| Maize(Zea mays L.)is a multi-purpose crop that combines grain,feed,biofuels and other functions.Its level of production is related to the country’s food security and economic development.Salt stress is one of the most common adverse stresses in agricultural production,and has a serious of impacts on the growth and yield of corn.Land salinization has become an important factor restricting corn production in China.Therefore,the mechanism of maize in response to salt stress and elucidate its salt-tolerance mechanism,excavate the genes associated with salt tolerance and breed new salt-tolerant strains by molecular methods,which has important theoretical significance for improving the salt tolerance of maize,and certain practical application value for corn production.Exogenous betaine,as an effective osmoregulatory substance,can reduce the adverse effects of salt stress on maize growth and improve the tolerance of maize to salt stress.In order to reaserch the salt-tolerance mechanism of maize and the effect of exogenous betaine on maize under salt stress,we studied the significant differences under the salt stress between two maize inbred lines(salt-sensitive inbred lines P138 and salt-tolerant inbred lines8723).For the test materials,their differences in morphology,cell structure,physiology and biochemistry were analysed under salt stress and exogenous betaine treatment;the metabolic regulatory networks related to salt tolerance were studied from the perspective of transcriptomics and proteomics.The main findings were as follows:1.The ion content and the cell structure of the two inbred lines under NaCl stress treatment and exogenous betaine can relieve salt stress by comparing the morphological,physiological and biochemical indexes.The results showed that NaCl stress significantly inhibited the growth and development of the salt-sensitive inbred line P138,broke the ion balance in the body,resulting in the cell morphology of its root system.There were a large number of dead cells in the parenchyma cells,and the diameter of the catheter became smaller.The salt-tolerant inbred line 8723 resisted salt damage by maintaining high SOD,POD and CAT activity,relative water content and maintaining a higher K~+/Na~+ratio during NaCl stress.NaCl stress,the suitable concentration of exogenous betaine could effectively alleviate the damage caused by NaCl stress to the two inbred lines.Through the comparison of the indexes of two inbred lines,it was found that exogenous betaine had a greater relief to salt-sensitive inbred line P138,which indicated that it had better inhibition effect on salt-tolerance materials.2.RNA-Seq technology was used to compare the differential expression genes of root system in the two inbred lines under NaCl stress treatment and exogenous betaine relieving NaCl stress.The results showed that more differential genes were up-regulated in salt-tolerant inbred line 8723 under the NaCl stress,which were the difference between the salt-sensitive inbred line P138 and the salt-tolerant inbred line8723.The addition of exogenous betaine could change the expression pattern of more genes in salt-sensitive inbred line P138 to response the salt stress.43,85 and 33distinct up-regulated genes were identified in different comparison groups.The GO analysis showed that these significant common expression genes mainly participate in the chitin catabolic process,cell wall macromolecular catabolism process,polysaccharide metabolic process,oxygenation reduction process,carbohydrate transmembrane transport,oxidative stress,cell oxidative detoxification,hydrogen peroxide decomposition,ion transport and salt stress.3.Preliminarily identified 12 genes,including the KUP family,the Na~+/H~+ion exchange(9 member of the solute family),the nicotinamide synthase,the cytochrome P450 family,the UDP-glucose,the oxide enzyme and the L-ascorbic acid oxidase,as candidate genes for the salt tolerance of maize.4.The iTRAQ technique was used to study the proteomics of the roots of two inbred lines under the NaCl stress.The results showed that there were 473 differential proteins,212 up-regulated and 261 down-regulated proteins in salt-sensitive inbred lines P138 under the NaCl stress.And 626 differential proteins,378 up-regulated and248 down-regulation in salt-tolerant inbred lines 8723.Under salt stress,salt-tolerance inbred line 8723 could resist salt stress by changing more protein expression patterns.Venn analysis showed that 17 of the two inbred lines were up-regulated,and 8 of the differential proteins were up-regulated in the salt-tolerant inbred line 8723 and down-regulated in the salt-sensitive inbred line P138.They were mainly involved in biological processes such as energy metabolism,stress defense and signal transduction.Effective regulation of protein expression related to energy and stress defense signaling played a key role in improving salt tolerance of maize.5.Pathway enrichment analysis of differential proteins showed that the two inbred lines had significant accumulation of differential proteins on the MAPK signaling pathway.In response to salt stress,the 2 differential proteins were down-regulated for the salt-sensitive inbred line P138 and a differential protein was significantly up-regulated for the salt-tolerant inbred line 8723 in MAPK signaling pathway,which was the important difference between the salt-sensitive inbred line P138 and the salt-tolerant inbred line 8723.An important manifestation of the metabolic pathway affecting photosynthesis,the significant down-regulation of differential proteins directly affected the development of the lateral root of the salt-sensitive inbred line P138 and the response to the adversity.In summary,these findings illuminate the processes of different maize inbred lines in response to salt stress and exogenous betaine in morphology,physiology,biochemistry,cell structure,transcriptomics,and proteomics.Some genes related to salt tolerance provide theoretical basis and technical support for the further study of salt tolerance mechanism and salt tolerant breeding in maize. |
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