of two lines in 35S::MdXTH23 Arabidopsis thaliana and WT Arabidopsis,and the activity of POD and SOD of the other line was significantly increased,and the content of malondialdehyde was significantly reduced.It shows that the tolerance of 35S::MdXTH23 to Na Cl stressed environment needs further study. |
