Analysis Of The Regulatory Mechanism Of Poplar MPK7 Gene In Response To Salt Stress Based On The Combination Of Multi-omics

Soil salinization severely limits the productivity of agroforestry,and salt stress can cause continuous and complex effects on plants.Poplar,as one of the most widely distributed tree species in the northern hemisphere,has important economic,ecological and ornamental values,and is also a model plant for molecular biology research in forest trees.The mitogen-activated protein kinase(MAPK)cascade pathway is a conserved signal transduction pathway in eukaryotes,and it is responsible for receiving and transmitting stress signals to downstream target proteins,which in turn regulate the expression of stress-responsive genes.In this study,the Pe MPK7-overexpressing poplar transgenic plants(OE 1-6)and wild-type poplar plants(WT)were used as materials.The hydroponic plantlets were treated with 150 m M Na Cl stress,and the regulatory network and molecular mechanism of poplar Pe MPK7 gene in response to salt stress were explored using a combination of transcriptomic,metabolomic,phytohormone assay techniques and bioinformatics approaches.The main results are as follows:1.Under salt stress,the leaves and petioles of OE 1-6 and WT poplar plantlets in the middle and upper parts of the plantlets rapidly wilted due to osmotic stress and then gradually recovered.OE 1-6 was less damaged by salt stress and recovered better than WT,and the cell membranes were also less damaged than WT.2.Transcriptome sequencing results showed that OE 1-6 and WT had a total of 18768 differentially expressed genes(DEGs)under salt stress,including 1583 annotated differentially expressed transcription factors(TFs);OE 1-6 had a total of 1737 DEGs compared to WT,including 189 annotated TFs and a large number of DEGs related to signaling,plant hormone synthesis and transduction,osmoregulation,ion regionalization and antioxidant.3.Metabolite measurement results showed that there were 156 differentially accumulated metabolites(DAMs)in OE 1-6 and 77 DAMs in WT under salt stress,and 49 of them were overlapping DAMs.Among the DAMs,the content of 22 DAMs was up-regulated,most of which belonged to amino acids and their derivatives;and the content of 26 DAMs was downregulated,most of which were organic acids and lipids.Compared with WT,there were 71 DAMs in OE 1-6 under salt stress,among which the content of DAMs such as galactose,Dmannitol,L-proline,L-valine,L-histidine and L-phenylalanine was up-regulated.4.Phytohormones content analysis showed that the content of abscisic acid(ABA)significantly jumped in poplar under salt stress,and the content of ABA in OE 1-6 was higher than that in WT.The content of auxin(IAA)in OE 1-6 was lower than that in WT under normal conditions,but it was higher in OE 1-6 than that in WT under salt stress.The content of two cytokinins IPA and T-Zeatin in OE 1-6 was higher than that in WT under normal conditions.The content of IPA and T-Zeatin increased in both OE 1-6 and WT under salt stress,with higher content in OE 1-6 than in WT.The content of gibberellin GA1 in poplar reduced under salt stress,but the content of GA1 in OE 1-6 was higher than in WT under both normal conditions and salt stress;in contrast,the content of gibberellin GA3 in poplar increased under salt stress,and its content in OE1-6 was not significantly different with WT under normal conditions,while its content was significantly lower in OE1-6 than in WT under salt stress.5.KEGG co-enrichment analysis of transcriptome and metabolome revealed that a large number of amino acid synthesis and metabolic pathways were enriched in poplar after salt stress.Compared to WT,multiple amino acid synthesis and metabolic pathways were also enriched in OE 1-6 under salt stress.This result indicated that amino acid metabolic pathways play a key role in the Pe MPK7-mediated regulatory network of salt stress.To sum up,Pe MPK7 overexpression caused differential gene expression,differential metabolites accumulation,and phytohormone content changes in poplar,resulting in a complex and precise regulatory network responding to salt stress in poplar.This study will provide important information for the breeding research of salt tolerance in poplar.