Combined Transcriptome And Proteome Analysis Reveals The Salt Tolerance Mechanism Of Hybrid Mulberry

Mulberry（Morus spp.）is an important economic tree species originating in China.It has strong tolerance to environmental stresses such as salinity,drought and heavy metal stress.It has strong vitality and is widely distributed around the world.As one of the tree species of ecological shelterbelt system in China,mulberry can protect soil structure,reduce surface runoff,and play the role of soil consolidation and sand control.Due to the rapid growth of mulberry trees and their large biomass,they have significant restoration effects on the Gobi desertification areas,barren deserts with more rocks,and soils containing heavy metals.The utilization of mulberry for feeding,medicinal and ecological management has attracted the attention of researchers in recent years,and"making mulberry as an industry"has become a consensus.The molecular mechanism of mulberry response to salt stress is still unclear,and the phenotypic,physiological,and combined proteome-transcriptome analysis of salt-tolerant and salt-sensitive mulberry have not been reported.In order to clarify the molecular mechanism of mulberry salt tolerance,this study screened mulberry salt-tolerant and salt-sensitive varieties from hybrid mulberry,and analyzed the phenotype and physiological characteristics of salt-sensitive and salt-tolerant varieties,focusing on the changes in the proteomic and transcriptomic profile of mulberry in response to salt stress.Combined with GO,KEGG and other databases to screen differentially expressed proteins and genes,and identify salt resistance-related proteins.This study clarified the molecular mechanism of mulberry salt tolerance,laid a theoretical foundation for further improving the physiological and molecular mechanism of mulberry salt stress regulation,and had application value for saline alkali land management and screening salt tolerant germplasm.The main results were as follows:1.Screen out the salt-sensitive and salt-tolerant mulberry varietiesIn this study,12 hybrid mulberries were subjected to high salt stress and the salt-sensitive variety"Guisangyou 12"and the salt-tolerant variety"Jisang 3"were identified.2.Analysis of salt tolerance of mulberry at physiological levelBefore salt stress treatment,the net photosynthetic rate and antioxidant capacity of"Jisang 3"were significantly higher than those of"Guisangyou 12",but the intercellular carbon dioxide concentration has no significant difference between the two.After salt stress treatment,the seedlings of the salt-tolerant variety"Jisang 3"did not show obvious stress phenotype,while the seedlings of the salt-sensitive variety"Guisangyou 12"shrank and wrinkled,and the leaves dried up and fell off.After salt stress,the photosynthetic rate and photosynthetic efficiency of the two mulberry cultivars decreased significantly,the sodium ion content in the tissue increased significantly,and the potassium ion and calcium ion content was tend to decrease,but the antioxidant capacity of the two cultivars has no significant difference.Salt stress led to a significant increase in the intercellular CO₂concentration of"Jisang 3",indicating that its respiration was enhanced.Under salt stress,the relative water content of leaves of the salt-tolerant variety"Jisang 3"did not change much,while the sensitive variety"Guisangyou 12"suffered severe water loss.The above results showed that"Jisang 3"seedlings were more adaptable to high salinity environment.3.Transcriptomic analysis of the molecular mechanism of mulberry salt toleranceTranscriptomic analysis found that,after salt stress treatment,there were 683 and 1060differentially expressed genes in"Jisang 3"and"Guisangyou 12",respectively.GO analysis found that in the two varieties of mulberry,redox reactions were significantly enriched,the response to abiotic stress was significantly up-regulated,while cell wall and other cell structure-related genes were significantly down-regulated;KEGG analysis showed that phenylpropanoid metabolic pathway and MAPK signal Pathway-related genes were significantly induced by salt treatment,and in the salt-tolerant cultivar"Jisang 3",more genes in the two metabolic pathways were induced at the transcriptional level,indicating that phenylpropanoid metabolism is closely related to the response process of mulberry to salt-tolerant stress.related.4.Proteomic analysis of molecular mechanism of salt tolerance in mulberryA total of 7044 proteins were identified by proteomics,of which 6877 could be quantitatively analyzed.Under salt stress,there were 255 different-regulated proteins（71up-regulated and 117 down-regulated）in"Guisangyou 12",and 600 up-regulated proteins and 619 down-regulated proteins in salt-tolerant mulberry"Jisang 3".Under salt stress,the differentially expressed proteins of"Guisangyou 12"were enriched in the biosynthesis of glucosinolates,amino acids and degradation pathways,such as alanine metabolism,valine,cleavage degradation,isoleucine degradation,leucine and fatty acid degradation,and down-regulated proteins were mainly enriched in phenylpropanoid biosynthesis and steroid biosynthesis pathways.In"Jisang 3",the up-regulated proteins were enriched in phagosome,cytosine,endocytosis and phenylpropanoid biosynthesis pathways,while the down-regulated proteins were enriched in carbon metabolism,glycolysis,gluconeogenesis,proline and arginine metabolism pathways.In conclusion,a large number of phenylpropanoid biosynthesis-related proteins are up-regulated by high salinity,while proteins involved in carbon metabolism were down-regulated.This provides an important clue for revealing the mechanism of salt tolerance of mulberry.5.Transcriptomic and proteomic analysis reveals salt tolerance mechanism of mulberryTranscriptome and proteomic analysis showed that the gene transcription level of"Jishang 3"was consistent with that of protein abundance,while that of"Guisangyou 12"was inconsistent with that of protein abundance.Combined transcriptomic and proteomic analysis showed that,the levels of salt-induced genes and proteins involved in plant hormone signal transduction and phenylpropanoid biosynthesis were positively correlated with seedling salt tolerance.Both coumarin and flavonoids were induced in phenylpropane biosynthesis of mulberry under salt stress,suggesting that phenylpropane biosynthesis was involved in salt response.